\^
ESRO SP-IOS November 1974 r
H II REGIONS AND ^ THE GALACTIC CENTRE
Proceedings of X" EIGHTH ESLAB SYMPOSIUM ^ 4-7 JUNE 1974 "—f Frascati, Italy f ' -•-•• '" ^ft Edited by A.F.M.Moorwood +' •>£•\ -»-,. I
ORGANISATbN EUROPEENNE DE RECHERCHES SPATIALES EUROPEAN SPACE RESEARCH ORGANISATION OipnnjlU.il lunrprrniii-dr Hrthtrihr- SJMI RLCIOMSIIU iTUSim (.4L\rn
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Iftudr dr%ir| l'uh|rl ilr Jihrci tliwinsiuii. j Ii I . a ta jirrwnlaliuii pi I I'mii-tpt, il »u pai dn Irkv up.-. rmbli<| H II REGIONS AND THE GALACTIC CENTRE Pr(HccJiiiv.s ni EIGHTH ESLAB SYMPOSIUM 4-7 JUNE 1974 Fr usait i. Italy Filitctl by AI.M. Mtmrwtmd ORGANISATION EUROPEENNE DE RECHERCHES SPATIALES EUROPEAN SPACE RESEARCH ORGANISATION 114, avenue Charles de Gaulle. 92522-Neuilly, France Proceedings published by ESRO Scientific & Technical lnformaiion Brancr c/o ESTEC. Noordwijk, Netherlands Editors Bruce T. Battrick Nguyen T. Due Layout Simon Vemieer Printed by ESTEC Reproduction Services. Noordwijk, Netherlands FOREWORD The Eighth ESLAli Symposium, organised hy the Space Science Department (formerly ISI.AU> of the European Space Research and Technology Centre. iijs held at LSRIN. (•"rascal i. Italy front 4 - 7 June 1974, More than 70 scientists, mjmly from Europe and the United Stales. ,iitended to report and discuss recent advances in the slud> of M II Regions and the Centre ol thefialaxv. As ti eniioned hy Dr. Trendelenburg in his introduction, the significance and unexpected nature ol many recent infrared observations make these Topics of particular interest now., in view ul IV possibilities winch may S.KIII exist for infrared space observations. It is already clear lor example, that the need for higher spatial and spectral icsoluiion m the far infared may not be fulfilled until large telescopes can be operated for extended periods in space. Some of these possibilities were reviewed and discussed informally at the end ol the symposium when a bnef summary of ESRO's infrared mission definition studies was given. For tie most part, however, the symposium was devoted to the presentation and interpretation of results already obtained using ground-based and balloon-borne telescopes. The programme was also by no means restricted to the infrared region of the spectrum, but was aimed at a heller understanding of the nature of these objects through the combination of optical, infrared and radio data. Papers were also presented on related topics: such as molecular clouds and slar formation. I wi/iid like to thank everybody who participated in the symposium and the many people within the Space Science Department and ESRIN who helped with the organisation. In particular, the help throughout of my colleagues in the Astronomy Division and the efforts of (i. Neugebauer, D. Lemke, D. Dowries. J.M. Greenberg. R.E. Jennings and M. Harwit to control the proceedings as session chairmen wer». greatly appreciated. I wish also to acknowledge the invaluable assistance afforded by the Scientific and Technical Information Branch in producing this volume. I hope that the resulting collection of papers presented here will prove useful not only lo those who were present, but also to many who were not. A. P.M. Moorwood IJM ol Pat I lei pant s Inii< 1 GALACTIC H II REGIONS II OPTICAL OBSF-RVATKINS Die Oiwii Nebula. A phulngrapliti. suid> tit spatial Mruciiirv T K I.L.II Optical ..h nerval m us nt a lew situll II II rcpom deieclvd JI II Manciïaiie Loitcl/uckeriTiann NG( 7 Optical, infrared and radio tihservatioii!. of two II 11 repnm MJ. Barlow, M. Cohen A. T.K- Gull 1.2 INFRARED OBSERVATIONS Compaci infrared sources associated with southern il II return Jay A. Frogel & S. trie I'erssoii Infrared observations of NGC MM K.L Becklin & G Neiigehauei Recent observations nf the 8-13 pni spectra of H II iccions D.K. Aitken. B. Jones & J. Penman On the structure ut* M17S CD. Andriessc & J- Koomnuef Wide beam measurements or H II regions in Ihe infrared D. Lcmke Far infrared photometry of H II regions I. Furniss. R.E. Jennings & A.F.M. Moonvood IV T.K. (it'LL t:ai infrared observations of W51 and the Galactic Tenue J.A. Alvarez, I. Eumiss. R.E. Jennings. K.J. King & A.F.M. Moorwood High-resolution maps ,it H II regions JI far infrared wavelengths G.C. Fazio. P.E. Kkmmann. R.W Nnyes. E.L Wnglit. M. Zeilik II & KJ. Low W.« in the neat tnlrared V. Beet?. H. EUassei & R. Weinberger Observations of W3 in the 40 • 350 fim band I. Furniss. R.E. Jennings Ji A.F.M. Moorwood 350um mapping observations oi"M42 and Sgr B2 M. Simon 1 mm observations of II M regions. P.E.Clegg&P.A.R. Ait U GENERAL DISCISSION 1.4 RADIO OBSERVATIONS AND STRLCTLRE OF IIII REGIONS New observations of H II regions ji 875. 15.5. 31.4 or tv5GHz Hugh M. Johnson High-re solution radio observa lions of ihe sources near K3-50 Stella Harris A high-resolution stud> of the H II région W3 (OH) R.H. Harten Radio recombination lines from carbon and heavier elements from the direction L Hart & A. Pedlar Formation of H II regions by BQ radio stars with infrared excess F. Cialii &. A. Ma m m an o OH and the earliest evolution of H II regions HJ. Habing An empirical model for the structure of the Orion Nebula Bruce Baliek, R.H. Gammon & R.H. Hjellming 2. H II REGIONS IN EXTERNAL GALAXIES Nuclei and H II regions in spiral galaxies: Preliminary results for M10I P. Benvenuti &. S. D'Odorico Observations of the dwarf galaxy and IIII region II Zw 40 W. Jaffe, G.C. Perola & V.. Tarenghi i. I JUST IN H II REGIONS evolutionary clHiraclemiiti of a himodal grain mi>del J Mayo tireenl)crp & Seung Sou Hong JXiM in M II rcpuun Nino Panagia Ionisation structure and transfer of radiation in dusty nchulae Valic Peirosian Expected far infrared polarisa lion of H H regions and llic nuclei of galaxies Marlin Harwit Calculation of infrared spectra frum dust in planetary nebulae l;. h'pehtein, E. Ilussoletti & J.P. Balutcau The dusl-U'-gas ratio in the Or tun Nebula M. Perinolto & • Patriarch) Dust and gas within the association Cyg OB2 H. Elsâsser&K.Voelcker 4. MOLECULAR SOURCES AND STAR FORMATION A new infrared complex and molecular cloud in Orion I. Gately, E.E. Becklin. K. Matthews, G. Neugebauer. M.V. Pcnston & N. Scoville Formaldehyde line emission at 4.8 GHz near NGC 7538 D. Downes & T.L Wilson CO emission associated with Sharpless H II regions Dale F. Pxkinson, Jay A. Frogcl & S. Eric Persson CO mapping of 100 fim sources associated with dai* clouds: preliminary results M. Simon & M.N. Simon Star formation and contraction/fragmentation problems A.P. Whitworth 5. THE GALACTIC CENTRE REGION Dust in the Galactic Centre 221 J. Maya Creenberg & Seung Soo Hong Map of the Galactic Centre region at 2.2 pm 227 E.E. Becklin, G. Neugebauer & D. Early I lu-.!.milium 10- .'(l fjtit siiiiiiv in llu" (•aLutti" (Vnlrr .' Ht'tjintan.J K.v.mm-el A \1 .ie Vtk". MuliuoUuir UMNtuuM |>lu>!..iiu-m ol th.- Cibtii.. (Vnnc tei U. Oiih.-i IIIil u red ud uU llu-(..ibcii. < 1-ntn- H \ii, .hie " K J ,.+. 1> l> ::: ," Ohwn.. )••!!-.>: IÏI-JÎUÎ l.y.ii.wn m ilk- icami ,>55" v l" v in". -"•. 1>"- K I l oi-cii \ \ IV.:IJI Intense MINJ^-M'OT.J «ru.l.ir» m sin- (,J1JI-IK ( emir Bru^c fc-liek, &. R.-S-ri L Br,™.:i l-\jv.viv-j nilrjieJ liHtlccuiji- liiu-v (runt the Citovtu. CVtnii" 1 lluv.<«]ein LIST OF PARTICIPANTS i'liyiics Department y:ecn Mar> t ullcp: Mile hnd Road I .on(ion I: t I-nftland. iX'pjntnenl »l Pliysics and Ann tintvcriil} Colleec London London Wf It- (,B[ Lngjand Kapteyn 0hserY3lury ft) Box 800 (ironingcn The Netherlands l.'mvcrsitj Ji Tunni Italy Heard of Studies m Aitmnoim JIIJ ,' Lick Observatory Lnivcrsiiy ot Cahfom.a Sanla Cta/.Ca. (SA (iroiipe Infrarouge Spaiulc Mcudun Observatory •>; Meudon I: ranee Osscrvatorio Astronotnko di Roma Rome Italy University of Sussex Astronomy Centre Physics Building Brighton BNI °QH England California Institute ul'Technology 1201 E. California Blvd. Pasadena, Calif. 91109 USA Astronomy Division .Space Science Department ESTEC Noordwijk The Netherlands Oscrvalorio Astrollsico di Asiago University ofPadova .16012 Asiago Italy VHI H.'tcnun. J KJ, .oxiidhv;•n;il - Mi •iiMnecwvi: :u K< 1M CNR OMorvauwii' ASUI'IISR-O di ASIJJIO 3«M)i: AMapo Kalv (ïepg- P Queen Miry College Physics Department Mile fcnd Road London El 4NS fcntJand CNR Laboratory di Astrofisica Spa/iale CP67 r-rascali llalv Max-Plack-Insmui furemraimestristhe Ptiysik 804t> Catching bei Munchen Germany Max-Planck-lnstilut fut Radioastionomic 53 Bonn Auf dem Hugel 69 Germany Duinen, RJ. van Department of Space Research University of Groningen Poslbus 800 Groningen The Netherlands Max-Planck-lnstilut fur Astronomie Heidelberg Germany Department of Physics and Astronomy University College London Gower Street London WC I England / Otoiipc Infrarouge Spatule Mcudnn Observatory Osscrvalonu di /«rcctri Urpi F.. Fermi 5 50125. Firen/e Italy Fcuvrhaclicr. H Astronomy Division Space Science Pcpartment i:M"K \' AMr.moim Dindon Space Science Department ISTH VmriJwijL Tlie Netherlands Harvard College Observatory Cambridge Mass. 0:i.in USA Stale University of New York al Albany Albany N.Y.12::: USA Sierrewachl 8 Kaiscrstraat 57 Leiden The Netherlands Mullard Radio Agronomy Observatory Caver.oj'h Laboratory Free School Lane Cambridge fcngland Cornell University Space Science Building Ithaca. NY 14850 USA MjvrijiKklnMiiul lui t\irai"i MMi'dj-ihitij: l'ci Mini.l i-n Asiti'Hi'im IMIMKII Spa^f Soiciiif IX-pariiin-tii isn< Noordwiik The Netherlands l ntvcisitc de Mons I>epanement JAMiuptuMijui !°A<.eniicM;mtriju ~0l>0 M^HIS Belgium Stem-wairlit h K ai arrimai 5" Leiden The Netherlands Departmeni of Physic and Astntnotm University College Lnndnn London WClboBT bngland Lockheed Missiles jnd Space Co Department 52-14. lildg. 202 3251 Hanover St. Palo Alto. California W304 USA Departmeni of Physics and Astronomy University College London Gower Street London WC1E6BT England Astronomy Group Imperial College 10 Princes Gardens London SW7 1NA England Max'PIanck-lnstitut fur Astronomie D-69 Heidriberg-Konigstuht Germany Département d'Astrophysique Fondamentale Observatoire de Meudon 92190 Meudon France f -\MruriMim (Jivnmn Sp;i« !.viviKt Department I SIM S.».iil*ilk [he Nt'thrrUnOs AMMIlorm (rrnup Imperial ) n!lcge 1(1 Priiuf. danlrriv London SW~ ISA f-nglaml AMinptijsual (lhscnj:..r> .ïMli;. Asiajw lUlv I uri.K Naiuirul ,ic IJ Ri-Ju-f^i-.- SLientili<|ue Institut J'AilrnphiNKjut- I nitcniiede Licfit w-v:w>('«ime-Oiii£T« Jicifcium Ma> t'biick-Iniiilut fur fc*liatcrri'MiiM.iit: Phvsik X04M,jrdimj: hci Mum.hci> (icrm.Hn Milne. I) KatliophsAic* Lahnra!i California Institute of Technology' 1201 E. California Blvd. Pasadena. Calif. 91109 USA Astrophysical Observatory University of Padova Osservatono Asiroftsko 36012 Asiago Italy Department of Space Research University of Croningen PO Box 800 Groningen The Netherlands XII ftcini. 1 IjhmaiorU' Asiri'Vna Spa/ijlt* CP *:. (Kl(M4 l-'iawali HJK Laboralono di AMmi'iMi'a Spa/ia CPn™. OOOM Fravati ltal> NKAL.Jodrell Hank Ni Macclesfield. Cheshire \sHoph>MvJ Ul'^rvaiiti> ,it An Ijrcn h lormi 5 lulv Center U» Astrophysics • Han-ar«* College Observatory tfl Garden Si Cambridge. Mass 0,1 -Is ISA Kayal Greenwich Obstfrvjton. HaiUliam. Sussex England Stanford Universiiy Institute lor Plasma Research Slanfoid. Calif 44105 ISA Philips. J.P. Astronomy Croup Imperial College IP Princes Garden* London SW7 England Max-Planck-Instilul furEttraierrestrische Pliys:k D-8046 Carching b. Munehen Germany University of Cromngen Posibus 800 Groningen The Netherlands ETH Zurich Solid Slate Pliysks Laboratory Hônggerbenj CH-8049 Zurich, Switzerland CNR Laboratorio Plasma Spa2k> Frascati Italy itepartftlenf "t 1 ailh JTU! Span MJII- IrmcrsiU <>l Vu. V"rk Sli.iiv Uitw.kNV ISA Max-1'biKk-Iitiiïîu! »ur Attfttfr '.''. Ilc.ddherjf Kumgituhl lala Insniulc ni F undaincnlal Research H.imi BhahhaRujd B. nihay 4O0OH5 Indu 'icnJck-nhurg. I; A Space Science l>epartmeni fcSTM" NtmrtJwtjk The Netherlands Laboratory di Aitmfisua Spa/ule CP&? 00O44 I: i aural i Italy Voges. ft Max-Flanck-lnstitul furExiraiertesiruche Physik 8046 Girchmg b. Munchen Germany Autonomy Group Imperial College 10 Princes Garden* London SW7 England Sterrewachi 57 Kaiseniraai Leiden The Netherlands Aslronomy Division Space Science Department ESTEC Noordwljk The Netherlands Center for Astrophysics HCO/SAO 60 Girden Street Cambridge, Mass- USA XV INTRODUCTION ('housing topics lor our annual symposia is never easy, hut this year it proved to be particularly difficult. On the one hand rhîs was our last chance to review the current status of (•umma'Ray Astronomy before the launch of the C'OS-B satellite next year while, on the other, we were very much interested in giving attention to recent results in Infrared Astronomy at a time when there is much discussion within KSRO on the possibility of future infrared space missions. Rather than compromise these two ends of the electromagnetic spectrum we decided, for the first time, to hold two symposia and to have one following immediately after the other for the benefit of those people who wished to attend both. Three years ago. when we were only just beginning to become involved m infrared Astronomy, we held J symposium in Noordwijk devoted to infrared techniques in order to assess the technological problems involved in infrared space astronomy. The question I posed in my introduction then and the theme of that symposium was whether Infrared Astronomy would eventually move into the field of space research. A number of problems, particularly in the cryogenics area, still remain to be solved. Much progress has been made in the meantime however and the question now is not so much whether, but when Infrared Astronomy will move into space. Serious consideration is already being given within tSRO both to the planning for an infrared-astronomy satellite and to the possibility in the 1980"* of operating large infrared telescopes on the Space Shuttle. Within only a few years, therefore, we may have the capability for carrying out infrared observations for extended periods and free of present atmospheric limitations. To be in a position to best utilise the advantages of the space environment, however, we must remain closely aware of the progress that is being made and will continue to be made through ground-based, aircraft and balloon observations. Tim progress has so far been extremely rapid and has already had considerable impact in many areas of astronomy. To try and cover all the recent developments in Infrared Astronomy, however, would have been impracticable in a symposium such as this. W« limited ourselves therefore to the important topics of H U regions and the Centre of the Galaxy which have been much studied in the infrared during (he last few years. The results obtained have, for the most part, been both unexpected and surprising and clearly demonstrate the importance of observations in this region of the spectrum. ï XVI It i> jKo vk.ir (li.it \\w ri'-u!ls ol Inlr.iKtl \-lroiu>iii\ ...inii.it lv IIIM,USM\1 ni MII.IIIOH, IMII IIILM Iv ntli-rpri'lrii jlmij; -.villi . June W~4 1 A In-rnMi-nt'iiti; 7 1.1 Optical Observations THE ORION NEBULA A PHOTOGRAPHIC STUDY OF SPATIAL STRUCTURE T R Cull Kill Peak National Observatory*. Tucson, Arizona. USA iReadby B Balick) ABSTRACT Tlic structure of the ncutial and ionised regions continuum. Ha + |MI]. |SII|. and H£ exposures. of the Orion Nebula is described as recorded on direct The geometry- and variations of the structure plus photographic plates through selected interference fil polarisation information leads to the conclusion trut ters. Seven of the plates, which were exposed at the much of the outer region of the Orion Nebula is re prime foci s station of the Mayall telescope, are repro flection nebula. duced here. Differences in structure ate noted in the I. INTRODUCTION The Orion Nebula (s M42 = Orion A Balick, 1973; Zuckerman, 1973; Balick, Gammon & s NCC 1976 + NCC 1982) holds a very important Hjellming, 1974]. All suggest that the trapezium stars position in the study of diffuse nebulae. At optical have formed on the edge of a dark cloud, which in wavelengths, it has a very high surface brightness lum contains an infrared nebula at its centre. Details compared to other nebulae; little foreground obscura of the structure of the emission nebula are shown to tion is apparent Therefore relatively short photo depend upon the neutral gas distribution at the graphic exposures are necessity for small focal-ratio boundaries [BaEck, Gammon &. Hjdlrning, 1974], telescopes to record emission at a given wavelength. Good, high-resolution photographs, which record Even more importantly, the dark cloud associated mono-ionic light from the ionised region and reflec with the HII region is known to contain a bright ted light from the neutral region, will go far in ex infrared nebula and molecular clouds which have plaining the relationship between the ionised and been delected at radio wavelengths. It is essential to neutral media. understand the relationship between the dark cloud In Section 2, observations of M42 that have been and tue ionised region. obtained at Kitt Peak National Observatory (KPNO) Several empirical models of the Orion cloud com are presented. Monochromatic plates were obtained plex have been discussed in the literature (Terzian &. at the prime focus of the 4 m Mayall telescope through the use of interference filters. Seven plates of * Operated by the Auodatiori of Univenitici tot Research M42 are reproduced in Figures 1-7 and are the prim to Astronomy, Inc., under contract with the National ary source for the discession in this paper. Also in Science Foundation. cluded is a brief description of data obtained using other interference fillets m combination with image noted These regions include the core region, the intensifier? and an electrographic device on the two inflated source, the bar structure, a how wave, and "I cm telescopes at KPNO. Preliminary results ol the the tiutet filaments. tat 1er data are crucial to the discussions in Sec I inn .1 A summary is made in Section 4 of the discus The structure ol the Orion Neh.ila is also dis sion. Jilt] the present data ate found to be hesi c\ cussed in Section ?. Comments on the overall struc plained by the model proposed by Balick. (iamnion & ture are nude and specific re pun s ol mieresi aie Hjcllming |1*>74|. 2. THE OBSERVATIONS Most of ihe Jala discussed here consist ol se lecied duced in hgure 1 wis iccoided ihrough an Rli-dlO direct plates obtained at the prime locus station of filter and has a net bandpass extending liorn hlOO tu Ihe 4 m Ma.aJl telescope recenlK dedicated at Kill ™ 1IXI A. Exposures reproduced m Figures 2 - 7 were Peak Reproductions ot" these plates are found in made through 100 \ 100 mm interference filters Figures 1 through 7. and details of the individual ex specially selected for the f!2.7 beam. Each filter has posures aie listed in Table 1. The exposure repro a I.5'< bandpass (full width at half-intensity) and Figure 1. The Orion Nebula: wavelength range \61Q0 to 7100 A, filter RG-62. Eastman Kodak 09842 emulsion, 2 mm exposure at the prime focus of the Mayall telescope at Kitt Peak National Observatory. Original plate scale 18.6"/mm. PHOTOGRAPHIC STUIIY Ctf SPATlAI STRCnTURI- IN WMfjN T»bk I IgilrC Tiller LlRht hKfWiSI hitman numher designation bandpass Kodak emulsinn 1 RG-6IÛ A6100 • ""OOO A 098-0: kbfOO Contmuum ow-o: .1 \hizs IS Hi tm-02 4 A656.Ï Ha*[NH|ï6548A} o>J8-o: t[Nll](h5MA> S XM70 Continuum OTS-O: b A4M6I H0 Ib-U 7 A4770 Continuum ll»-0 Vie Ovm Nebula: continuum « \6900 A through m 90K wide filter full width at half intensity (FWm).BtarnmKodcktiao^2tntdshtt,Mrnhteja!osure(tetf!t.l/. i-.insfets ol three prniuiu cavtliex The iciecliOTi . il- «ai> n( this ghost image is less than ?* ot the total side the bandpass is prcjlcr than 10* ltt>m ulliaiiohM vtellai energy and prows (o t*e negligible Tor nebubi lo mi'iared «awlengtlis. Three ni IIK* filtcts transmit structures t-asiman Kodak lla-O and (Nh-lt; emul only continuum taJution centred on A4"*"'0. JM'l). sions w-etr used for this series of plaies Hie aiithoi and Xh<*00 \ Wlien placed in the 1 : " telescope has anolher series of plates with Ilia) and l^ur beam, thtee other filler's ate centred upon Uii emulsions The latin series, although having much CUSt-.] A). Ha <\(.5<..= M ' |NH| iXfrMS* hetlcr resolution and signal-to-nnise ratio, pioved to XeôS4Ai. and |S1I| i.\b~I~* .\(>".M Al The uni- have too much cuntiasl for reproduction All plaies Iomiii\ ot transmission lot a given emission litte is have vensitomeier calibrations foi future iso-mieiis»y within 5 - across each filler contour mapping. Tin* seemc diameter ol the >iellat images on the Mates w«« also recorded of \\A2 using narrow plaies is I" - 2" tot Unit sure Howevet. the densest bandpass interference filters These filters, laiipnp. in slat images show a 10" diametei halo which is due in bandpass from o in 20 A, were limited to use al ihc internal reflections within the filiei and is not cor l>2cm telescopes with focal ralios of F/".S and rected by antiretlecimn coatings. The relative inter- F/I.V5. The Carnegie two-slagc image intensifier $> Figure 3. The Orion Nebula: jSllj (K67I7+\6731 k) through a 90 A wide filter (FWffK Eastman Kodak 09842 emulsion, 6 min exposure (see Fig. I ). i'llUKKltUrilk SII'llV (il SPAflAI. STKUTIW IS UkttiS *( U I »;i» Mved nt tc*.i«d mtw-ftmic irtmftei *ll) and the Kmn tameia weie used in reu>id the pi>lan- (.\.n;7At and |>7.*:5Af, fO l| IXM(K)A), |S llj «atum data. 7he platen are calibrated and vmc have (Xf.7^Ai. fN 111 Uft SM A>. and «itiei W3*denjala been Manned with a PÎ>S mK«»knst''>meier is» HnxomeUtL.- data of Ifcl i.X4X<>) A), continuum ai uilensity and line iati«> ointuur*. have heen mapped iM^O A), ami other bgndpasve* were retarded usmn In addition, polarisation data arc bemp mapped AH j Kmri rlectnipiaphic camera In addirum, pulmiu- • if these maps will he published in the neai tutuic nun evposum have been rccoidcd using a Polaroid 3. DESCRIPTIONS ! X THI- OVERALL STRUCTURE the vtsibfc riches. The broad-bandpass red exposure (Fig. 1) shows relatively diffuse, low-contrast struc Several generalisations can be made concerning ture throughout the nebula. The general structure for 7Tte Oliun Nebula: Ha {\656J AW A7 /// (\6S84*\654S A) thfough a 90 A wide filter (FWHl). Eattman Kodak 098-02 emul$ioti, 2 mn exposure {see Fig. H t» [K (lULL Fiettre S. The Orion Nebulg: continuum ti \6470 A through a 90 A witte filter (FWHfl, Eastmtn Kodak 09842 emulsion, 30 mm exposure /see Fig. 1). all of the continuum exposures, the Hp\ and the Ho + |S ID06725 Ah and |01] (*6300 A). We call this to |N II] exposures (Figs. 2, 4-7) is also diffuse. How attention because Wurm & Rosino (1959, 1965] ever, there are some exceptions to this generalisation found that their monochromatic photographs were that will be discussed below. The |S II] exposure very similar. The difference m results might be ex (Fig. 3) is very sharp in structure. Even in the core plained by the much broader bandwidths of the fil region, much structure is seeing-Urnited. In nearly ters used in their observions. Wurm & Rosino used every case, sharp structure in [SII] is correlated by liquid Filters with 150 • 200 A bandpasses (nothing is more diffuse structure in Ha + IN II], Hp\ and on mentioned in their papers concerning rejection out occasion with continuum emission. side the bandpHi). The bandpass» of filters used These generalisations can be extended by refer in the present series of exposures are well-known. Our ring to narrow-bandpass exposures not reproduced measures of continuum and HP- from the electro* here. Most structure is diffuse for the hydrogen tine graphic plates, concur with measurements made by exposures. He I (XS876A). |Olll) (X5007 A), and Sniffer A Mathis [1974] using a grating scanner. It is continuum throughout the spectrum- The sharp struc found that, within the central 20' diameter portion of ture is usually ssen in all of the following lines: M42. the continuum relative to Hp* increases from I |011) (X3727 A) and (X7325 A), [N II] (X6S84 A), (com 4770 A) 3: 700 A = l(H0) at the brightest part PHOMM.KAI'HK STl'UY Oh SPATIAL S1RI I'll Kf- IN (JRIOS figured. The Orion Sebula: H9(\486I A} through a 60 A wide filter (FWHI). Eastman Kodak IIa-0 emulsion, 10 win exposure (see Fig. II of the nebula to I (cont 4770 A) ^ 20 A continuum = lines is seen in Figures 6 and 7. The H0 and con I(H0) several arc minutes to the northeast. Correc tinuum (X4770A) exposures (Figs. 6 and 7) were tion of these mesures for the relative continuum dis recorded for an identical length of time ( 10 min). The tribution with wavelength |0 Dell & Hubbard, 1^64; continuum emission with a 60 A bandpass is nearly as Simpson, 1973] suggests that the continuum contri strong as Hj3 in the rim structure extending from bution through a 200 A wide filter centre at 6725 A northwest to southeast. could be as strong as the (S II] contribution in some One further comment must be made concerning parts of the nebula. Indeed, a difference in diffuse [Sll| compared to other exposures. All of the nebular background is seen between 90 A bandpass narrow-band exposures except [SU] become over |S It 1 exposures and 8 A (X6731 A only) [SII] ex exposed in the core region if detail in the outer region posures. It should be noted that the continuum is to show up. The |S II] emission seems to be emit X64TO and X6900 A exposures (Figs. 2 and 5) are for ted from a shell rather than from the total volume. This 30min and the [SU] exposure, although exposed implies [SII] is emitting more from an outer shell through a filter having the same bandwidth, is for structure than from very small condensations only 6 min. By comparing these two plates and throughout the total volume. This argues against a plates taken for similar exposure times, it can be con uniform distribution of condensations throughout the cluded that most of the structure seen on the [SII] nebula. Velocity studies comparing fS II] motion to plate is due to (SU] emission. Further evidence on [OIII|, Ha and [Nil] motions should be done to the relative intensities of the continuum and emission detect systematic differences, like the studies of Figure 7. Vie Orion Nebula: continuum (\4770 A/ through a 60 A wide filler (FWHI). Eastman Kodak lla-O emulsion. 10 min exposure (see Fi/t. I). Fisher & Williamson 11970J. Wilson et al. 119591. behaves very differently with ionisation. Ratios of and KalerJ 1967|. |OM]/|OIII| and |Oi|/|Oll| increase to the cast Several interesting regions will now be discussed. across the bar-like struciurc. In the 10 I ) emission The reader 'j referred to Figure 8. which is a pencil line, the bar-like structure is nearly as bright as the drawing indicating the specific regions of interest. brightest part of the nebula. However, HajHjî ratios do not change across the bar structure, but contin uum to H0 increases with distance from 01 Ononis. 3.2 THE CORE REGION The conclusion is that the bar structure is an ionisa tion front of the dark cloud behind the ionised Structure of He 1, [0 JI1]. lia, Hj3 and contin region. uum seems to be very similar. All tines and contin The dark bay structure located to the cast of the uum emissions are peaked at the same position to the Trapezium is presumably to the foreground of the west of the Trapezium. However, the boundaries of ionised region. Here the ratio of Ha to Hp* increases, the core region vary differently and tell us their rela but varies throughout the bay, as this cloud seems to tionship to the neutral and ionised medium. The be very clumpy. There does not seem to he much structure noted here has been described by Wurm & ionisation structure associated with edges of the dark Rosino |19S7|, who discussed structures viewed cloud that is notable from the photographs, or from through much broader bandpass filters. The emis I01l]/[OHI| and other line ratios. sion-line structure at the boundary near 02 Ononis The boundary extending from southeast to north- I'HOItM.K At'HK ' 1)1 Ml SPWIAI MK! ''M HI IN OKI' west oast (he dark ha* is dm- t<> a pari •f the continuum HIL read's Mote over, certain iealures. espeuallv Much structure which shows up in |S l!| is pre .1.4 THK BAR fcXTfcNSION sumably due to high-density cluups bathed by a strong ultraviolet radiation field. Most struclure Is The bar struclure to llie southeast of 01 Ononis presumably intimately related wuh the ionisation has an extension which is most noticeable in [Sll| front which is eroding the dark cloud to the back ot and continuum at (AM70A) I Pigs. 3 and 5). This the nebula. However, many features show up especial feature is peculiar because it is one of the few sharp ly in |S II] that are suggestive of local gas motion. scrutinies that is noticeable in continuum on this The first feature is about 4' due west of 02. series ot plates. In |SMJ. the extension proceeds Orionis. It appeals on the |S 11} plaie if-'ig. 3i a.-, a several art minutes to the southwest, then becomes bow wave with a star near the centre oi the rim. It diffuse and splits. The continuum feature becomes looks sufficiently peculiar to seem to be a plate flaw. complementary to the JSII] structuie and very dif However, it can be found on 110. Ha *• JN II) plates, fuse. The two (S II j structures may extend far to the and also on an [Oil] plate published by Wurm & noriliwcst and to the southwest. Both features then Rosino 11 U5(M. One suggestion has been that this is a appear u> join the western rim, which contains very bow shock wave (Theys. 1°74|. brifjit filaments in the lower ionisation lines. The second feature is an apparent bubble in the This bar extension is evidence that far beynnd the western region. A thin circular shell is seen in Ha + cure region, there is an ionised region thai is inter |N II). H|? and [S 11]. A star is projected within the acting wiih the background dark cloud. The ulira- shell to the eastern side of centre. It can be suggested violet radiation has sufficieni intensity and individual that this is a bubble-like structure associated in some photon energy at the ioniscd-neutral boundary to way with this star. 10 TR «I'll The core region shows mui.li ordered structure in 'seen in Ha. lias a very strong structure that is comple |Slt| emission. The direction of the long, ihin mentary to |OII|. (NII|. and |SII] This com streamers is not radial with respect 10 the 1rape;ium plementary component is identical to the continuum stars, but appears in be distorted by the dark cloud tenures. structure. Streamer, to the north ot the Trapezium It a very peculiar that (O 111] A5007 A structure ate extended m a northwesterly direction is so similar to continuum distribution, and dissimilai to the lower ionisation features in the ou'er regions Ilowevet. polarisation data published by Hall [ l*>74| .Vu CUMPU-MrNTAKY STRICTURES yield an explanation. Measures were made of polarisa tion through four filters isolating continuum and Variations of continuum to Ho emission were through four filters isolating Ha. 110. |OIII| noted by Pennotto & Wurm ll**7'I- Tney noticed X5007 A and |OII] X37r> A. Polarisation of contin- nearly complementary structure when comparing uum radiation typically was l'ï near the Trapc/ium. lia * JN II) to continuum photographs. This effect is but increased to above 1(K at 10' distance. The confirmed and even more peculiar effects are noted. polarisation of the emission lines was found to be The photographs of Ho * (Nll|. |S II]. and contin smaller or comparable to the polarisation of the con uum (Xb470 A) (Figs, 3-5) show reversal in relative tinuum, especially far the |0I1I| A5007 A emission intensities in adjacent structure throughout the enure However, the hydrogen lines, and especially the regiun. This effect is most noticeable in the southern |0II] X3727A emission line, were nnt as highly filaments. All continuum exposures show the eastern polarised. One possible explanation for this differen filament to be much stronger than the wesiem fila tial effect suggests that [OUI] is emitted from the ment. The relative intensities become equal in the central region and scattered al a great distance. How Ha + [NII] exposure wd are dramatically reversed in ever, (Oil] is emitted from an outer shell region, the [S II) exposure. Spectra of this region confirm whkh is much closer to the reflecting cloud. Thus, this effect, but with one added feature: the |0II1| the scattering angle would average over larger ranges and other highly-ionised atomic lines are more intense in angles for |0 II] emission than fur {0 III] emis in the eastern filament. Visual inspection of the spec sion. tra suggest that the emission line strengths or the The polarisation measures using the Kron electro- western filament are very similar to the emission line graphic camera agree with the suggestion that the strengths of the core region, yet the highly-ionised outer pans of the nebula are highly polarised, but emission line strengths are very weak in the eastern these measures arc presently only in continuum. Al filament. The eastern filament has H0 stronger than though the polarisation measures do not go beyond |011l| X5007A 10* of 01 Ononis, the upper portion of the eastern There are complementary features in the western filament proves to be at least I OCT polarised, while rim structure, which are most noticeable in compar little polarisation is measured in the western filament. ing (he [S II] and continuum exposures. Narrower Therefore it is suggested that the (O 1111 emission, bandpass-exposures show that (NII], |0 II]. |S II], and other emissions associated with the outer portions and Ha are similar in structure, but Ha extends across of the nebula, are scattered light from the central the total complementary structure. However, The region. (0 III] emission, in addition to the diffuse structure 4. CONCLUSIONS The photographic data described here strongly and down to the southeast. Part of the cloud is also suggest that the ionised region known as the Orion to the western side as evidenced by the western rim Nebula is closely associated with the surrounding structure in continuum with complementary bright dark cloud. Ionisation structure seen moil clearly in (SII) structure. Polarisation measures previously {SII] suggests the neutral cloud is being ionised at mentioned confirm the relationship of the dark cloud the rear portion of the emission nebula even at Urge with the emission nebula. I therefore concur with the distances from the Trapezium. The continuum plaies empirical model of Balick, Gammon & Hjellming for show that part of the dark cloud loops across from the Orion Nebula. the northwest, past the eastern side of the Trapezium OPTICAL OBSERVATIONS OF A FEW SMALL H II REGIONS DETECTED AT INFRARED WAVELENGTHS Marie-Claire Lortet-Zuckcrmann Department of Fundamental Astrophysics. Meudun Observatory. France Several observational results I Bohuski. Dcharven^- shifted by a distant of the order of 0.1 pc from the Bauuel, Elliott and Mcaburnl on the density and brightness bound"y towards the obscure region. The bilplitncss distnbution across obscure lanes in small relation with !.. d sources is briefly discussed. (la nebulae arc discussed. The peak density is often 1. INTRODUCTION I wish to discuss a few new results pertaining to Persson & Froge)|1974]of optical and infrared data the small-scale structure of the ionised gas in small obtained on K3-50 with 3" resolution. They conclude H II regions. First two general remarks. thai, in this area |0.13pc x 0.13 pc at 9 kpc). fine A small H II région probably never exists as an structure exists, so that it is not safe to identify as isolated object. Il always appears to be ionisation- one and the same object the different sources ob hounded somewhere (if not all around) and thus to served al different v/avelengths. We may wonder what be physically associated with clouds of neutral gas are the ultimate structural scales that we shall find, and dust: these clouds, in turn, are often rather and how far we are now from a correct understanding exlended and massive and contain other optically of the observations. visible nebulae (reflection or emissive nebulae). The We should keep this point in mind each time we most typical examples are Orion and the large com discuss an observational result, especially a density or plex of W 58, which contains the now well-known radial velocity measurement or the identification of compact H II region K3-50. two sources found at different wavelengths. The second point is that, as our knowledge im i would now like to turn to a special case of proves, a smaller scale structure is revealed for each small-scale structure, namely the small structures and object of the complex. Going on with the same exam the density distribution of the ionised gas. We shall 1 ple, this is illustrated by the recent discussion by deal with linear scales between 10" pc and HF* pc. 2. MONOCHROMATIC PHOTOGRAPHS OF SMALL H II REGIONS It is probable that the first picture of an H II realised in n-.ure. This has became increasingly ap- region as a homogeneous spliere of ionised gas is not parent from the high-resolution continuum radio 14 M\RII I I MKi KM H I-7U'K( KMANN cups |i-.(:. Isiaêï cl al.. 117_!| and new. non over liai objure Unci is sel by (lie jtmosphenc visibility; t\pt»sed monoctiituiiaik' plmlupiaphi see. lot in ihus niinn^K'ally it niay IK- much less llian ;" stance. Sli M 5c. Deliarveup-ILudc! 11 '>74 |, C \ nr! pc ai distance 2 kpe). In tins case, as in Sh 2-25>. 257. 2i>'>. l'hopiitei. Dclurvcnp A l.oiiei- numemus ollicis. the ohscure lanes or boundaries arc ZiicieiiiMiinjW?4|. ('ormncnliiic. only on ihe la*l nul essentially due to the existence of foreground nebula, the buneith-shaped nehula Sli 20ft1'. in dust. because a similar structure is ound at radiu- direct cvideiie* |Chopmet el al.. 1*>74| indicalcs tlial wjvelenpth (Israel, pu va te communication!. On the the ceniial Ma: is one ol the exciting ones. Il lies m contrary, the physical emineclion between obscure an obscure lane cio-Miip ilic nehula. An important icpious and inmscd gas seems lo be confirmed inde point to note is ihai ilie smallest scale of the hiiphi- pendently by the study of (he density distribution at ness inhoniopcneities le.p the boundaries of the ecu- the brightness boundary. 3. DENSITY 1M ST RIB UTl ON NEAR THE BRIGHTNESS BOUNDARIES Several authots have made a detailed sludy of the the slit of a spectrograph. The instrument procedures, densitv and brightness disiubutions in a nebula alone, nebulae and anpulai and lineai scales of integration Table 1. Studies of density distribution, linear restitution of the density determination Distance Anpulai and lineat scales Instrument Nebula IIIÏM UIIJCIII (kpt) laic s> (PCI Elliot &. Meabum. A Orion 0.45 .'» ; 0.75 x Iff' and 1973 1.75 x Iff' Bohuski. 1973 B MS 1.6 2\ Z l.&X Iff' IlioUTgJsSS) B M:O 2.5 5x5 61 Iff' Deharveng-Baudel. C Sli 2- 156 .1.5 = 8 0.14 1974 ditto C Sh2 157 3.5 6.3 0.11 Deharveng-Baudel, C Sh2-162 3.5 = 6 0.11 1973 Chopinet et al.. C Sh2-25S 1 8.4 4.2 X Iff' 1974 ditto C Sh2-257 1 8.4 4.2 X Iff' ditto C Sli 2-269 1.9 8.4 8.4 X Iff' A. EUiolt & Meaburn, electronographic image-tube spectrogrph dispersion 20 A/mm. Slit 7"x Ï B. Bohuski, spectrograph, dispersion 27 A/mm, slit 200" x 25", 50"/mm C. Deharveng-Baudel, spectrograph. 34 A/mm, slit 4.8" x 7', 847mm OITirALOHSIRVATIONSOI-SMALL Hll RIGIONS Tfif density tardes / and brightness in fSM/X 67 JI line distributions, for the spectrum 11IW of the nebula Sharp- less 26'}. The spectrum is taken Uighth south of the star m an east-west direction (see an ffj} monochromatic photograph am! the position oj this spectra, in Ch"pi- net et. al.. IV74J. hast is to the left The adjacent ticks in abscissa are 2u" Hi 2 pi to 2 kpc) apart. Vie position of the infrared source 1RS 2 is shown. Jtif uncertainty lies in the diffi culty m relating the Ity and \S III bright ness profiles, the infrared source may also be extended by 5"-IU". the density determination ts not very small (4 to 10 x I IT1 pc). except for Oriun. Sli 2-269 again illustrates very well the two more prominent results. Figure I compares the density dis tribution and the brightness in the 6731 [S II] line III (the line enhanced al higher density): la) Density and brightness peaks do not coincide: the peak density is shifted by about 0.1 or 0.2 parsec T—ii\i—ZWWIJU in the obscure region, 11 i1!; !• 'i (b) The density increases at the outer brightness -i—i—f-1—i—I,."'.** 'i boundary, perhaps similar to the bright-rim phe- notoenun. Moreover, a density increase is also found towards the central star of the nebula, where an abrupt brightness reduction is observed for tlic density determination arc described in Ta in the [S H| line and in H0 also. This same behav ble I. The density was determined from the ratio of iour is found for olher nebulae, especially in |S 11} lines AA 6731 and 6717. which is density de Sh 2-157 A (Deharveng-Baudel, 1974] between pendent (Saraph & Scaton. 1970], except in the case the eastern bright bar anH the exciting star. A of Orion for which Elliott & Mcaburn used the dou similar observation is made by Bohuski|l973] in blet [O IIJ AA 3726-3729. I have not included the an obscure lane of M 20, T6-S, which is similar to [S II) study of Orion by Wurm & Perinotlo[19731, the lanes shown on the Ha and |N II] photo because their spatial resolution is poor, as they were graphs taken of this nebula by M. Smith (1972] looking for a quite different scale phenomenon. (the position T6-S is slightly north of the field As can be seen from Table 1. the linear scale of taken by M. Smith). 4. RELATION WITH INFRARED SOURCES Sh 2-157 A has been studied by Betgeat, Lunel The spectral distribution is not known. Data of better and Sibille at 2.2^m (1974, in preparation], with a resolution are obviously needed. circular diaphragm exceeding 38". The beam was A second interesting case is Sh 2-269. A 5" - 10" centred on the exciting star 157-1 (Chopinet & extended source (1RS 2) has been discovered at Loriet-Zuckermann, 1972]. An exterded (30" -40") 2.2 urn by Wynn-YVjHiairo et al [1974 a]. This source source was detected, which might correspond to one is nearly coincident with an OH source [Wynn- or other of the two density enhancements previously WïUiams et aL, 1974 b] and is characterised by an described near the obscure region containing the star. especially blue slope between 2.2 pm and I ft urn 10 MARL! -CLAIRl l.ORUT-ZUCKfcRMANN where it was not detected. In position, it happens to present on the spectrum I 1109. The ptissihlc position tall on the spectrum I 1109 taken by Deharvcngng-- (and error bar) is shown in l;igure I. The infrared Baudel. although its exact location is difficult to source is not far from the density enhancement lo ascertain because the [SIIJ and Ha or H<5 brightnesesss wards the star, and might be physically connected distributions ate very different and no stellai objecti iis with ihe region of higher density. 5. D SCUSSION 5.1 LINEAR SCALES b.;en studied for nebulae otbet than Onon [Munch & Persson. 19711. For an intermediate-scale structure From Table I. we see thai the best linear resoluu' (?: 0.2 pc), the relation between brightness and redde- 1 tions were 0.75 * III pc for Orion |Ellioti & ning is not obvious: there are cases where the bright J Meabum. |Oll| lines] and l,6xl(T pc for M8 est wing is the more obscured, e.g. the bright bar in (Bohuski. |S 111 lines]. h may be significant that thie ShM5?A [Deharveng-Baudel, 19741. and other [OilJ line study of Onon does not reveal any syss" cases where the reverse is found to be true tematic shift between the density and the |0 It I I (Sh2-25Sl. 3129 intensity peaks. This may be due to the use ojf the oxygen line instead of sulphur lines, for density >' 5.3 DENSITY ENHANCEMENTS NEAR BRIGHT. determination. Cumulative effects may result i,nn NESS BOUNDARIES AND RELATION WITH IN- weighting the [Oil] lines towards regions of lesse!rï FRARED SOURCES density and higher nebular excitation than the [S II| '•' DciiMiy cithaiueincnU in legiufri of abrupt br.5i.t- ty exceeds 10* electrons per cubic centimetre, the 0+1 ness reduction are a frequent phenomenon. We here + ion requires more energetic photons than S , and emphasise that the density peaks may actually be charge exchange (Field & Steigman. 1971; Williamss-, higher than found by observation, because of the in- 1973] may possibly be important in order to reduce tcgration along the line of sight. In addition, there is the 0+ region near the nebula's ionisation boundary'•. the existence of density enhancements towards oh- However, the absence of peak density shift fo>rr scure regions near the star, a phenomenon that isap- Orion may also be due to the domination of a parently different from the bright-rim phenomenon. smaller-scale phenomenon smoothed out in the study* Finally, it may be significant that, in the two cases of the other nebulae. studied (Sh 2-157 A and Sh 2-269) a non-stellar infra red source is found at 2.2 jim close 10 the density peak. It might be suggested that a type of infrared 5.2 REDDENING source is directly connected with density enhance ments close to Ihe star and might possibly be charac- Hie small-scale structure of the reddening has not1 tensed by a relatively blue spectral distribution. REFERENCES 1. Bohuski, TJ-, Astrophys. J. 184,93 < 1973). 6. Deharveng-Baudel. L., Astron. & Astrophys. 2. Chopinet. M. & Lortet-Zuckermann, M.C., (1974). Astron. & Astrophys. 18,373(1972). 7. Elliott, K.H. & Meabum, J., Astron. & Astrophys. 3. Chopinet, M-, Deharveng-Baudel, L. & Lortet- 27,367(1973). Zuckermuin, M.C. Astron. & Astrophys. 30,233 8. Field, G.8. & Steijman, G., Astrophvs. J. 166.59 (1974). (1971). 4. Chopinet, M., Georgelin, Y.M. & Lortet-Zucker- 9. Israel, P.P., Habjng, H J. & de Jong, T„ Astron. d} irunn.M.C.^SJiroft. A. Astrophys. 29,255 (1973). Astrophys. 27,143(1973). 5. Deharveng-Baudel, L, 18th Internat. Colloq., 10. Munch, G. & Persson, S.E., Astrophys. J. 165, 'Planetary Nebulae*, liège, 1973. 241 (1971). NCC 7635 AND ITS STELLAR NUCLEUS Roberto Violti & Roberto Nc*ci Laboralorto di Astrofisica Spazisle, CNR. Frucatt, Italy ABSTRACT Observational results concerning NCC 76J5 are exciting star has an 06f spectral type. The emissions discussed with special regard to the infrared data. are probably variable, the line broadening corres Spectroscopic investigations made at the Asiago and ponds to a rotational velocity v sin i = 240 km/s. Dominion Asirophysical Observatories show that the We shall discuss in this paper the general proper the shel', and for the condensation, which displays a ties of NGC 7635, and investigate in detail the spec comelaiy-likestructure (Johnson, 1974], trum of its exciting star BD +60° 2522. An infr=:cj survey of the nebula is under way at Figure I reproduces two plates of (he nebula ob Asiago, and Rosino ( 1953| found several infrared tained in the blue and in the near-infrared with the stars, two of which, indicated in the figure by ciicles, large Schmidt telescope of the Asiago Astrophysical are the Mira variables MO and MP Cas. with periods Observatory. In these plates the bright condensation of 252 and 334 days, respectively, and an amplitude near the O star is in evidence. The roundish sheil dis variation in the infrared of nearly 3 m {Rosino & Di plays a filamentary structure: its diameter is about Martino, 19711. The infrared luminosity at maximum 3 pc, much largei than the ordinary dimensions of the is 1 = 10.3 m and V-I is +S.5. Both Mira stars may planetary nebulae. The diffuse H II nebula Sharp- well be the same distance from the HII region. less 162 has an irregular structure with bright rims This is not surprising since Maffei found several long and obscure regions; it should be noted that also period variables during his infrared surveys of the within the shell, to the south of the exciting star, Milky Way IMalTei 1967,1974]. there is an obscure region. On the other hand, BD +t50°2522, the exciting According to the surface brightness in HQ sur of the nebula, is itself an iafrared source (Cohen (Pottasch, ]965| and to the radio observations (Is SL Barlow, 1973). Apparently the excess at 10 and rael, Habing & de Jong, 1973] the total mass of the 20fun comes from the dust around the star, rather nebula is a few hundreds of solar masses; the sheQ has than the cometary condensation. a few MQ. Maucheral & Vuilkmin [1973] showed The energy distribution of Ihe stellar light has that S 162 and NGC 7635 have the same radial velo been derived by Doroshenko (1972| between 3200 city, about -55 km/s. The velocity of the star is more and 8000 K, and is quite different from that of a hot positive, as will be shown later; also the region inside star. This is also confirmed by the infrared photo the shell has a slightly more positive velocity. In the metry. Doroahenkothvutetfutthis anomaly could be infrared plate the whole nebula has disappeared, ex ascribed la an F supeigiant companion of the Û star. cept for a tenuous enuatton in the northern part of A more realistic poanbiKty, confirmed by the pre sence of the strong He II line in the yellow at 5411 A, * Supported by Centro Linceo Inictdiidpiiiuit, AccaAemii is that the star is surrounded by an extended atmos Nuionalc del Liasi, ferme. phere. R. vKiTTi A R NI sn • .* Figure 1. NGC 7635 in the Mue and in the near- infirmai. Large Schmidt telescope of the Attâgo Asiropttyskal Obtenmtory. The cmxied sun are the mfhwed Mint mi- ÈbksMOandJfrCàs.Northisattop. A spectroscopic investigation of Out ttar was car ponding to a rotational broadening of v sin i * ried on by ut at the Asiago Astrophysical Observatory 240km/i. Due to this effect, the last visible (middle dispersion spectra, objective-prism plates at hydrogen line is Hi4. the Schmidt telescopes, image tube spectra of the (iii)Two broad emission features of N III at 4640 A nebula) and at the Dominion Astrophysics] Obser and of He II at 4686 A arc present. Their equiva vatory (IS A/mm spectra, unfortunately rather lent widths were ZS and 1.0 A, respectively in underexposed). 1969, but arc variable in time; the He II line was The mam features that arose from this investiga absent in 1954. C HI, if present, is in absorption. tion assy be warisrd » foBows: (iv) There are broad «tscsleUar absorption features at (i) Tim arc lirosd absorption lines of H, He I, He II. 4430 A, and probably at 6280 A. NU, and OIU. The spectral type derived from (v) The interstellar Call and Nal lines are strong. me helium inec ratio is 06. The lane intensities The equivalent width of the K line is 0.8 A. The suggest that it is almost a Main Sequence star, Ca II radial velocity is -29 Icm/s. (fi) The mean line width is A>A « 136 x 10** corres (vi)The stefar radial velocity is very uncertain due to V,< 7f.iS AM) IIS STH.I AK the itifa width of rite Unes. The 40 A/mm snectia gave the following values m I "67 H * 3(11* i"lll:) Ile Î • î(4iinc>J Ik II +11 (IlmcM (-rom the high dispersion |>latcs. il wr possihk- m measure wnl> 11^ I 44 i 15 km/s), Hfi f*5 * :okm/s). and Hf | J 5 A 20 km/s derived from the tfacmjtsl These lines are blended w«h other ah««p- tion lines. I-iRiirc i shows a small portion of the spectrum near the 44 MS mietsîettar hand, the widlh of the iden- nticd ahsorption lines is considerable, and several itthcc absorption lines aie probably present, as sug gested by. Tor example. Underhill (l''nO|, but are lost in the plate noise. We musl put in evidence some similarities be tween this object and the it flection nebula NUC 7023. where the central star, HD 200775. is a B3 star near the Main Sequence that shows low exci tation emission lines (H, [Fell]), and is totaling rapidly [Vmtti, 1969]. This star also has an infrared excess. Other very broad absorption features are prob ably present in BD+ 60° 2522, for example near 4600 A; this could be the effect of many unresolved absorption Uses. In conclusion, ihe stellar radial velocity is a few tens of km/s more positive than that of the surrounding H il regions. The radia] velocity and the strength of the interstellar Ca II lines could be partly due to the presence of a cold cirrumstellar envelope. In this res pect, it would be interesting to study in detail the He ! lines arising from meiastable levels, like 3888 and. in the infrared, 10830 A, and to measure the interstellar fines in the nearby stars. BD+ 60° 2522 is certainly losing matter, as derived from the presence of emission lines, high rota tion, and extended atmosphere, but the raie of mass loss does not seem large enough to support the for mation of the nearby condensation and the shell. On the other hand, with a few tens of km/s of velocity, the star could have travelled (torn the centre of the shell to its present position in 10* - 10s yean. i.e. in a lime less than the mean lifetime of an O star in the Main Sequence. Hence, it could have been Figure 2. High-dispersion intensity tracing of the spectrum of BD* 60° 2522 between Hy and He 114542. The spectrogram was ob tained on 27 December 1969. witk the 72" telescope of the Dominion Asrro- phytical Obtenmtory. 22 K viorn * k si wi lotmeily the component nt J massive brum systemn., ejected during the explosion was slowed down by the whose primary evolved, transferred part of us mass to diffuse material of the nebula, and » now forming the the present 0 star, and finally exploded as a super•r- shell. nova. Then the system was broken, while the material ACKNOWLEDGEMENTS We arc grateful in Prot. L Rosino for suggesting k.O. Wnghi foi the observations at the 72" telescope this investigation, and for providing observational of the Dominion Asirophyskal Obscr-jlo'y. time at the Asiago telescopes, and (o Prof. REFERENCES Ï Cohen. M. & Barlow. M.J.. Astrophys. J ixtt. 8. Pottasch, S.R., Vistas in Astronomy 6 . 149 185, L37<1973>. (1965). 2. Doroshenko. V.T.. Astron. Z. 49.494 ( 1972». 9. Rosino, L. PubL Oss. Astron. Bologna VI. 3 3. Israel. F.P.. Habing, H J. & de Jong, T.. Astron. A (1953). Astrophys. 27.143 (1973). 10. Rosino. LiDi Marline. D.. Inf. Bull Var. Stars 4. Johnson, H.M.,,4Jfmn. & Astrophys. to be pub 585(1971). lished. 11. Underbill, A.B., PubL Dom. Astrophys. Obs., Vic 5. Maffei. P. Astrophyt. J. 147.802 f 1967). toria, Vol XI. No. IS. 283. 1960. 6. Maffei, P.. private communication. 12. Viotti, R.. Mem. Soc. Astron. It. 40. 75 (1969). 7. Maucherat. A. £ Vufilemin, A.. Astron. & Astro phys. 23. 147(1973). DISCUSSION HJ. HABING: Do you know of radial velocity ko of excess emission in the continuum of BD +60° measurements for the two laie-type fiants? This may 2522 at wavelengths longer than 7000 A out to prove or disprove their membership to the nebula 10000 A does not agree with similar measurements S162. by Anderson {Ap. /, 1970) nor with the near-infra red data of Allen (Monthly Notices, 1973) and Cohen R. VK>TTI: MO and MP Cas an too weak in the & Barlow {ApJ. UtL, 1973). optica! region for good spectroscopic investifations. Prof. Roatoo is nuking detailed photometric studio R. VIOTTI: The imporunl point is that there is of the oebuh. an excess of emission in the near-infrared. MJ. BARLOW: The measurement by Doroshen- OPTIC AU INFRARED AND RADIO OBSERVATIONS OF rno H il REGIONS MJ. Barlow*. M. Cohen" ind T.R. Gull**» A series of broad- and narrowband photographs nehuU and ts. shown to be due to dusi-scattEied stai- i.ï the Hi) reports NGC 763S?Sh 162 2nd ÎC 1470 light. Fiom the scalîered-hghi continuum observa aie presented. In addition to the well-known Bubble a tions and ihe variations in extinction found m both semind shell is found la be preseni in NGC 7635/Sh nebulae, a very inhomogeneous dust distribution is 162. A 5 Cltr. map showing the large-scale structure fourni- The relation of the exciting Mare to the ob of NGC 7635/Sh 162 is presented. The nebular con- served infrared emission is discussed. 1. INTRODUCTION The two H H regions that wiB be discussed in this nature of the Bubble neouU NGC 7635 (see Johnson. paper area rather contrasting pair. NGC 7635/Sh 162 1974. for further references). is a very targe, diffuse HII region, containing many This paper will be concerned mainly with the dust structural peculirities, which appears to be in a fairly content of the nebulae and its observed effects. A advanced evolutionary stage. fC 1470 (Sh IS6), on number of résolu front 1 forthcoming paper are brief' the other band, is a very young compact HII region, ly described (Barlow, Cohen A Gull, 1974, (hereafter which appears to be situated inside an extensive cloud referred to as Paper III). In Section 2, the morpho of dust and gas. The nebulae aie separated by 2° in logy of the nebulae is described; in Section 3 the the sky. results of measurements of the scattered light con These two nebulae have recently been studied at tinuum in each nebula are described, and in Section 4 radio wavelengths with high résolution by Israel, the variation of reddening across the nebulae is dis Habing A de Jong {19731 at 1.4 GHz and also ai cussed. Finally, in Section 5 the origin of the infrared infrared wavelengths by Cohen & Barlow [1973] emission from the nebulae and its relation to the exci (hereafter referred eo as Paper 1). in addition, a Urge ting stars is considered. number of papers have been published concerning the Autonomy On: re, University of Sussex. Berkeley Asirooony De pu University of Gtirarmt ' Kitr Peak National Observatory. Ml MRIOW. M (1)111 StlR lil'LI :. MORPHOLOGY Figures 1 - 5 show a series of plates taken at the radio core found by Israel. Itahtng & de Jong and has prime focus ni ilie 4-m telescope ot ilir Kin ï*cak been lounrt to have a peak valut ot Ne = 1.9 x 10* National Observatory. cm'" from the [SII| lines by Glushkuv A Karyagina Figures I and ; air both photographs of IC 14^0 119TJ| Also visible m the X 0470 A continuum plate taken through 90  bandpass interference filter, in (Fig. 2) is a second star in the south-wesl. inside the the tight of Ho + [N II) and the continuum at nebular boundaries. Il is not known if this stai is X6470À. respectively, and both show a prominent physically associated with the nebula ur is merely a tnfid-Iike structure. Whether this structure is due to foreground object. The nebula has a maximum size of the nebula consisting of a number of bright condensa .VI" north-south and east-west in (he continuum pho tions or is caused by an inhomogeneous layer of ab tograph (fig. 2). The lta + |Nlll exposu:e (Fig. I) sorbing dusi is not certain, although evidence will be shows parts of a more diffuse envelope surrounding presented in Secuohs 3 and 4 for a highly nonuniform the brighter core. This envelope can be seen more distribution of dust across the nebula. fully in the red Pakmiar sky survey print included by In both pistes the star believed to be the excita Israel et aj. and has a maximum si?« of 2'(NSIx 2.5' tion source is visible in the northern pari nf the nebu lEW,. la, on the edge of the brightest condensation. This Figuies ? and 4 show narrow band photographs condensation appears to correspond to the unresolved of NGC7635/Sh 162 in the light of Ha+(N II] and Figure 1. IC1470 centred in KKHO+mprime-focusr[2.7beam Ha.+ INII} in 90 A bandpess interference filter, 6 rmn exposure. Emulsion: 098-02. OFTïrAL. IK* RADIO OHSI KV ATKINS Of II M Kl «.IONS 25 the ctHitmunm ai A M70 A, respectively. and 4 the ihree resolved components nearest tobf> The bright Mai situated within the northern rim 60° 2522 appear m have an edge tangential to a circle of Hie Bubble is the Ol slar BD+60° 2523- In b»lh around the slar. The luperimposition <>t the three exposures the bright comet-like structure within the components leads lo the taise impression of a larger Bubble a prominent. This object has been cxien&ively co met ary-shaped object pointing away from BJ>f discussed by Johnson (Ï972, 1974], Derhaveng- 60" 2522. The best way to establish the physical Baudel 119731 and Israel. Habing&de Jong |I973] connection of these condensations to BD+60° 2522 Figures $ and 4 show that the par! nearest to BO wouid be to measure the pobnsation of the» contin 60" 2522 is noi a single structure but resolves into uum. If polarisation js measurable the direction of .three components. The brightest and most southerly the electric vector should be tangential, indicating -component has been found to have a peak value of right-angle scattering from BD* 60° 2522 We believe Ne - 1.2 x 10* cm"* and appears lo correspond to that the several bright nms and cometary features the unresolved radio component A| fo'ind by Israel outside the Bubble point towards BD+*0° 2522 moie el il On the continuum plate (Fig. 4), this „ompo- accurately than suggested by Johnson (Î974J and ncnl has a diameter of less than 3" in a Jirection this will be discussed further in Paper III radial io BD*60° 2522 The north-east rim of the Bubble is also faintly Aifuments hive been pai fotwatd by Johnson visible in the continuum plate (Fig. 4j. |l"74j and Israel et al. about whether oi not BD+ Figure 5 is a 30-min exposure between 6100 A 60° 2522 is phyiieaJiy associated with the Bubble and 7000 A showing the entité Si Î62 H ii region. A nebula NGC 7635 in general, and with the cornelary great deal of structure is apparent m the outer regions structure in particular. We point out that on Figures 3 of the nebula- In addition la a large number of bnght Figure 2. tC 1470 in the continuum el X 6470 A witka 90 h filter ord 30 imn exposure. MJ ttARl OW. tt COHFN « T R. GULL nmi the lotto winp main teaiui • viable (he star has not been a continuous process but rather has taken place in • number of phases. (i) Tlie 'innei shell- 01 Bubble ni --I.C 7635 with a Ï The high-resolution radio observations of Israel et diameter. al. fail to show structure on a scale exceeding 15'. as (lit An 'intermediate shell- with maximum dimen they have pointed out. so that the outer envelope of sions of 1' north-south am «** east-west. The Sh 162 does not show up on their map. We have northern edge ot" this intermediate shell coincides therefore mapped NGC 7635/Sh 162 at 5 GHz using with \\\t noithem edge ul the inner shell. the 85ft (2b-m> Hal Creek dish, which at that fre (in)An o «ICI envelope with maximum dimensions of quency has a half-power beam width of 11 '. Full 30' north-south and 40' easi-ivest. It ê possible details will be given in Paper HI. Our radio map is that a third mure irregular sr ! is present in the displayed in Figure 6. There is a good rorrespondence envelope, with an eastern edge almost coincident between the shape of the outer envelope in the radio with the eastern edge of the intermediate shell. map and the optical photograph (Fig. S). The maxi mum dimensions of NGC7635/Sh 162 from our ""Ve (lq73| has attempted t. explain the origin radio map (corrected for beam size effects) are 48' of the inner sheli or Bubble by ei fier a point explo north-south and 38' easl-west. A total flux at S GHz sion or continuous mass loss originating fromBDt of 13.7 + 0.6 Jy was measured for NGC 763S/Sh 162. 60° 2522. The existence of a second imermediate A S GHz flux of 2.75 • O.fi Jy was also measured for shell would appear to imply thai • he mass loss from 1C 1470. 8gure3. NOG7635/Sh 162 in Ua+(NU] with a 90 Afitter and 6 min exposure. OPflCAL !R * RADIO OBSI RVATtONS Of- It II RfcUON.S i. THE NEBULAR OPTICAL CONTÏNtlM In the A 6470 A continuum photographs of both west of BD+60° 2521 Ai (SEi corresponds to a nebulae (Figs. 2 and 4) nebular continuum emission is region 5" south and 40" east of BD+60"2522 Aj deariy visible in several places, fn an effoit to estab (NE) corresponds to the region 35" east of B0+6O° lish the nature of this continuum, we have measured 2522. Position C, is the easternmost of the three the stiength of the îif) tine and the adjacent contin components of C. Position O m IC 1470 corresponds uum a l several points in each nebula using the Wanv to the region centred 16' south and 11" east of the plei scanner on the Lick Observatory Cfossiey leflec- exciting star. Position I is centred 16" south of the 'or. The observations were made during September/ «ar and Position 2 is centred 20" west of the star. Octnber 197J. The lull details and interprelation will The position labelled 'annulus' corresponds to an an be given in toper MI but some of tJw results are listed nulus of inner diameter 10-5" and outer diameter 22" in Table 1. centred on the star. Column 1 of Table I lists the positions observed Column 2 of Table 1 Jists the diameters of the in each nebula. The names of the post'ions observed diaphragms used to observe the various positions (cir in NGC7635/Sh 162 ate the designations given by cular diaphragms were used). Column 3 gives the ob Israel et al. Aj(W) corresponds to a region centred on served continuum flux at X 4861 A. f^gôi. for each the westetn edge of the Bubble rim, 5" south and 90" position and column 4 gives the observed H3 flux. Figure*. NGC 7635fSh I62tn the continuum at X 6470. 90 kfïtier and SQ mm exposure. MJ HARLOW. M TOM MIR (UIL §H|H| k i'-'y •-mm KnsH '?>•••tezsm ;;.;• & V^H^•ff^Hl •wvi^ljUplr • ' • ••'. ^m^H HH '- ' v' '%Êi%P. *m figure J. NGC7635ISH 162. RG410 Filter: 6100 h 10 emulsion cut-off at 7000 A. F(H0) (corrected for the continuum in the places air masses as the nebulae and the reduction was based where a continuum was detected). Absolute fluxes on the absolute flux calibration for a Lyrae given by were obtained by observing standard stars at the same Oke & Schild 119701- Column 5 of Table 1 gives OPTICAL. IK A KADIO OBSERVATIONS OF II II REGIONS Table I Diaphragm '4W.I Kilion F NGC7635/S1| 16: Ai 2; HU* 1 1 22.7 * o.5 = A,(W> 29 1.4 + 0 4 4.4 + 0.1 320 *'3 70 Aj(Sli) 2'> ft.2 + 1.0 11.3*0.2 ITO » 30 A.INtl 22 3.4 + o.a 6.7 + 0.2 »*s 11 2: .v: » 0.: >220 r, 22 4.5 + 0.3 >310 r, :2 6 2 + 0.2 >430 c, . 22 3 <> * 0.2 >270 K 1470 0 22 1 5 + 0.5 4,6 + 0.2 "'i'^ 22 4.4 + 0.7 26.2 + C> ' -:;20 22 1.3* 0.5 1.4+0..' • W(I(|J). the ratio of F(Hp") to f4g6). which is a mea shaped obscuring patch. sure of the bile out of the continuum (in A) required The expected aioirtic contribution to the contin lo give the same flux as the HP l'ne- uum at X 4861 A can be calculated from the tables of Inspeclion of Table 1 shows that a continuum Brown & Mathews ( 1970J - For an electron tempera- was detected at all points observed in IC 1470 and in lute of Te = 10* K *nd election density (in the hjrtfi) (he components A| and Aj of NCC 7635 (but not in of zero, W(H0> has a value of - 1300 A. Increasing ihe bright rims fl. C,. C2. and Cj in the density increases W(H0) as does de..™-sing the NGC76J5/Sh 162: these componenls are not visible temperature. Since the observed values of W(H0) aie in the continuum phoiograph (Fig. 4) whereas both very much smaller than 1300 A, one must therefore A| and A2 are visible). The two separate measure rule out atomic processes as being responsible for the ments of W(H0) for component A, in NGC 7635 observed continuum. The origin of the continuum show good agreement as do the measurements for must therefore be light ftom the exciting stais which Aj(SE) and Aj(NE). The strength of the continuum has been scattered by dust particles in the nebulae. in IC 1470 is found to vary strongly with direction Similar strong scattered light continua have been and dislance from the exciting star. The strongest found in several other HI] regions by O'Dell A •relative continuum is found al position 2, which cor Hubbard {1965] and O'Dcl!, Hubbard & Peimbefl responds lo the western edge of the apparent Y- [1966]. Ml HARLO*. M. COUINA I.R WU. 4 REDDENING VARIATIONS IN THE NEBULAE Comparison of the lip fluxes listed m Tante l with the 1.41ÏH/ fluxes measured h> Israel el al.for the same components enables one to derive the total cMincuon at HjS for a number of different repions m NGC ~t>35,'Sh 162. Table ^ lists the appropitalc quantities. Column I pn.es rhe name ot the compo nent, column 2 its nominal radio sue as given by Israel et al.. Column .* gives ihe 1415 MHz radio flux of each component, column 4 gives the diameter of the diaphragm used in observing the component and column ? gives the reddening constant C^g ^A log llH^I. The quantity was derived from the observed radio and H3 fluxes using the formula of Higgs 11073). with Tc = 10* K. Finally, a value of E|B-V'l coriesponding to the derived value of C^o ..an be obtained by assuming an appropriate redde ning law In this case the Van de HulslCuive No-IS (Johnson. J9681 corresponding to R = 3 and E(B ~V) = 0."2 Cf|£ has been used (see below). Inspection of Table 2 reveals thai there is a signi m ficant variation in extinction from component to 21 20 17 23*16™ component in NGC 7635/Sh 162. Since the nominal radio sue ot each component is less than the dia phragm diameter used for the H0 flux measurements S GHz map of NGC 76SS/Sh 162 Tele il is possible that the H3 flux is overestimated and the scope half-power beam width = //'. Con reddening therefore underestimated. tour units (we 0.01 ft in steps of 0.05 K. The cross marks the position of A spectrum which has been taken crossing the BI>+6 Tabk 2, Variation of Reddening NGC 76J5/Sh 162 Radio size S]4I5 Diaphragm Component L E(B-V) (arcs) (Jy) (arc s) H& *l 12 0.75 29 1.9 B <9 0.07 22 1.8 C, <9 0.28 22 2.2 c, <9 0.28 22 2.1 c, <9 0.28 22 2.3 (MTK AI. IK A RADIO OBSJ-RVATIONS Of H H RftilUNS 31 |l V DI 1)41 which (oi an awumcd IB V|„ For IC 1470 an estimate of C|(g for the radio (U2 leads h> HB V), = 0 7.1. component (core) A can be obtained trom the l|£ Tlic extinction implied by ihe optical measure fluxes (corrected for the stellar continuum) mejsuie-1 ments alone is (herefore s^nilkindv less than the with 10 5" and 22" apcituies unit ltd on the Mar cutmction derived by combining the optical and tadio .Since the diameter of ihc radio component A is < ohservalions. 1 5". we ubiiin the limits * 2 <* ("m < 2.6 which give A severely abnormal irddcning law in the duet- 1.6 < HB V) < 1.'» from a spectrum ..I ihe nehii- Hun of MIC 7635 can be ruled «nit by itie mlrarcd la nf-iaincd with in Hi" aperture a value ot KiHa dala available lui Bl>+ 60° 25:2 Inspection 'if H01 = 14 has been derived which gives L(B V)neh f-ipure I ol l'apci | shows that out to 3.6 urn the llux = I 2 Tlie UBV photometry ol the exciting star he distribution i>l this stai corresponds m the Rayltigh- Kostjakova ct aJ. f 196K| leads to a value ol Jeans tail ni a black body. K. the ratio ot total to HB V), = 1.2. 3n< scleclive absorption, is close to by L'^B V * Persson & Piogel |1 5. THE INFRARED EMISSION AND THE EXCITING STARS Tabic 3 displays some of the derived parameters discussion of the energetics of this nebula must awaii for the two nebulae. Column 1 gives the nebula name, infrared observations at longer wavelengths, where column 2 its kinematic distance [see Paper I| and any cooler dust present might be expected to show column 3 gives the nebular Lyman-a luminosity, up. Lfv-a.; derived using Ihe formula of Rubin ( 196S) for We have suggested in Paper I lhat the infrared the total number of ionising photons emitted per emission observed to be concentrated round the second multiplied by the energy of a Lyman-a pho 0 6.51Uf star BDtf30° 2522 originates from dust par ton. An electron tempeiature of 10* K was assumed. ticles condensing the stellar wind (this phenomenon For IC 1470 the 1.4 GHz flux measurement of Israel has also been suggested for the central stars of certain et a), was used and for NGC 7635/Sh 162 our flux planetary nebulae (Cohen &, Barlow, 1974]. tond &. measurement quoted in Section 2 was used. Frost [1971] and Walborn H973| have recently Column 4 gives the nebular infrared luminosity, L]R, found BEH 60° 2522 to have spectral peculiarities, calculated as described in Paper I and Column S gives with double-peaked emission at the HellX 4686 line, llic ratio of LJR to L^y-a- implying a large rotational velocity. Conti & Frost It can be seen Sat for NGC 7635/Sh 162 the [1973] have reclassified it as ad Oef star, and it available Lyman-a photons can adequately account appears to have similarities to the Be stirs, objects for for Ihe infrared luminosity out to 20 fim. Any further which ciicumsteUar dust formation has also been sug- Ml BARIO». M COHI-N * TR «I'LL Table 3. Infrared Parameters 'JK Nchub „ M M (fcpcl 'Lei (LQI U.v"<, < 0> < 0> WHIh 1C1470 4.3 l.Sx I04 1.6» 10 2.HxlO"* 2.8 (core) ID"1 34.6 (total) 8x Iff* NGC 7635 3.5 6.1 x l(J* 5.7 x 10* gesied | Allen & Pension. 1°73|. Note thai the deriva in the nebula (see Fig. 2) has sometimes been des tion by Israel et al. of a distance of 3.5 kpc for BD+ cribed as liming a spectral type of 07 (e.g. Glushkov 60° 2522 using V = 8.67. E68] and Chopinet et al. [19731 lead to a distance of 2.5 kpc. The kinematical dis yield an absolute visual magnitude My of between tance of 3.5 kpc for NGC 7635/Sh 162 implies that -4.2 and -4.6, for R = 3. implying that it must he a Mv = -6.2 for BD*60° 2S22. main-sequence star. Column 6 of Table 3 gives the mass of dust in If the AFCRLfluxes given in Paper I are used lo IC 1470 required to provide the observed infrared derive an infrared luminosity, a ratio of infrared lumi luminosity, calculated in the same manner as in nosity (out to 20Mm) lo Lyman-a luminosity equal Cohen & Barlow [1974]. Column 7 gives the mass of ling 10.5 is obtained. This number is larger than the ionised hydrogen derived by Israel et al., adjusted for ratio of total stellar luminosity to Lyman-a lumino the slightly different distance assumed here and sity for stars earlier than 09, according to the tables column 8 gives the dust-to-gas mass ratio. Even if all of Panagia [1973J. and if correct would imply lhal the emitting dust were in the radio core no excessive either non-ionising infrared components ate present ratio is found. or thai ionising photons are being directly abs. .bed For IC 1470 the excitation parameter U is equal by dust inside the H 11 region. It would therefore to 49 pc/cm1 for a distance of 4.3 kpc. From the seem important to map IC.1470 at 10 and 20 pm in table of Panagia [1973], this implies a spectral type order to see if the AFCRL fluxes are confirmed. of earlier than 08 for the exciting star. The bright star «.ACKNOWLEDGEMENTS We would like to express our thanks to Di. Carl observations. We would also like lo thank Dr. H.M. Heiles for his help in enabling us to obtain the radio Johnson for discussions. 1. Barlow, M J., Cohen, M. & Gull, T.R., in prepara 5. Cohen, M. A Barlow, M.J., Astrophys. J. Lett, tion, 1974 (Paper III). 185 U7< 1973) (Paper I). 2. Brocklehurst, M-, Monthly Not. Roy. Astron. 6. Cond, P.S. & Frost, S., BAASS, 402 (197?). Soc 153471(1971). 7. Derharving-Baudel, L, Ment Soc. R. Sci. Liege. 3. Brown, R.L. & Mathews. Vt.ii., Asuophyi. J., Ser. 6. 5, 357 (1973). 160,939(1970). B.Glushkov, Yu.I. & Kiiyagjna. Z.V., Astron. 4. Chopinet, M.. Georgelin, Y.M. St Lorui-Zucker- Tsirk, No. 711,4(1972). mami, M.C.. Astron. end Astrophys. 29,225. 9. ffiggs, LA-, Monthly Not. Roy, Astron. Soc. Omt AL IR II RADIO OH5t-.RVATIO.NS OF ft II Rf-GlONS 33 161,513(19731. Springer Verlag. New York. 1968. 10. fckc. V„ Astmn. and Asimphys.. 26. 45 (1973). 16. O'Dell, C.R. & Hubbard. W.B.. Astntphyi. J., 11. Israel. F.P.. Ilabmg. H.J. & de JonR. T.. Altran, 142,591 (1965). and Asirnphys., 27,143 1t'>73). 17. O'Dell C.R.. Hubbard. W.B- & Peimhert. M. 12. Johnson. ML, in 'Nebulae and Interstellar Mat Asirophys. J. 143. 743 ( 1966». ter'. Eds. R.M. Middchurst and LU. Aller. Uncv. 18. Oke. J.B. & Schild. R.fc.. A*tn,phyi. /. 161. i.f Chicago Press. I96K. 1015(1070). 13. Johnson. MM. Mem. *«•. R. Sa. l-icge. Ser. 6. 19. Panagia, N.. Aitron. J., 78.929 Ï19731 3.345(197:). 20. Persson, S.E. & Frogel. J A.. Astmphyi. J.. 188. H.Johnson. H.M., Ai/mit. and Astmphys., 32. I" 523(1974). 11174). 21. Rubin. R.II...4H/opAvs./. 154. 391(1968). 15. KostjaVova, E.B. Sa*e1eva. M.V.. Dokuch- 22. Walbom. S.R..Astrttn. J..7K, 1067(1973). aeva. C.I). & Noskova. R.I.. IAU Symposium 34. DISCUSSION II. J. HABING. Is your explanation of the diffe fc.E BECKL1N When you quoted the 20Aim to rence between Eu,.y from Htz/H£ and fc[j.v from Lya ratio for IC 1470. did you use your own mea 21 cm/H# based on die presence of internal dust in surement or an AFCRL measurement'' If it is an the nebula, as discussed by Mathis-1 AFCRL number I would like to point oui that details of how these numbers were obtained have not been M.J. BARLOW: Yes. published and it may be scientifically unsound to use such numbers in a published paper. J. MAYO GREENBERC: On the basis of ihc total extinction as you derive it. have you made an .MJ. BARLOW: The AFCRL measurements were estimate of the dust to gas iatios in these regions? used for the total infrared luminosity estimate. This estimate is used merely to suggest that it might be M.J. BARLOW: In the case of NCC 7635 the worthwhile to map this object ai 20 pm from the mass of dust is insignificant because the luminosity is ground. low. For IC 1470. if you assume all the dust is in the 30" core the ratio of dust to gas is 10"3 and if it is L. HOUZIAUX: What theoretical ratio did you within (he total 2' nebula the ratio is Iff4. This as assume for the Ha/HD intensity ratio? If the density sumes an emissiviiy of 2iraM for the dust emission. is higli enough (> 10*cm"3), an optically thin core may not be the most appropriate one. R. VIOTTI: Have you made an estimate of the mass in NGC 7635, especially of the shell and of (he condensation neat this star? This would be important M.J. BARLOW: Brocklehursfs [1971] theoreti in connection with the problem of mass loss from the cal ratio (for Te - 10* K) of 2.85 for the Ha/H0 0 star, in particular if they were really ejected from intensity ratio was assumed. (he star. The spectroscope studies of Deharveng-Baude! 11973 f and Glushkov & Karyagma {19721 show that MJ. BARLOW: Mass estimates for the various in both nebulae the maximum electron densities are components of NGC7635/5h 162 have been made by <2xlO*cm"J. Israel. HabingAde Jong(1973]. 1.2. Infrared Observations COMPACT INFRARED SOURCES ASSOCIATE» WITH SOUTHERN H 11 REGIONS Jay A. Fiogel & S. Eric Perawit Center for Astrophysics. Harvard College Observatory and Smith-itmian Astrophysics! Observatory,Cambridge. Ma».. USA ABSTRACT We Itjvc inunit bridu. compact, mfrared lengths do not vary ugnificamly with position, imply ( I-25/im) sources associated with eleven galactic H II ing thai the Jusi which radiates m the 10-20pm legions. We will present maps showing complex struc legion is well mixed with the ionised gas. Also, we ture at lO^m in live of these sources. The remaining find lor I his dust a tower limit to ihe ratio M(H 11)/ ones are characterised by a small (<20") cote of high M(du*l>. which, for a reasonable choice of physical surface l-ngluness. with an extended RECENT OBSERVATIONAL RESULTS 1. Mure detailed observations of the silicate absorp infrared source whose energy distribution re tion feature at 9.8jim confirm the correlation of sembles those presented in this paper. There is no silicate and formaldehyde absorption toward the evidence for silicate absorption, but we do sec ice sources studied previously. Also, no sources absorption ( I mag) at 3.1 (im. shows the silicate feature in emission. 3. NGC 3603: The region surrounding this very 2. OH284.2-0.8: This peculiar OH source is a bright young cluster was mapped at lO^un. The emis- 3u s \ IR stun ts close 1) c-twclaied with the Ita emission, s Hi W |2J! Ex I ended 10pm emission was found which lorms an arc around the cluster The dusl at a position corresponding to the radio peak. [articles emitting lhe in Ira red must he as old as Tins source resembles those discussed tn the 1hfi.lt1Mer.vi/. > 10" >cns papci- 4 G.i".°-0 > The region neat this radio •Miurce u.n mapped jnd shou> two distinct peaks of emission al 10 and 'Opm There are significant variations This paper will he published m the Asm>physu-at in the 10pm 20pm colour température Hum one JiUintalm I'm. part ni the nh)ect TO the other DISCUSSION t BUSSOU Ft I How do you calculate the inte I MAYO GREENBERC. You say thai Ihe dust grated IR fiuxeitrom your sources toobtain the lumi lo ga> ratios yuu get arc lower than tn the nurmal nosities" \\ «huh wavelength dn you fix the maxi interstellar medium Whal si/e of particles is this mum IR emission and how do >ou fix tlirs value'' based on-1 L:se of the Whjtford curve for example implies a certain st?e distribution fut the particles. :> E PERSSON l'lie luminosities refer onh to Particularly the values of Av you derive should he :lie 1 - 2Spm range. If the infrared energy distribu strongly si/e dependent. tions in the far infrared resemble those of other IIII regions, (hen the total luminosities are larger than the J.A. FROGEL: The Whit ford curve didnot enter 1 - -5 pm luminosities by a factor of 4 or 5. into the estimates of the dust masses which were determined from the emission and assumed a particle E.E. BECK LIN: I would just like to comment size or 0.1 wm. We thought the most reasonable thing thai it is only meaningful to compare the 1 -20um to do in the case of the extinction was to take a flux with the radio flux in cases where you have high standard Whit ford law as we have no idea what the resolution radio maps so that you know what you arc dust which is doing the absorbing is like. looking ai. For the distant sources you arc probably integrating over a number of objects in your beam. D.K. AITKEN: With regard to your comment thai you only see the silicate feature in absorption: in A.F.M. MOORWOOU Firstly, do your dust to bnth Ihe Ney-Allen source in Orion and in r/Car the gas ratios apply to the central regions of these sources 10 pm silicate feature is seen in emission. I would like only, and secondly, how many of the sources ob to ask how you estimated r( •.? and whether or not served appear to suffer local extinction? you made allowance for a possible emission feature (from the underlying source) at this wavelength? Al J.A. FROG EL: The dust to gas ratios apply to the so can you say what the relation is between the opti individual infrared components in each region. We cal depth at 11.7 pm and nearer the maximum of the have used the observed FWHP sizes. It is difficult to 10 pm absorption feature? separate the local extinction from the instersiellar component but a third to a half of the sources have J.A. FROGEL: We estimated r,,., by taking the values of Av thai are not inconsistent with interstellar continuum as defined by the measurement at 8.7 pm rather than local extinction. and 12.6 pm. No allowance was made for possible emission features. In answer to your second question, One important thing I should say with regard lo ri i .-7 pm ;.c?les with r».» pm. the 10pm silicate feature is that in none of the cases do we see emission. There are four or five cases where L. HOUZIAUX: When extrapolating the fluxes the spectrum is almost flat and in all the other cases due to free-free radiation of your sources to shorter there is absorption in varying amounts. This indicates wavelengths, is this flux compatible with what is ob that the silicate panicles responsible for the absorp served in the visible? I would also like to make (he tion are not the particles which are giving the emis comment that I think you could get more reliable Av sion at 10pm. value; by using fluxes in the infrared and shorter (UMI'ACT IK SOI RMS VSSO('IAiH> wifH SOI TlfUiS H II KH.IOSS wavelenjrt!i*. The observed waller in Av might then riot he caused h> différentes in the iump-ismon .>t he reduced the dust It can instead he caused by (he dumpiness ot i he dust across the fj,.c ut tlie source lor example J A IKCKilL There arc no visible observations consider a cloud with a small hole, iheri fcfi.j^ may lor must of the sources but the results are not incom indicate no absorption while Tsilicate a higli one patible with the lack i>l visibility. With regard n> your second point. Hie values of Av are based just im the JA PRfK^hL fh's is certainly a possibility, l.o • 2.2 pm colour. however there is no dumpiness un a scale comparable to our measuring aperture, since uie infrared colours arc sensibly n.«slant over the objets we have obser MV I'hNSTON A lack U corrélation ol fc„.K and ^silicate observed from extended soun.es need ved 39 INFRARED OBSERVATION OF NGC 6334 E.E. Becklin & C. Neugebauer Hale Observatories, Cilifomi» Institute of Technotojy. Carnegie Institution of Washington, USA ABSTRACT Infrared photometric observations of three com component of the infrared emitting region is less than ponents in NGC 6334 have been made. Two of the — I* in diameter at 10 fim and shows a strong 'sili components arc associated with compact H II regions cate' dust absorption featute. In many respects this and are similar to the sources in W3. The third com source is very similar to the 'BN' infrared source in ponent is almost coincident with the OH maser sour the Orion Nebula. ce and shows no known radio continuum emission. A I. INTRODUCTION NGC 6334 is a complex of sources showing, be CO [Wilson, Dickel & Dickel, private communication; side» optical nebulosity, far infrared (Emerson, Jen Kwan and Solomon, private communication] and nings & Moorwood, 1973), radio continuum (see, for HCN emission [Zuckermann, private communi example, Schiaml & Metgei, 1969), OH (see, for cation). In this paper, we present infrared observa example, Raimond & Eliasson. 1969], HjO [John tions between 1.6 and 20 pm of selected areas of ston, Sloanaker & Bologna, 1973; Sullivan, 1973], NGC 6334. 2. OBSERVATIONS Both photometric and mapping observations were sonetaL(1972). made at the 1 -m telescope at Las Campanas Chile and Scans at 2.2 and 10pm with 30" diaphragms were ihe 200-ii.eh Hale telescope at Palomar Mountain made covering the area of the OH emission source with conventional infrared photometers. Measure and of the HII regions G 351.34+0.6 and ments were made at 1.55 um (AX = 0.3 um), 2.2pm G 35I.31+0.6; these areas correspond to the peaks in (AA = 0.4um), 3.Sum(AX = 0.6 urn), 4.8 urn (AX = the 40- to 350-Mm maps of Emerson et al. [1973], 0.6pm), 8.7pm (AX = 1.2pm). 10.1 pm (AX = Photometry and maps with a 0.5" x 3" slit or a circu Spm). 11.2pm (AX = 1.5pm), 12.5 pm (AX = lar aperture 5" in diameter were also made of the area 1.3 fim) rnd 20 pm (AX = 7 pm); diaphragms for pho- surrounding the northern OH emission centre tomcl'y were either 5 or 30" in diameter. The calibra NGC 6334 A. tions of the photometry have been described by Wil- I t HH'KLIN J C, NI ICI It AI I K y RESULTS Maps oï the jica aJjjcfnl in the northern ceniic The «mice is ihus 0.4 s east and 8" north of the of OH emission are shown in F-igmes I and : Struc average position of the lWi5-MH? Oil emission, as ture is seen at 1 2 /int covering an area about l' de 1er mined by Raimond & FJiassrtn|IWl|, it coin squa:e. although the brightest source contains a cote. cides, however, within the «iron, with the position of NGC ô334 (RM |. which is unresolved with a ?" aper one of the velocity components of OH emission. ture At 111 and JOjim, vans show*J only this Mngle Scans at 20 urn with a 7" x JO" slit showed no other component, slit scans with l" resolution sliuw thai sources in ihe area • I -in right ascension by •* Z.in more than 41K of the lOfmi tadunon coniesliom a dechnaliun atound NGCi>334/IRS 1 sit nngtf than region less than 1~ in diaineier. The co-oidmaics of - 1 5 the flux level of 1RS I. Scans at 10urn at the NGC0334 1RS I aie(l«50.0| I- ..ration of the southern OH source NGC (.334 OH/B h m s a = |7h|7m.?;..ss + 0.4* lttSO) - 17 16 36.3 . AII1S0» = 35° 54' 57". timond & Kliassonll'Xi^Qshow no source grcatei than -:50l.u. llie energy distributions of NGC JJ4i (^\ N&C65J4i :0«. A map of the area of NGC 6334 OH/A -\ made by taking scans at 2.2 fim on the 200-inch telescope. Tlie resolution a shown at the upper left corner. Contour intervals are separated by ~gjr 10~70 W #: m~* /ft:"1 sfl. The three solid crosses indicate the position of the 1665-MHz OH emission in the ranges -11.9 to <0M M. * - I3.0 km/s (north), -?.0to -I3.0km/s f , (middle) and -8.5 to -9.5km/s (south/ fRaimond é. Eliasson, 1969/; lite dashed cross indicates the position of the HO t Same as Figure 1. but fc 10 tun (left) source /Sullivan, 1973}. All co-ordinates and 20fim (right): contour intervals are are 1950.0. Vie cross-hatched area at left ,s 7 1 1 l.5xI0~ W ni Hz v" flOfim} is a visible star. 15 7 1 and 0.8 x Iff Wm' Hi'' if (20 urn). IM-RAKI-.Il OBSERVATIONS OI- fitiC fi374 4. DISCUSSION The most sinking feature of the data is the simi silicate absorption. Both are located near, but not larity between NGC 6334/IRS 1 and ilie so-called coincident with. OH sources and both have a central 'UN' source m Orion (Bccklin, Neugcbauer & unresolved source surrounded by 3 low extended Wynn-Williains, l°7.î] As wen in ligure 3. both background. If, following Schraml & Merger \l')(>')\, sources have similar continua, and both show strung Ihe distance io NGC 6334 is taken to be 0.6 kpc. (he 1 - 20 urn luminosity of NGC 6334/fRS I is - 300 If.) while that of the BN source is 1500 lG In both cases, this is - )"' uf the total infrared luminos ity [l-.mcrson et al.. 1973; Harper. I974J. The strik ing difference between (he depth of the silicate fea ture in SGC (>334/l"S 1 and that in the adjoining il II regions is equally noiewnrthy. It thus seems m this case, JS is generally Irue. thai strong silicate tea- lures are seen in the more compact infrared sources. while they are cjuiie often absent in the infrared emis sion from the more extended sources. Figure 3. Vie energy distributions of \OC 6334/tRS I with SO" diameter and 5" diameter are shown as well as those of the HIS renions G 351.31*06 and G 35i 3^* 06 G 351.34+0. ft with 30" diameter aper 0 35131 -06 tures: the latter is plotted J factor of 10 NGC6334/IRS i 30 NGC 6334/IRS l Ï below Us actual mlue. Errors are of the order of ± 15% unless explicitly shown. The energy distribution of the BN source in Orion with a 5" diameter aperture is also shown, but plotted too bright by a ^13 0 i3? '3» 136 «a i factor of lOfBccklin et at. 1973f. log («equency 1. Beclclin, E.E., Neugebauer, C. & Wynn-Williams, 817(1969). CG., Astrophys. J. (Lett.) 182, L7 (1973). Schrami, J. & Mezger, P.G. Astrophys. J. 119, 2. Emerson, J.P., Jennings, R.E. & Moorwood, 334(1969). A.F.M., Astrophys. J. 184,401 (1973). Sullivan, W.T., Astrophys. J. (Suppl. # 222) 25, 3. Harper, D.A-, Preprint, 1974. 393(1973). 4. Johnston, KJ., Sloanaker, R.M. & Bologna, J.M., Wilson, W.J., Schwartz, ' P.R., Neugebauer, G., Astrophys. J. 182,67(1973). Harvey, P.M. A. Becklin, E.E., Astrophys. J. 177, 5. Raimond, E. & Eliasson, B., Astrophys. J. 155. 523 < 1972). J. BORGMAN: The statement that the 10/im not true for the galactic centre. This comment is rele- absorptiun feature is found only in small structures is vant in the context of your paper if we adopt the > 42 I I Htt'kUS A <- MK.tHAl I K ne» thai Sgr A Wesl lu> j I lioim.il spectrum and lurc ot ||ic "silicate" absorption feature wen m llic coincide* with the extended >nuice ol Id ami .'' mi galactic ceiilrc may well he quite different from Ihs radiation. feature »ccn in compact iources associated wiih || [[ tc^mns For example, most of the extinction to lite E.E. BECK UN: I agree ihai the 10/im source* in galactic centre » probably interstellar, while the ab Sgr A Wesl piohabK ate thermal. However, the na- sorption m the compact source s IS cireumnehular. 43 RECENT OBSERVATIONS OF THE H -13 urn SPECTRA OF H II REGIONS D.K. Ailken. B. Jones & J. Penman Department of Physics and Astronomy. University College London. UK ABSTRACT The H • 1.1 fini speclra ul a number nf compactt independent of (he particular source. IIII legions are coiisisicnt with a simple model of a) Ionised neon has been detected m the galactic wan» source surrounded by a cold envelope of <>bs- centre source Sgr A (West), confirming the thermal Lining my I trial. The same absorption curve applies toi nature of this source: the neon abundance appears in the cmilting and absorbing matter and appears to be• be normal. I. NTRODUCnON We arc reporting spcciral observations of some longer integrations. Wavelength calibration is by refe 11II regions in ihe I Ofim atmospheric window, using rence to sky emission features of COj, H20 and 03 the TNT. Radcliffe and Tenerife telescopes and the and is good to better than + 0.01 jim. Other details of UCI- grating spectrometer. Observations can be made the observational techniques have been summarised in at two resolutions A\/X = 0.005 and 0.015 and small Aitken&Jones|l973a]. legions around emission lines can be selected for 2. CONTINUUM SPECTRA OF SOME H II REGIONS BETWEEN 8 - 13um We have found that the infrared spectra of many is assumed to be the same, and to allow for extinction H II regions arc well represented by a simple model at 8 pm an optical depth of 1.5 is added. The fits do consisting of warm dust in emission seen Ihrough a not depend strongly on the precise value adopted for cold dust envelope and that the same absorption this 3dditive constant; the resultant curve is very simi curve fits all the observations U> dale. lar to tnat derived from the infrared emission source The source IRS-5 in W3 |Aitken & Jones. 1973b) in the trapezium region of Orion measured by Gillett still has the deepest silicate absorption feature known & Stein (Woolf, 1972], and also some of the circurn- In us. We use an absorption curve derived from it, stellar excesses. Laboratory spectra indicate very little since it will be least affected by the form of the absorption from silicates at 8/im and the value re underlying spectrum. The details of the procedure quired must reflect absorption due to other compo have been described elsewhere jAitken & Jones, nents of interstellar matter. The optical depth to 1973a). but essentially the underlying spectrum is IRS-5 al i0.4jjm is -4.0 (relative to 8/im) which, taken os a black body, the extinction at Sand I3ftm using Gaustad's [1963] value for a typical silicate PK A11KIN. B JOMS A i P1SMAN prrv • ~:TN S I f-'ifurt-i 1 Observations of an J model fits to Sgr A and 2 (Westjand the B.\ object. Solid line sttows best fit tu an optically thin source, dashed line is best fit to an optically thick soune. "Pie BS data are taken front GillettA Forrest {1973}. (enstatite), leads to an amount 1.2 x Iff^g/cm' of this material in the line of sight. Using this absorption curve for an optically thin or optically thick source seen through a cold obscur ing doud of the same material, best fits have been computed for a number of sources. Figures 1 and 2 show these for the infrared source in the galactic centre and for CJletl & Forrest's |I973J data on the Becklin - Neugebauer (BNJ object. In both cases the best fit results from an optically thin source. Gîlletl & Forrest also report spectra of the Kleinman - Low (KL) nebula which indicate a much larger extinction to this abject than to BN. These measurements were made before detailed maps of the complex of sources in this region were available (Rieke& Low, 1973a]. Separation of KL from BN was from the difference between two spectra taken with different beam sizes and the indication of very large extinction is due to a relatively small difference in the observed fluxes near 8^m. We have made new observations of KL, in which separalion of KL from BN was achieved using Spectrum of and model Jit to the KL ne bula. RM-fWI (JBSIKVAIIOSSOI K IJ *im SPMTHA OI II II Hi MOSS an II" beam with IS* throw in RA The %pttirum is «.&£ 'S 1 IKi'KI •.Itown in figure .1 and is well represented hy jn opti cally iiitck source of IJff'K suffenn$ only jppfoxj- mately the umc extinction as BN The cluster <>t un resolved sources in the same field as Kl. may conm- l>utc slightly at H • '' Aim but due to their much higher colour temperaiure will nut significantl> aflect iite Ifinji-waveiengEh points. Photometry of these sources suggests that they may suffer greater extinc V tion than either BN or KL. and it t» natural tu ton- siiler them as source* embedded in the optically thick Kl nebula with HN itself as an outer member of the pioup The whole tumplex then is obscured h-. colder dust. \ / : Figure 4 shows the H\3fim specfum of NGC" 75-18. The absorption feature here i\ very deep and it « not possible to distinguish between the cases of an optically I hick or thin source. Predominantly the spectrum is from 1RS - i, tut in our 15" beam there will be some contamination from 1RS - 2. Data on K3 • 50 and W5 ! due to Gtîlcit jpnvaïe communication! and on the AFCRL source «09-2992 (Munit & Soifer Î974J are also weii fit- ted by the same model. Spcfirum of and model fits Jï M,T 7538. Solid and doilicd linn are S m Figures I and 2. Table I. Absorption ta tome H SI regions Optical depth relative to JRS-5 Estimated A» Soutte (SgjA) = 30m optically thin optically thick A (BN) « 70 m Av cenlral source central souice mag mag IRS-SinWJ 1.00 116 42 Sgr A (West 1 071 82 30 BN 0.60 70 25 KL 0.60 70 25 HOC 7538 0.84 0.53 97/62 35/22 G333.6-0.2 0.31 36 13 KJ-50 0.4S 52 19 W5I 0.40 0.15 46/17 17/6 AFCRL «09-2112 0.40 .13 17 PK AITKI N. H ICWISa ) nSMAS Table 1 compares the silicate extinction feature in the extrapolated radio tree free II us winch is equiva a numhei .»t" H 11 reports In none ot these is the lent to ,\ ^ 1^ map IBecklinel al.. I«l7.l|. The ratio visual extinction known unambiguous!*, hut various \ A|„ « - 7 lor both the galactic centre and arcumcnls haw hecn used in estimate this quantity (i.l.Vl Ml ;. tin! taking Av - 70 mag loi the HN oh- lot a number pi souices It the HN oh|ect is a hcavils jeu the lain- is consideiahlx highci. al AV'A|„.» " leddened F supcrpant. n ntu\t have a visual extinc 20 Ptt'hahVj the ntosi suspect ol the estimates of Av tion Av "r "Onus Mansion. Allen & Itvland. 1*»"I|. is based on consideunp BN as an I supciftiant. and the - ' ym source at tile galactic lomie has .\ - although Av/A|„.» may turn oin m vais locally, the 30 mac by comparison with the nucleus ni M.' 1 ] Beck- evidence at present favours a value of about 7 for this lin &. Neugchauer. 1<«IS| and the Mil tccion i; .> >.! t> • 0 ' has a deficit at 2 2 pin compared with .V Ne U UNE EMISSION FROM H II REGIONS Pu- Jcterminaiion ot the abundance ot neon pnncipte oltcrs a reliable method ol c^iuiuiiiig this irom opika] observation ot cjrh t>pe stats and dit- abundance lot a number of teasons. The I ' XOum luse nebulae is Mibjet.t to a number i>t uncertain lu--- hue jrises tioui fine shuituic splillitip ol the ptound and the disc icpanc tes in the tesulls trom these ohsct- state of Ne 11 and Us intensity is onl> very weakly uuuns are only, no* hemp icsulved Measuiemenis ol lempcraluie-depcndenl. at election densities envi- ihe intensity ot the Ne II intiared line at 12.KUpm in saped m compacl H 11 regions, it is also almost indc- Table 2. Ac // lineemissum tn hXtltWli»!! Observed Htam optical C'uiKclcal î aii Assumed S*MIKI: ïlu* dramcler ueplh flus. ladw flu* et'tective Neon 10" art s al Wuri'MO'- f.u. radio Oux abundance Soles 12.8 Jim in IK beam 12 • 1,-s SV/Np G3336-0.2 314 13 0.47 500 K5 85 7.36 7,<>3 K3-50A <:5 16 0.68 <50 1.5 1.5 <8.10 K3-50 f <10 068 <20 3.4 3.4 <7.31 1 1.3 <7.76 2 W3 [RS-3 <:3 16 1.5 < 100 8-10 - 5 <7.87 3 DR-2HN- -I. . _ <30 16 -1.0' <80 5 5 <7.78 4 IC418 Sgr A CUesl 1 95 t 22 25 1.05 270 + 60 25 25 7.60 12 7.93 6 S.23 1. Assuming same extinction as Tor K3-50A. 2. High-resolution measurements show ullracompacl sources containing ~ 1.3 f.u. (5. Harris, privale communication). 3. Assuming same extinction as lu 1RS-5 in W3. 4. Estimates of Av ~ 50 m for this source by C.G. Wynn-Williams, F..K. Beeklin & G. Nuugebauei, Ailrophys. J. 187.473(1974). Kl-CI NT aliSI KVATÏONS Of 8 • 13 f/m SPKTRA 01- II II RKJIONS pcndciil il electron density. The atomic parameters, mic-ray observation*, was arrived at hy assuming thai in llus case the collision sircngth. are well determined the radio tlux of «5 f.u. |Shaver & Goss. i'n()\ was ami in Ilii' radiation field associated with f) stars near spatially distributed in the same way as the infrared ly J]1 the neon should be singly ionised. Iitially, even continuum flux, giving between l? and % of the in heavily obscured IIII regions the line does not radio Jlux within our 13" beam. suffer very serious attenuation, jnd the latter can We have looked for the Ne II line in a number ol tit11-n he estimated using the methods of the prc.jous It II regions known to be highly compact at radio section. The determination is made relative to the frequencies. Wilh one exception, we have not detec hydrogen abundance from radio observations at fre ted the tjne from these objects. The results are sum quencies lu pli enough lo ensure an optically thin marised in Table 2, and it appears that the main rea source. son for the non-detection must be atinbuled to ex The neon abundance derived fmm ihc measured tinction at 12.8 jtm which vanes between factors of 2 neon line intensity in G333.6-0.2 [Aitken & Jones. to 5 for the sources considered- The upper limit is 1974| is uncertain mainly because of the insufficient consistent but very close to the presently accepted spatial resolution (4') of the radio observations. The value of 7.9 for the log Ne abundance. At a later date value 12 + logNe/Np between 7.63-7.93, in agree we hope to extend the integration times on these and ment with optical observations of Orion and with cos other objects. 4. DETECTION OF Ne II IN Sp A (WEST) The radio source at the centre of the galaxy has At 5 GHz, the flux from Sgr A (West) is ^ 25 f.u. been the subject of considerable speculation. Its radio in a 48" diameter source [Jones, 1973]. Earlier infra spectrum is predominantly that of a non-thermal red observations with a 13" beam and tangent chop source, except that at high spatial resolution the indicate an upper limit of about 2 x Iff17 W/cm2 lo source splits into two components, one of which the line intensity (Aitken & Jones. 1972]. Recently Sgr A (East) is definitely non-thermal, while about at Tenerife, we have observed the source with a 25" one arc minute away Sgr A (West) has a much flatter beam and 27" chop and found a signal at 12.80 urn of spectrum and is consistent with being thermal, al 9.5 + 2.2 x HX' 7 W/cm2 (Fig. 5). The flux calibra though its brightness temperature would be uncom tion is preliminary, being based on the work of Woolf fortably high [Jones. I973J. Sgr A (West) is coinci & Gillett (Woolf, 1972) made with a similar beam dent with the 2.2 jim source of Becklin et al. 11968] size. As in the case of G333.6-Û.2, it is difficult to and the lOpm source at the galactic centre mapped estimate the effective emission measure in our beam; by Rieke & Low 11973b|. Detection of a Ne II line different assumptions tead to the values of neon from this source would be conclusive evidence as to abundance shown in Table 2- It is noteworthy that in its thermal nature. this case the He 109a line has not been detected and that the upper limit to the He/H ratio deduced from Sfll A «tat radio recombination Unes is less than 0.025, or less than about one third of the normal helium abun dance. The explanation that helium is not observed because selective dust extinction restricts the highly ionising radiation to a small central region which is discriminated against by the large beam radio observa tions, is given support by the detection of the neon line, since helium and neon have similar ionisation potentials. Spectrum of Sir A (West/in theregion of the neon line at IZSOfim. The dashed Une indicates the resolution of the spec trometer. 4> l>k All KIN. H HlMMl HI'NMAN ACKNOWLEDGE** ENTS We H on IJ like in acknowledge I hi' assistance ott Hunks are also due u. C <» Wvnn-Williarm. S Hants, ihe Matt ai ihr Rl.O and Kadditte ohsmalniirs. thhe jnd [l Allen tor useful discutons and loi results help ot K MSCUTJI at lenente. a..J technical awi* hmuglu lo oui attention prioi m publication by lana* trom \1 I'jliner o: the t'Ci Inttaicd Gioui|>p S Mains and h C (iilletl. who also JVMMCJ dunng MUIW ot ihc ohsonatiom REFERENCES 1. Atlken. I)K A Jones. H. ft,* I nM bumrvaii 6 Jones. IV. .Asirophrs. J (Utl.i. 14.47 | |'»7.1| Meeting IAI. W": * Merrill. K M & Stuler. B.l . AMrnphn J . IN9. U\A\I.V 165.363 (1973a). I 27 119741. .4srr«y»Avi J IM. i:".ll""-'h> h IViiMon. M.V. Allen. 1) A & Hybrid, A.R.. WVAM.V. 167.11«?41 Astrophvt. J.jLetl I 170. L33 ( l'"l ) .. Berlin. t K. t-togel. J A . Neugehauci. C. . IVrv >i Riekc. Ci.H. A Low. \-J..AUrophn. J . 184.415 son. S fc . & V>ynn-Williams. (G.. Astmphis J . (l«*73|. iLeit.i M1.L\25tW}\. .Utrnphys. J.. Wb. L7|ll>7.1| ? Bedclin. E.fc 4 Neugetaucr. G.. Asiroplivi J. 1(1 Shaver. P.A. & Gross. W.M. Ami. J fïivs. 1 SI, 1J5H96S) Astntphyi, Suppl 14. I (Itl70l 4 Gausiad. J.b . AiTf'Thyh J.. 138. 1050 H*»b3|. 11. Wooll. N.J.. IAU Symposium. New York. W71 5. Gdlen. h C & honest. WJ . Astmphys. /. 179. 483 (I*»"1?). DISCUSSION B. BALK K Sa« B-"a highly discrepant case in a low flux at about 12.5 or 12.0 jim. that no helium his been dtleded lo a level of I *# and the ionisation required to produce the H II region is S. ft)TT ASCII: In deriving the neon abundance enormous. I would like to suggest strongly that obser- have ynu ignored the higher stages of ionisa lion'' vation of this object be made in (he Ne II line. D.K. AITKEN: Yes. we have assumed that n is all J. MAYO GREENBERG: You attribute the two Nell. high points at i 2.8 ym in the Woolf & Forrest galac tic centre absorption curve to Nc II. Can you in'er S. POTTASCH: That may nul be such a good that the other (substantial) structure in their curve assumption. About half the neon may he in higher has significance'* stages of ionisation. D.K. AITKEN: We are only saying that the two D.K. AITKEN: We have taken the altitude that spectra are not inconsistent. However, both do show this is the least unknown of the quantities. 49 ON THE STRUCTURE OF MI7S CD. Andriesse &. I. Koomneef Kapleyn Astronomical Institute. Groningen, The Netherlands and European Southern Observatory. La Silla. Chile ABSTRACT The hehavioui of the 9.7 y m band due to dust This source is probably ultraviolet-photon-bounded, particles is siudied for some positions within MI7S. with cool dust in front. Al least foui near-mfrared sources aie associated The presence of the 9.7 pm band in absorption with the IIII region MI7 (Lemke & Low, 1972; points to cool dust in front of the source, which by Kleinmann. 197.1; Klemmann & Wright. 1973]. We absorbing at 9.7 pm will be heated above the inter have studied ihc spectrum around IQum for MI7S, stellar equilibrium temperature of 10 - 20 K. It is this winch is centred at a(l950)= I8nl7"i34s £(1950) = dust, which also is associated with M17N and 16" 13'20" and has a FWHM of about 2'. or 1.2 pc. M17SW, that is probably observed in the far infrared It is delineated remarkably well on the red Palomar (Ollhof, I974J. The source M17S therefore seems to Sky Survey plate as a very dark region in the western be ultraviolet-photon-bounded rather than dust- edge nl the emission area of Ha. Close lo the central bounded [Pottasch, 1974]. We find a peculiar beha m position is BD -16°4B 16 with V = 9.67 , viour for the depth o of the 9.7 pm band, o being m m B V = 1.60 and U - B = l.80 . Because of its introduced by Bergman [1973]. Going out from Ihe slight reddening this should be a foreground star, centre to the east, the band seems to weaken first, while the exciting object is probably invisible (cf. but then becomes quite strong near the edge. This Klcinmaiin, 1973; Johnson, 1973]. Th: aim of our should be interpreted in terms of warm dust in the study was lo establish the possible occurrence of an interstellar band at 9.7 /im due to dust particles and its dependence on position within the source. Table I Using (he 1 m ESO reflector, surface photometry was performed with a 30" circular diaphragm in spec Fluxes in Iff34 W m "* Hz"1 for a solid angle of tral filters al 8.1. 9.6 and 12.2pm with 10% resolu 1.66xl0"Bsr along o<1950)= -I6°I3'20'\ The tion. Flux gradients were measured with abrupt ('rec index o is the difference between the average 8.1, tangular'), rather than harmonic, beam switching 12.2pm magnitude and the 9.6 pm magnitude. (Koornneef, 1974] in right ascension over 30". Reference fields were taken 200" south of the decli 0(1950) = ^"n^and nation of ihe centre. The gradients thus measured can 34s 36s 38s be added from the edge of the source towards its 8.1 urn 4.8 1.8 0.9 centre to give surface brightnesses. They are cali brated to a Sco, for which, at the respective wave 9.6 urn 5.9 2.9 <0.2 lengths, magnitudes of -4.27m, -4.60™ and -4.70m 12.2 urn 34.2 16.6 8.1 are adopted. Some results are shown in Table 1 and m Figure 1. u 0.9 Ojm >3m Cil «NDRII SSI 4 J KOORNNI 1 t Dependence of absorption band at Figurt 2 Sketch of possible spatial structure in 9.7 pm on position in Ml 7S. Fhix refers MHS (see text for explanation f. to a solid angle 1.66 x Iff* ST. source and cool dust in front of il. A possible explan thus appears in emission and its strength increases ation is sketched in figure 2. towards the edge, where A becomes thinner. Became The photon-bounded region A is directly excited of foreground effects, however, this effect ii masked. by ultraviolet sources, invisible due ic at least 20 mag The fact that the band is absorbed more strongly at of visual extinction in A and in the foreground B. The the eastern edge than at the halfway point can be lOum extinction in B may be 2-4mag, depending ascribed to higher densities and larger optica) depths on the depth in the line of sight. At lOum, region A in B at the position of the shock, which is undoubted is not optically thick, and its optical depth increases ly moving westwards from the visible H II region. from zero at the edge lo some tenths in the centre. We hope to give a more quantitative description The colour temperature of about 180 K, based on the later. Clearly, study of the 9.7 ym band can add con 8.1 and 12.2 pm fluxes, does not change much siderably to our understanding of the structure o( through A, which implies that the dust has a rather compact H II regions. uniform temperature. For region A the 9.7 ym band ACKNOWLEDGEMENT We are indebted to Prof. E.H. Geyer for the t'BV for the lOiim atmospheric window which we used photometry of BD -16°4816. The band photometer has been built by Prof. 3. Borgman. ON TIM STKI'CIUKI-. Ol- MUS REFERENCES Biirgnun. J. .litron. J .•lirrsf/)/rri 29. 44.Ï 5 Konrnncel. J . m prépara In in D. Lemke Max-Ptanck-lrulilut fur Astronomie, Hcideiberg. Germany The observations J will present here were made ïo 10 nigh Is are "good" m terms ut sky muse. Ingclher wiih Dr. Low from the University of Arizo Let us return now to the example of MI7 and na. We intended to study several of the brighter and examine the usefulness of these measurements. Fi more extended H II regions detected by Harper & guie ? shows one of the radio continuum maps of Low 119711 three years ago in the far IR with the Ml 7, made by Schraml & Mezger 119641 at 2 cm 12-incli Lear jet telescope. wavelength. This map is very similar u> the 21 fim Now, before discussing the observations and some picture, except for a few details in the east. We can results. 1 will show you Figuie 1 as an example of therefore conclude that on a large scale the ionised these results. This is the Omega Nebula Ml7 as seen gai and the dust ate distributed in essentially ihe M 2! fim. This wavelength was the only one we used same way in this nebula. It should be noted, however, because il is the longest one routinely accessible that ihe ionised region on this map is much larger from the ground. Combined with the very large beam lhap on the 21 urn map. diameter of l', we were able to see the fair.t surface We have integrated the flux from our M17 map to brightness arising from the 100 or 200 K dust emis construct a thermal spectrum of this object. Figure sion throughout the nebula. From the a, 6 scale, one 4 shows the results. The 10 and Sum points are can sec that this map covets an area of more than 40' from measurements by Kleinmann 1197.1 J jr.d the square. There are two main sources (M17S and Tar IR data are from Harper &. Low [ 19711 and Hoff M17N) and a fainter source E in the east close to the mann, Frederick & Emery [1971]. Clearly, a single maximum of the Ha brightness. The angular resolu black-body curve cannot tit all these data. A model is tion obtained here is similar to that of most radio therefore postulate., in which two dust components maps and (hat of the recent far infrared maps made are mixed with the gas throughout the nebula. By from balloons. The 21 um brightness of M17 as well arbitrarily assigning half of the 21 um flux to each as of all other extended objects studied with the wide type of dust, we have derived temperatures of 240 K beam were found to be at least twice that obtained for the hot dust and 75 K for the cold dust. The earlier with smaller beams. Consequently, several corresponding luminosities are 10° LQ and parameters, such as IR luminosity, were affected. 5 x 10* LQ. With the usual assumption about the dia For this type of observation, a small telescope meter of the interstellar grains and a IA dependence could be used: most measurements were made with of their emissivity, the masses involved are 3 the 28-inch tHescope on Ml. Lemmon, and occasion 2x 10" MQ and 4M0. This is about 1/100 of the ally the 60-inch was used. Because of the combina hydrogen mass as determined by radio measurements. tion of the poor 21 um window, large beam diameter and a large chopper throw (1.3*), sensitivity was Table 1 severely limited by sky noise. Figure 2 shows the records of four different nights, with the same scale. The second record from the left shows (lower part) the signal of the Galactic 240 K 75 K Centre in the I ' beam, corresponding ic a 0 magni 10'Lg 5» 10* LQ tude of -6.6. Both outermost records are for typical Ixlff'M nights, with occasionally bad sky noise. Only I in 5 0 4MQ Figure 1 Contour map of Ml 7 at 21 nm. Isolines are in units • 1C1 * Wm~2Hz ' »•"'. Overlay on a 120-inch plate Perhaps this model is not entirely correct, but to seen at a distance of ~- I from the Trapezium. Note decide whether both types of dust exist inside the the scale; 21pm flux was obtained over an area a- nebula or a large thermal gradient with the cold dust bout 4' square. In Figure 6 also the most prominent near the edges of the nebula, one needs high-resolu- feature is the KL- Because of the wide beam, both liun tar IR maps. An increase in the size of the nebula sources could not be resolved separately. Neverthe with wavelength would favour the thermal-gradient less, the centre of the entire region seems to be the model Trapezium rather than the KL. In the west we found Another ohjoci that we have studied with the an extended faint source. This map covers an area of wide beam system n the Orion Nebula. M42. Figure 5 more than 60' square and may therefore be the larg ÏIHJWÎ ibis icgion as mapped hy Ne>' & Allen (19691 est 21 pm map made from the ground so far. with a _6" beam. Piete IS an extended source around The flux from the entire region was obtained by the Trapezium Mais, and at the bottom uf the figure integration of the map. The result is 1.5 x 10~2IW the well known Kleinrnann-1 .<>w nebula Figure S. Radio continuum map of MI 7 made by Schraml & Mezger. Figure 2. Kecords on four different nights of 21 um observations with the wide-beam system at the 28-inch telescope. WAVELENGTH (,, ) 300 30 3 The Orion nebula is therefore probably the brightest • SAG B2 , . MI7 21 Jim object outside the solar system studied so far. \ COLD OUST Now let us compare this infrared map with other maps. Figure 6 is an overlay on a photographic plate. \* • There is little or no correlation between the optical / // and the infrared. Figure 7 shows the radio continuum •' //NGC2024 M [7 map made by Schraml & Mezger [1969]. Except for . HOT OUST the fact that the KL is not to be seen in the radio / / \ 1 region, there is general agreement. Both maps show a ' / - / i bright source with the Trapezium at the centre and a 1 faint extension to the west, in the radio map a little farther away than in the infrared map. Again, like , OR 21 M17, the 21 Mm source is much smaller than the ion ised region. There are speculations that this might be expected if the dust absorbs an appreciable part of l (l the Lyman continuum photons emitted by the exci • M 17 ù SAG B2 ting stars. Because of the many uncen linties involved ONGC2024J in this problem 1 should not discuss it further here. OC3R21 Figure 8 shows an Orion map made in a CO line by Penziaset al. {1973I- There is little or no correlation LOG FREQUENCY (HZ) between the CO and the infrared, except for the faint extended source in the west. Thermal spectrum of if J 7. Data are for both main components (N + S). KOI WIDTH Q Figures MapsofM42a 10 and 21 vm tri&i). Mips mmdc by Neyi Alia. m 5*3nC 5'J2-»' 3-22"30' '/'iT 10' Figure 6. Map of M42 made with the wide-beam system Isolates are in units — 2 x HT17 Wm'1 Hz'1 sfl Unfortunately, up to now there has been no other this symposium {Fazio et al.; Simon]. Several months iafrared map of similar extent to allow the tempera ago we only had the 350 jim measurements of Harper ture distribution of the dust throughout the nebula to et a). [1972] for comparison with the 21 pm data. be derived. This situation may now have changed, as These authors had measured 350 tan fluxes of several far IR maps of M42 are to be presented during 1600 f.u. at three different positions north and south WIDl-'HkAM MKASUREMKNTS OF- II II KF.GIONS IN IK 57 h 10* 05*33m001 50* 1? 05 32*00*50* Figure 7. Radio continuum maps ofM42 made by Schraml & Mezger. of the Trapezium. We have averaged their 350/mi fluxes over the central lx 4' square field where they were obtained. With the 21 fan flux from the same Held, we could derive a colour temperature for the dus! of 102 K- for the case e independent of X or 70 K for a 1/A dependence of e. The KL was not included in the field considered. It was assumed that the flux of the Trapezium nebula at the position of the KL was the same as that 1' to the south of the Trapezium. With the further assumption that the 100 K derived for the central region holds for the entire nebula, we can estimate a luminosity of about ~ 4 x 105 Lpj. This is approximately the same value as the total ultraviolet luminosity (both Lyman • - and Lyman continuum photons) of the four Trapezium stars which were thought lo be the exciting stars of Figure 8. COmap ofM42 made by Penzias ei ai M42. On the other hand, only a smaller fraction of the Lyman continuum pholons should be responsible very recently with the wide beam system. In March for the heating of the dust. Further delays of the and April 1974 we rescanned Orion north and south 21 im\ measurements of M17, M42 and other objects of the region thai we had already mapped. Besides a are given by Lemke & Low (1971) and Lemke, Low further increase in flux, the final map will demon &Thum [19741- strate even more that the Trapezium is the centre of Finally, a few words about what we have done M42 at 21 (tm. We have also scanned the small nebula 58 D. LbMKK to ihc north east (M43Ï and have found it much for llic nebula even m the far IR. Finally, wc have brighter and moic extended than indicated by the scanned W5I with the wide beam. Reduction of all results obtained with smaller beams. This object these d3ta is in progress and I hope that the results might be suitable for a closer study of the energy will be of some use in combination with the new fai equilibrium in an H II region, because there is little IR maps of these regions which will bo presented at obscuration, the exciting star has been well investi tlirs symposium. (Sec Fazio et al.; Simon; Alvarez ci gated, and there are nov>- many observational results al-l- REFERENCES 1. Harper. D.A. & Low. FJ-. Astrophys. J. Lett., Astrophys.,32,231 11074). 165.L9<197]). 6. Kleinmann, D.E., Astrophys. Un.. 13. 49 2. Harper. D.A.. Low. FJ., Rieke.G.H. & Arm (1973). strong, K.R.. Astrophys, J. Lett., 177, L21 7. Ney. E.P. & Allen, D.A.. Astrophys. J. Lett.. 155. (1972). LI93(1969). 3. rUTmann, W.F„ Frederick. C.L. & Emery, FU.. 8. Penzias. A.A- A Burrus, C.A., Ann. Rev. Astron. Astrophys. J. Lett., 170, L89 ( 1971 ). AAstrophys., 11,51(1973). 4. Lemke. D. & Low, F J-, Astrophys. J. Lett, 177, 9. Schraml, J. & Mezger, P.G., Astrophys. J., 156, L530972). 269(1969). 5. Lemke, D-, Low. FJ. & Thum, C, Astron. & DISCUSSION A.F.M. MOORWOOD: What was the extent of ly, you are wondering about the small distance be the region scanned and how did you set the zero level tween the isolines as compared to the large beam size. in you. map of M42? This looks like fine structure, but it is not. The dis tance between the isolines is only determined by dif D. LEMKE: The region scanned was 15' in right ference in flux, the isolines are given in units of T 1 -1 ascension by about 7' in declination with the Trape 2x10"' W m" Hz sr"'. At the centre we have a zium at the centre. The zero level of the flux was strong gradient in flux due to the Trapezium and the adopted at the eastern boundary of this field. Only KL object The true resolution of the map is only in right-ascension scans were made. The true 21 urn the order of about l'. The beam profile was very source is probably more extended than the region close to rectangular. where we have seen flux. B. BAlJCK: Radio maps shew that much of the G. NEUGEBAUER; What was the increase in flux ionised gas in both Orion A and M17 is distributed in from M42 due to the new scans north and south of structure of size > ]'. Since the beam throw of your the area already mapped al 21 Jim? system is 1.3' could you comment on the effect this might have on the estimated total fluxes you derive at D LEMKE: 1 estimate 15%; the area is larger by a 21 pro? factor of J.5. D. LEMKE: Certainly, the total 21 fan flux P.E. CLEGG: What was your beam throw for the would have further increased if we would have work Orion mapping? How dH you obtain such a detailed ed with a larger beam and a larger chopper throw. But map. bearing in mind the beam size and the relation this experiment is very difficult lo do from the between the beam size and beam throw? ground because of sky noise. As an example, the 21 um flux derived from our M42 rtmp is a factor 4 D. LEMKE: The beam throw for the Orion map larger (if I remember correctly) than that derived ping was 1.3'. If I understood your question correct- from the Ney-AIIen map which is shown in Figure 5. W1PK-HLAM MILASURI-MI-NTS OF If II RfcGIONS IN JR 59 I'mhahly ilie I rye 21 pin source js 3s extended as the 3nd N at 2] pm? 2 cm rati it i map. Bui I can not say how much 21 pm llux would come from the outer regions. D. LKMKt: The integrated flux density at 21 um fut MJ7S is S.lxKT31 W m"1 H,;; for M17N it is 5. I'OITASCH: Whai is tlic total flux from MI? S 3.1x1er22 W m"3 Hz" FAR INFRARED PHOTOMETRY OF HII REGIONS I. Fumiffi, R.E. Jennings & A.F.M. Moorwood* Depart menl of Physics & Astronomy. University College London ABSTRACT Broadband 40 • 350#m fiuxe' enteil for with available radio continuum data, have been used 56 sources observed with the Un lege Lon to investigate further ihe reli nship between infra don balloon-bumi: telescope. Wj estimated red and radio flux and to estimate effective dust ab pointing accuracy, all of these soi can be identi sorption depths and dusi-to-gas ratios within the fied with H II regions. The measu, luxes, together ionised regions. I. INTRODUCTION Bmad-band fluxes from 40 - 350umhave been cluding soutce positions and contour maps obtained measured for a large number of galactic sources as Tor NGC 6334 and NGC 6357, has already been pub part of a continuing programme of far-infrared obser lished (Emerson, Jennings and Moorwood 1973. here vations using a stabilised balloon telescope built at after referred to as EJMJ and a similar publication University College London. The observations dis describing Ihe 1973 data is being prepared. cussed here were carried out during Autumn 1972 Intensity maps of WSI and ifcs galactic centre and Spring 1973 on flights from the National Scien region and a spectrum of G 49.5 - 0.4 in WSI, also tific Balloon Facility, Palestine, Texas. obtained on these flights, are discussed separately in A more detailed account of the 1972 results, in these proceedings. 2. OBSERVATIONS M INSTRUMENTATION The 40 cm aperture telescope and liquid-helium - gjve a beam throw of 5' in cross elevation only. Pre cooled photometer used were essentially the same *s viously, a circular beam motion was employed and described by Fumiss, Jennings and Mooiwood phase-sensitive output signals were derived in both 11972], except that between the 1972 and 1973 elevation and cross elevation. In both cases the chop flights (he method of sky chopping was changed to ping took place at the telescope secondary minor. A series of overlapping scans of the planet Jupiter Now will iht Autonomy Division. Furopcan Space were made to determine the flux sensitivity and beam Research Organisation. Nootdwijk. Tin' Nctticrbmis- response of ihe system and HPBWs of 3.5' and 4.0' ] rilRNISS, R.I. JtNMNCSJL A.I-.M. MOORWOOD respectively were measured foi ihe two sets of flights Jenl with lliermal galactic radio sources. Positions were determined by scanning each sour In Table I we have used the radio ii numbers lo ce a number of times to locate the star tracker offset identify the sources and have included both far-infra co-ordinates corresponding lo the position of peak red and radio-continuum data, For most of the ob infrared flux. Any systematic errors due, for example, jects, the infrared and radio positions agree lohetlcr to an imbalance in the gondola or 10 the presence of than 3' and the largcsl difference is around (•'. The more than one star in the field of view of the siat peak 40 - 550pm (luxes quoted assume a 155 K tracker were corrected for using the positions of black body spec I rum for Jupiirr and a colour tempe visible stars viewed by the focal-plane optical dctec- rature of 80 K for the sources. Varying ihe tempera IOI. Undsr favourable conditions, this procedure gives tures by + 10 K and + 20 K respectively, produces a positions within an estimated r.m.5. error of f. h is maximum flux change of + 20"". Other factors affec difficult to achieve this accuracy for weak sources or ting the accuracy of the fluxes aie difficult to assess, when observing at large offset angles. hul in the case of one of the sources. G 1.13.7+ 1.2 in W3, measurements made on three separate flights yield fluxes which are within \0T<. The infrared sizes quoied ate approximate values estimated from the widths of the recorded signals. All the infrared sources observed on these flights Analysis of all the data in respect of size information appear, within our pointing accuracy, to be coinci- has not yet been completed. 3. DISCUSSION OF RESULTS 3.1 NATURE OF THE INFRARED SOURCES ticated models to explain the observed properties of the sources. Such an analysis is beyond the scope of The infrared sources listed in Table 1 have all this discussion, however, where we shall restrict our been identified with H 11 regions exhibiting thermal selves to a mote general interpretation of the obser radio continuum spectra. Some of the objects have vations of a large number of objects in terms of the visible counterparts, but most are heavily obscured in model described in the following section. the visible • either by interstellar dust or by dust in front and local to the objects. Where infrared sizes have been measured they ate dose to the radio sizes 3.2 DUST MODELS FOR HII REGIONS and in the cases where more detailed maps have been obtained, eg. NCC 6334 and NGC 6357 (EIM), W51 Table 1. 40 - 350 tim and radio continuum data ::;:::] ::;::d JD4(M IÏ 2MS} n-MS) t_> IS. MS) u.t «•KS) V.I »aj) Ul. «HSl ».: uas) IJ 0.9 il-HS) :j 3.1 o.MS, iJ 1.3 MSI *.B 4.7 9W} l.< 1.6 *.«i7) 44.9(S) 0.9 as I7ÎJCS) l-> ii -'A«S) X3 is u||U7u| J. Ktritmitm « iL ||17U]. J. LrudciiL |l*,|. S. Alrenholli Iniml«k*l#fr|l3t><»]. s rs* broad-band intured 11 uv and radio continuum llu\. which has been interpreted a;, evidence that IIM- primary wuia1 of the infrared energy is the main sequence ionising siarts) of the H II regions. In Figure 1 we diow thai although there is still a general correlation, no -ample relationship between i he infrared and radio fluxes appears to hold for (he larger sample of objects now observed. Some features oï this plot can probably be explained in terms of evolutionary effects. Young, compact objects fot example ma> contain pre-main sequence or recently evolved stars and can be expected to possess a higher ratio of infrared to radio flux (e.g. G 153.7 + 1 ,T and G 133.** + 1.1 in W3. sources A and 4al than more evolved regions. Most of the objects observed, how ever, are well developed H 11 regions and we account for most of the variations in Figure I in terms of differences in the ionising stars and the dust optical depths inside the H II regions. (iii) Dust optical depth A useful quantity which can be determined from RAOW CONTINUUM FlUX (l.u) the infrared and radio observations is the ratio Rn of the total infrared luminosity to the Lyrtrn a energy produced in the H 11 regions. Figure I. 40 - 350 (im flux verves radio continuum To allow for the energy radiated below 40 ;rm the flux. References for the radio fluxes arc luminosities given in Table 1 have been increased by a given in Table J. factor 1.4, equivalent to assuming a colour tempera- [Conti & Alschuler. 1971] and temperature [Conti, lure of around 80 K for the integrated output of the 1973] scales and the NLTE model atmospheres of sources. The Lyman a energy has been taken as Auer &. Mihalas [1972], It is immediately clear that a large fraction of the sources observed must contain LLyo = 10" tfSrtuOa clusters of stars or consist of unresolved groups of objects. where D is the distance in kpc, S the radio continuum The fraction f of the stellar Lyman continuum flux in f.u. and (luOa is the energy of a Lyman a photons absorbed by gas inside the H II regions can photon. This expression was derived from Rubin's be determined in a straightforward manner from [1968] relation for the ionisation rate of H II regions Figure 2 if it is assumed that the stellar and total with Te = 7500 K and under the assumption that infrared luminosities are equal. (The fraction of every hydrogenic recombination gives rise to a Ly Lyman continuum energy absorbed is also equal to f man a photon. (The analysis which follows is not in if the grain absorption efficiency is constant below fact sensitive to this assumption) 912 A). In this case In figure 2 Ra is plotted against infrared lumi nosity. The highest value plotted (~ 38) is for 1R luminosity _ LsTAR W3(OH). which is probably the least evolved object Lyman a luminosity n (hf)a included. The source associated with the OH mascr in NGC 6334 is probably higher than this, but a radio continuum flux cannot be assigned. where 1^ is the number of Lyman continuum pho The spectral types indicated along the top of tons radiated by the star per second. The L-H side of Figure 2 are for ZAMS stars with luminosities corre- this equality is Known from the observations, and '^onding to the infrared luminosity scale. The stellar ^-STAR/Lc fr°m tnc a^op160* swU" model. iuritnosities and other spectral data used have been Having determined I, the optical depth below taken from the tabulations ofPanagia |I973], which 912 A of dust inside tne H II regions can be calcu aie based on recently derived absolute magnitude lated either by using the analytical expression given 1-A.R IR PHOTOMETRY Ol il II Kl (ilONS BO 09 01 07 06 OS 01 w ]• \ M \ V > »» \\ \ 3 10 \ f » It'O \ y 3 ?6 \ 2t \ \ 1 \V« s " JIB 10 \ < S I '* HA ' 30 - 16 \ v ~ 1* ^^. HA z 'Î """-»_» 32 """—-i. * ID g —-JO _ 19 26 " 3» a1 ''° 6 ? "J, * « 12 IB „ £0A 5 C ""---i-__J£Uj* 21 * 25 K g *° z * to 2 35 UJB J 3*5 I 3 15 2 3 t 5 INFRARED LUMINOSITY (L/L«) Infrared access as a function of total infrared luminosity. The spectral types shown are for ZAMS stirs lioying luminosities given by the infrared luminosity scale. The curves for r = 0. I and 2 are minimum values of the dust absorption optical depth {below 912 A) inside the H II regions. by Petrosian. Silk & Field [1972] or more simply and made in determining these optical depths, that the with results closer to numerical calculations of Mathis infrared and stellar luminosities are equal. Except for [1971] by assuming possible size effects, this amiiDption it reasonably wi ld if the HII regions are surrounded by dust which is optically thick at ultraviolet (>912A) and visible wavelengths or when the internal optical depths are Here rrjy must be interpreted as an effective dust high. absorption depth as the effects of absorption and On the basis of Figure 2, the only objects incom scattering have not been separated. patible with such a model are those which rail below Curves coirssponding to ryjy *= 0,1 and 2 are the rtry = 0 curve. In fact, all but one of these shown in Figure 2. Assuming the objects to the right sources (no. 40b in the GC region) are associated with of these curves to be ionised by clusters of average visible regions, as are most of those which lie close to spectral type OS the same optical depth values corre the TTJV = ° curve. It is likely, therefore, that in these spond to values of Ra equal to 3.9, 10.6 and 29, cases the stellar luminosity exceeds the infrared respectively. (The values for any other assumed aver luminosity. age spectra] type are equal to the values of Ra at the Calculation of the true optical depths, however, intersection of the required optical depth curve with requires additional information with regard to the the luminosity of a star c the assumed spectral type.) dust absorption properties. Panagia [1974) has re For all but a few of the objects therefore, the cently analysed the problem of calculating dust opti dust optical depth inside the H 11 regions lies in the cal depths under various assumptions concerning the range 0 - 2, with & mean value of around 0.8. (As no distribution and absorption properties of the dust. In scaling of fluxes with respect to size has been per view of the large uncertainties involved, however, we formed in these particular calculations, the actual estimate the change in these cases by considering a values could be 'ligher fur some of the objects.) It is simplified model in which the dust optical depth is appropriate at this point to recall the assumption assumed constant over the stellar spectrum inside the I 1-rKMIKS. R-K JFNNlSf,S A A I'M. MOURWOOI) ;%.'*, INFRARED LUMINOSITY. (L/L.) Figure 3. Dusr-to-ges ratio plotted against total infrared luminosity. Where sources are plotted with error bars the upper and tower values correspond to zero and infinite VV (> 912 Ay and visible dust optical depth outside the HII regions. For the remaining sources the dust-to-gas ratios are fairly independent of the optical depth assumed outside the HII region. 3 HII region and zero outside. The Lyman a radiation ryv = Ouv * â NdR is assumed to be completely absorbed by dust within the HII region, while all the remaining nebula pho where Q|jv >s ,ne effective absorption efficiency of tons escape. Under these assumptions, we have the ;he grains below 912 A,a is the grain radius, N a 1 Md -5- * z=- apR In Figure 2, the lower curve now corresponds to TTJV or Quv ~ 0.6 and the others to Tijy = 1.25 and 2.1, respec 3 tively. Only the low optical depths are significantly Md/M0 =532— ap^D affencd and the mean optical depth is now i. The Quv ionisation of the regions is clearly affected by the presence of dust therefore as, typically, only one where p is the density of the grain material (g/cm3 ), third of the stellar ionising photons are available for a is the grain radius (cm), © the angular size of the ionising the gas. H11 region (arc min) and D is the distance (kpc). The mass of ionised hydrogen can be approxi mated ISchraml &. Mezger, 19691 by (rv) Dust-to-gas ratio Mg, In principle, it is possible to estimate the mass ratio of dust to gas inside the HII regions required to explain the dust optical depths. For a uniform distri where S is the radio continuum flux (f.u.), 3 the bution of dust inside the H II region. angular size (arc min) and D the distance (kpc). I AR IK PIIO'lOMI-.TiCOMf II HKiJONS G 7 Tliito (ii) "high' luminosity 02x10*1^) objccis am with low dust-io-gas ratios and (iii)a group of medium luminosity objects wi a range ol dust-lo-gas raiios which show some t- n- dency to decrease with increasing luminosity. The decrease in dust-lo-gas ratio with mcrca-.. Dusi-io-gas ratios calculât cil with p • 2, a = luminosity cannot he pursued very strongly on U. o x I If'' tin and 0( rv = ' ;irc shown as a function (it 1 basis of Figure 3. Such an apparent decrease could infrared tummosiiy in Figure 3. result, however, from a dependence ol Qjjy on stellar All the values obtained are below I0'1. and ihe•: luminosity il the absorplion efficiency of the grams J average is around 2.5 x I0" . The vainc of a/0|jVf decreases rapidly below ''12 A. In tact. Me/ger et al could lliercforc be increased somcwhal without re |1'>74| have recently argued for an increase in Oijy quiring dust-io-gus ratios higher than the accepted1 below 504 A on the basis of an anticorrelation be interstellar value of around I' ; tween infrared excess and the He"*7H+ ratio. Where the value assumed lor the dusl opticalI The low dust-to-gas ratios tound lor ihe hi all- deplli outside the H II region has a significant effectt luminosity objects may he due m these sources hcing on the dust-tii-gas ratio, values corresponding to bothi multiple or to the distances being overestimated In zero and infinite outside optical depth are shown. Inl hotti cases the quantity lfl/SI))- tends to he under- the case of the object l'< 333.fi • 0.2 (source number r estimated. Higher spalial resolution ot these otnecls m 22). the dusl-to-gas ratio ot 2.S 5 x l(T4 is close toi requited therefore before this method can be applied the value of 2.5 \ 10 4 obtained b> A it ken & Jones> reliably. For the case of N identical, closely grouped |1'»74| tor 'he central region using an entirely diffe ob|ects. however, the dusl-to-gas ratios should only rent approach based on an analysis of the K-I3fmil increase by a laclor of -N'f The dust-to-eas ratio emission specirum. estimated for Sgr A I40h) is probahly too low be- The ohjecls in Figure .1 fall looseh into three: cause ihe radio flux used includes non thermal emis main groups. sion. It a Mux of 30 l.u. is adopted lor the thermal emission from Sgr A west, then the dust-to-gas ratio is (i| "low" luminosity ob|ects which have visible coun s increased to •HO""' terparts and low. relatively uncertain, dusl-lo-gas ratios: 4 CONCLUSIONS The far-infrared outpul of the objects discussed of olher extended regions, however, show a good cor appears to be satisfactorily accounted tor by models relation with ihc radio continuum maps indicating involving the heating of dust grains by main sequence that the infrared emission is centred on ihe ionised ionising stars. In some cases, however, there may be gas rather than on associated molecular clouds. Ultra addilinnal contributions in liie grain heating from less violet dust absorption optical depths of around unity evolved or even protostcllai objects of the type delec estimated for the H 11 legions suggest thai around ted below 20jini by Wynn-Williams et. al. \ l<>72 and 30-40'.; of the total infrared radiation and a some t'J73|. These objects exhibit OH and/or M30 maser what higher fraction of the energy beyond 40 ^m emission and have either no or extremely weak radio may originate in a neutral region surrounding the continuum emission. In the case of NCJC 6334, we ionised gas. The dusl optical depths required are com have evidence for the associuliun of one of the far patible with dust-to-gas ratios inside the H II regions infrared sources with an OH maser. Far-infrared maps which are lower than the interstellar ratio. ACKNOWLEDGEMENTS We wish to thank W.A. Towlson. T.E. Vein's, R.W. help before and during the tlights and the personnel Catch, F. Want. A.M. Walts and J.A. Alvarez for their of the NSBF in Palestine, who were responsible for €S t. J-HRNISS. R.t JINNINUSjl A.K.M. MOORWOOD llie bunches. Thanks arc also due to J .P. Emerson for T is pmgranime is supported in pari by an SRC his comments during the preparation of this paper. grant. REFERENCES l.Aiikcn. D.K. & Junes. B. ALXRAS 167. II 15. Malhis. J.S.. Ap. J. 167. 261 ( 1971 ). lb. Mezger. P.G., Smith. LF. & Chuichwell. I B.. 2. Altenholf. WJ.. Down». D.. Goad. L. Maxwell. Atfmn. S .\p. 32. 2o9(1974). » A. & Rinehan. R„ Astr & Ap. Suppl. 1, 3I<> 17. Panagia. N.. Astron. J. 78. 929 < 1973). 0970». 18. Panagia, N., This Symposium. 3. Alvarex. J.. Fumiss. I.. Jennings. R.E. King. K. & 19. Pctmsian. V., Silk, J. & Field. G.B.. Ap. / 177, Moorwood. A.F.M.. Bus Symposium. L69(1972). 4. Auer. LH. & Mihalas. D.. Ap. J. SuppiSer. 24. 20. Radhakristinan, V„ Goss. W.M.. Murtay, J.I). & 193(1972*. Brooks, J.W.. Ap. J. Suppl. 24.49 0'>72,. 5. Beard. M.. Thomas. Mac A.B. & Day. G.A.. Aust. 21. Reifensiein, E.C. 111 ., Wilson, T.L. Burke. B.F.. J. Phys. Asirophysical Suppl II. 27 < 1969). Mezger, P.G. & AUenhoff. W.J., Asrr. A Ap. 4. 6. Caswell. J.L.,-4wir. J.Phys. 25.443(19721. 357(1970». 7. Conti. PS.,Ap. J. 179. 181 (1973). 22. Rubin, R.H../lp.y. 1S4. 391 (1968). 8. Conti. PS, &. Alschuler, W.R.. Ap. J. 170. 325 23. Rubin. R.H. & Turner. B.E.. Ap. J. 165, 471 0971). 0971). 9. Day. C.A.. Thomas. Mac A.B. & Goss, W.M 24. Schraml. J. & Mezger. P.G.. Ap. J. 156, 269 Aust. J. Phys. Ap. Suppl. II, 11(1969). (1969). 10. Emerson. J.P.. Jennings. R.E. & Mourwood. 25. Shaver, P.A. & Goss. W.M.. Aust. J. Phys. Ap. A.F.M.,Ap.J. 184,4010973). SuppL 14,133(1970|. 11. Fumiss, I.. Jennings, R.E. & Moorwood, A.F.M., 26. Wilson.T.L, Mezger, P.G., Gardner, F.F. & Milne, Ap. J. (Lelt.f 176. LI05 ( 1972). D.K., Asir. & Ap. 6, 364 ( 1970). 12. Goss. W.M.. Radhakrishnan. V.. Brooks. J.W. & 27.Wynn-WiUiams, C.G. & Becklin, E.E.PASP&b, 5 Murray, J.D., Ap. J. SuppL 24. 123 ( 1972). (1974). 13. Harper. D.A., Preprint. 28. Wynn-WiUiams. C.G.. Becklin, E.E. & Neugc- 14. Harper. D.A. & Low. FJ.. Ap. J. (Lett. 1165.1_9 bauer, G.. MJVRAS 160, I ( 1972) and Ap. J. 187. (1971). 473(1973). DISCUSSION V. PETROSIAN: An alternative explanation for of calculating the dust-to-gas ratio is very uncertain? the points lying below the r - 0 line in your Figure 2 is that these nebulae are optically thin to Ly-con- A.F.M. MOORWOOD: I agree there may be un tinuum photons. Le. they are density bound. certainties in the stellar mode) adopted and the value of a/Qijv assumed for the grains. The estimates of A.F.M. MOORWOOD: This is certainly a possibi dust-to-gas inside the H 11 regions however should still lity, but we have assumed thai it is more likeiy that be more reliable than those obtained by assuming a the objects aie radiation rather than density bounded. temperature and far infrared emissivity for the grains - particularly if part i.f the radiating dust is mixed E.E. BECKUN: Is it not true that your method with neutral gas outside the H II region. 69 FAR INFRARED OBSERVATIONS OF W5I AND THE GALACTIC CENTRE J.A. Alvarez, I. Fumtss, R.F. Jennings, K.J. King & A FM. Moorwood* Department of Physics & Astronomy. University College London ABSTRACT Spectral observations of W51 as well as maps of 40-cm diameter balloon-borne telescope system are W51 and the Galactic Ont a1 region in the 40 • presented and discussed. 350 pm band obtained ftom observations with a I. INTRODUCTION During a series of balloon (lights made at NCAR, tely in these proceedings. Palestine, Texas, in the spring of 1973, maps were The University College London stabilised tele obtained of W5I and also of the Galactic Centre scope has already been described in the literature region in the 40 - 350 pm band. In addition, a low |Furniss, Jennings & Moorwood, 1972; Tomlinson, resolution spectrum (32 cm'1 apodised) was obtained Towlson & Vénis, 1974; Jennings, 1974|. The main of the main component of W51 (G 49.5 - 0.4) using a modification since the previous flights was to change Michelson interferometer. The broad-band photo to a linear 'chopping' system, which is more conve metric measurements which were made of a number nient than a circular *chop" for mapping and inter- of sources during these flights are presented separa- ferometry. 2. WS W5I is a highly obscured region which is known the system being known from scans over the planet to consist of a number of compact H II sources. Two Jupiter, which was used for calibration ( 135 K) and is raster scans of the region were made, the first having effectively a point source to our beam. The signals fifteen individual scans and the second eighteen, the were only deconvolved along the scanning direction scanning direction being approximately along the line and not perpendicular to it, the effective beam size of the sources. The data were deconvolved using (HPBW) being 4.5 and 5', respectively. A regular grid Fourier-transform techniques, the spatial response of of data points was constructed from the individual scans and used to draw the contour maps. The use of two separate sets of scans was found to be a great " Now with the Astronomy Division, t-uropean Space advantage as it helped to distinguish betweenjeal and Research Oiganisation, Noordwijk, The Netherlands. instrumental drifts in background level. The final map 70 ) A Al VAKI / I T Al t' l-'ig. I » is, ii> fact, a simple avetace ol' the two sets ol Tible 1 observations, the contour unii being O.tWx l(T'° W IjGlb hy Schiainl & Me/gei |1*><>°|. and u *.an he Peak flux Si/C seen ihji in gcneial iheie is very close agieemeni Component |\ 1(J10 W/m1» ,>»,•„,, between the infrared and radio contours. boi the tour num components ilie radio and (, 411.5 0.4 M) 3 5' x 4 5' nitrated poMtions agree in within 2'. except in The l .ase ol" G 4S ^ - 0.?. where the nitrated map tails to G 4».4 0.3 19 5 d' ie.%t>Ive ibis component trom the small radio sou tee r.4'1.2 0.4 12.5 I' G 4°.0 0.3 and the contours enclose both sources. G4.V ll.'< 14.0 <•' A* - »> ol the .same mdet as the positional errors of the infrared system, the results arc consistent with : fluxes to ' 20 Sues corrected lor beam width the mtiaifd and udio sources having common ceinte» tt'5! is known io have molecular clouds, and it the inliared soutces are associated with them iliev 2 I (.44 5 (14 c «uld be displaced relative to the centres of the II H regions; unfortunately. much higher positional accur The mam component G 4*) 5 -0.4 is known I torn acy is requited to deiermine whether or not this is the the high-resolulion observations ol Martin ]1972| • at 2." Gil? and 5 Gil/, to consist ot at least eight sepa rate radio sources, of which ihc toiu stiongcsl lie The dashed lines in Figure 1 indicate the leeinn within a circle of radius about I!;' and account lor scanned, and lor clarity only the higher contoiii". have ; over S5' of the radio flux. Ideally, each ot the sour been shown. There is no evidence for the small radio ces should be discussed separaiely. but the angular source (i 4*>. I - 0.4. although rliis is known u> have resoluiiiiii m the fat infrared is mil high enough lo H Wo emission (Wilson. Me/pet. Gatdmi & Milne. allow this and instead a simple spherical model loi 1970]. The optical depth of (he H II regions lor dust llie whole region is adopted. In Figure 3. measure absorption ot the Lyman continuum photons has ments ai different wavelengths have been ploited in been estimated m the manner described in the pre an attempt io establish the overall spectrum. The vious p3per and found to be one or greater. It lollows curve shown is for a colour teniperaiure of 100 K thai the infrared emission comes predominantly from (determined nom Micheison spectiouwiry) and nor the H II regions themselves rather than from outside, malised so thai the flux between 40 and 350 pin although the possibility of hottc inner dust re-radi- equals ihat determined in phulometry. The points at aitng to an outer shell cannot be excluded. 10 and 20urn are lite combined fluxes for just the The peak infrared fluxes for G 49.5 - 0.4 and iwo snun.es W51 - 1RS! and 1RS2 as measured by G 49.5 .0.3 as determined from the map are 60 and Wynn-Williams, Hecklin &Neugcbauet [1974|. These 19.5 x 10"10 W/m! for our band (40 • 350mn). two sources ate in excellent spatial agreement with Where appropriate, a background level (always two of the principal radio sources observed by Marlin < 20'.-1 has heen removed. Tltcse fluxes are m reason ||972|. Similarly, the measurement at 294cm"1 by able agreement with valuer of 64 and 12 x 10~1C Lou. Riekc & Armstrong []'>7.î| with a 12" beam W/m2 obtained by Harper&. Low ll°71| lor a 45 - will not represent the total flux fiom this region. The 750 ym band and an 8.4' beam. point (ringed! ai 100cm"1 is due in Hoffmann. Frederick & Finery |l97lb|. that al 2K.dcm"' to Table 1 gives the important infrared parameters Ricke. Harper. Low &. Armstrong 11973]. and thai at for W51. The sizes quoted are for sections normal M 7.ocm"' to Adc. Clegg & Rather (preprint|. The last the direction along which the components of W5I four points have been scaled and it is hoped that the lend to lie. except for G 49.5 • 0.4 where the sizes are procedure adopted is not too unrealislic. The radio fur sections both parallel and normal lo this direc points are from Dowries. Maxwell & Kim-hart tion, respectively. The values obtained correlate bet |I970], Hohbs & Johnson J1971J. Schraml & ter with the widths measured by Shaver & Go's Me/ger ] 1969| and Shaver & Goss | ll»70|. The slope [ 19701 at 5 GHz than with measurements at higher of the spectrum on the long-wavelength side of the frequencies; however, they arc subject to considerable peak is greater than that of a Flanckran curve and errors due to the size of beam used. corresponds to an cmissiviiy which decreases faster The peak fluxes have been calculated relative to than I/A. Jupiter (135 K) assuming a colour temperature of 100 K for all sources. F-AR 1R OBSERVATIONS OF W51 A GALACNC ŒNTRfc h m s gh ttlQ 5 19 21 00* 40 20* t 20 0 RIGHT ASCENSI0N(1950| Figure I. Far-L-ifrared map of W51. Contour unit: 0.69 x Iff* ° Wfm1. ) A 4IVAKIZ 11 AL Figure 2. Radio continuum map of W51 fSchrtmd & MezgerJ. Contour unit is^2 K (brightness tempera ture). f AH IK OIISI KVAÏIDNS Ol WSI A The scries nl' points between 100 cm'1 ami -50tin1 in Mgure .1 correspond In ilic low-resolu- mm spectrum obtained during the lliphis using a Mkliclson inicMcrririielci [lie background radiation from the lelrscopo was eliminated by llrsi hnUIiitc the M-.ii ILI' iti one heam and UIL'II in ilk' oilier ut I he Imcir chop. Ihc difference between the i«c spectra giving in principle twice 11 if spectrum ol the source. Hit* efficiency with which we were ahlc in do itits was determined b> comparison with (he spectra obtained with the MiuiLt* in neither beam. The agreement with the 1011 K mrvc normalised from ihe photometric measurements is reasonable good, showing thai llie parts ni the calibration procedure peculiar to the MichelMin unmil be in fcirf.it error [he scjns o[ the moving minor were ol limited duralion and I tie apo- dised resolution obtained was M cm ' The measured spectrum was best lined by a colnui temperature nl ' 1 1(H) K • 1 *> KL. which was the temper JILITC adopted tm Ihe curse shown in hgure t Diffraction eUects ai the (>' star stop should be small hut would lend to result in a higher colour temperature, which may partially explain why the value obtained was a little higher than Hie value ol 701 + 2(1 15 KI obtained hv Figure J Spcarum <>f w$l. Haiper & low [ l'»711. The error hars shown are sta- Ustical only and it can he seen that, allowing lor ihis spread, the points do not lie on a smooth curve. This 200 cm"1 similar to those observed, but somewhat is not lliought to be an instrumental fault as the spec displaced, possibly due to impurities. In this anal>sis trum of Saturn laken on the same flight did not show the rather gross assumption has been made that ihe similar lealurcs and we have a Hemp ted to see wheth dusi density in the H 11 region and outside is ihe er or nut such fluctuations could he explained by the same. Then, using the sizes quoted by Schraml & pec ul antics of any particular lype of grain by calcula Mczger 11**6*>| for the M II region and those quoted ting the emissivity lor different materials. Unfor here for tl.e infrared, the diameters of the grains for tunately, optical data is not available for many male- optimum fit arc 1 pm lor ice and 1.7 /im for sili nais in this wavelength region but Perry el al. [1972] cates, ihe corresponding dust-to-gas ratios for the H 11 give values for silica les and data for water ice is given region being 0.4^ and 2.2'T. respectively. Whilst the •n Hie review of Irvine & Pollack |I«)6S|. Various dust-to-pas ralio is not unreasonable, the diameters of grain lemperatures were considered and the particle the grains are larger than might be expected. How sue adjusted to give optimum fit. It was tound that ever, such sized grains have been found in some parts for a grain temperature of 48 K both watci ice and of interstellar space [Johnson. 1965; Jones. 1972]. silicates gave reasonable fits to ihe data, with water 1 Points raised in this analysis are being considered ice showing fluctuations between 100 cm" and further. 3. GALACTIC CENTRE Fifty individual scans were made of the Galactic map (Fig. 5) at 5 GHz of Whiteoak & Gardner Cenlre region, the orientation of the Galactic Centre [1973] with a smaller beam (4') shows that many of al (he time being such thai each horizontal scan of the radio features are reproduced in the far infrared. the alt-az mounted telescope was almost parallel to As well as the main components, Sgr A, Sgr Bj, Sgr C the right ascension axis. The resultant map after and Sgr D, there is a marked similarity between the dcconvolution is shown in Figure 4, the angular reso contours to the north of Sgr A and the two small lution being 5.6' (HPBW). Comparison with the radio radio sources to the south of SgrC (marked with J \ Al\ \R1/ Il AI GALACTIC CENTRE REGION (40-350m.c'onsl 17*«" 17*43" RIGHT ASCENSION 11950) Figure 4. Far-infwJ r.*it> of the Galactic Centre region. Contour unir: (J.V5 x 1 o -- i9*00 - Right ascenston(1950) Figures. Radio-comimmm map of the Galactic Centre region/Whiteoak & Gardner/. temperature of 60 K for the source. Only the higher sponding to the background is fitted to the wings contours have been shown but weaker contours indi where the central source has little or no flux while cate thai the far-infrared sources are extended. the gaussian representing the central separated source An attempt has been made to separate the flux of is fitted to the half-power points of this component. the principal sources from the background by taking This procedure worked quite well, the amplitude of a section through each source (at constant decli the background for Sgr A being greatest and falling nation, using the full set of contours) and fitting the by &% and 24% to Sgr Bi and Sgr C, respectively. resultant curve to two gaussians. The gaussian corre (For Sgr A the amplitude of the background was 37£ 7(J J.A. ALVAW-7. IT AL Ta h le 2. Infnrcd data far the Halaciic Centre Peak flux Sue L-, LjLç, &>uw !0'°\\/n.: (r-WHl'i HFK 40-350um ate nun 40-350*mi (75 • JJ5 J«II> Spr A 4S 7 31.5 x 10* 74(1 -c 10* Scr B- 34 3 l.illx 10* 3l(lx Iti' SgrC 16 6'Î I20x I0% :iK)\ IU* Di>t ance 10 kpc nf the peak height). However, the assumption ihat This is not necessarily inconsistent as the fluxes have two gaussians can represent the combined source in been separated from llie 'intensity ridge- vhul' tuns this way is questionable and. apart frum the influence from Sgr B- to SgrC and arc considerably smaller on the results of the exact procedure adopted, it than the values quoted hy HFE. Unfortunately, underestimates the integrated luminosity of the size determinations are not very accurate, parliculaily separated component by about 1S'7. Ibr sixes smaller than the beam - although the small Table 2 gives the separated fluxes, siws and inte value for Sgr B2 could well be in error, it is in fact grated luminosities of the main components and in good agreement with the si«: of 3' (15.5 CHzl includes the luminosities obtained by HFt 1197]a]. quoted by Kapiuky & Dent [1 4. CONCLUSIONS The maps of the Galactic Centre Region and of ing radio maps, indicating that both types of source W51 show a striking correlation with the correspond- have a common origin. 5. ACKNOWLEDGEMENTS We are very pleased to have this opportunity of discussions with Mr. J.P. Emerson during the prepa once again thanking the NSF and (he personnel at the ration of this piper. NCAR base for flying and recovering the payload foi This programme is supported in part by an SRC us in their usual efficient manner. We are also very grant. Messrs. J-A. Alvarez and KJ. King hold SRC grateful to Dr. Towlson, together with Messrs. Studentships, Dr. I. Furniss is a SRC Research Assis R.W. Catch, F. Want and À.H. Watts, for preparing tant, while Dr. A.F.M. Moorwood held an 1851 Re the system and providing such valuable assistance dur search Fellowship. ing the series uf flights. We are also appreciative of I AK IK OI1S1 KVAJIUfcSOl W51 A (lAIACfK OMKI 77 REFERENCES 1. Ade, P.A.R.. Clcgg. P.tr. & Rallier, JIM... Pre phys.J .\H\ L105(I973.) print ti> br submitli-it u> Astrtiphyy J 14 Martin, AH.M .MMiAS. 157. 31 (19721 2. Dowries. I).. Maxwell. A. & Ruieliait. R . /Iwm 15 Perry. (.11.. Agrawal. D.K., Anastassakis. I... fj/M'T./,161.1.123(1970) Lowndes, R P.. Kastogi. A. k li-rnherg, N t.. Vu- .V Furnirs. I., icnnmns. R.(. & Miinrwnmi. A I M . M,-i».4.3l5(l<>72j. Amrophys. J., 176. 1.105 I 1972) 16 Rieke. G.H.. Harper, DA. L.-.w. M & Arm- 4. Harper. DA.. Preprint. {I97.U Nlronp. K.R.. Asm'phyy J..] Hi. L(i7|l'»73). 5. Harper. DA. &. Uw. \-.S. Asrr, DISCUSSION D. LEMKE: Could you comment on the beam R.E. JENNINGS: The extended component of priifile and what determines the beam diameter (dif this infrared radiation from the Galactic Centre lias fraction, stabilisation)'' always been a problem to deal with, particularly with a differential chopping svstem. To reduce the effect R.B. JENNINGS: The beam profile is determined of small drifts, it was convenient to separate the over by observations on Jupiter(modified by the decon- all source in this way, but I think it is doubtful whet volution procedure) and turns out to be a good her they represent physically different regions. approximation to a gaussian. The star slop size (5') We have tried a I/rlaw fit. but it is not as good as was chosen relatively large because of diffraction and that obtained with two gaussians. also to reduce ihe effect of small fluctuations in the lelcscopc guidance. F. BUSSOLETTI: What are the peak intensities and the corresponding brightness temperatures in C. ANDRIESSE: Wh?t :=WHM do you get for Sgr A and Sgr B2? both Gaussian intensity distributions fitted to the pro file of Sgr A? R.E. JENNINGS: The separated peak fluxes for Sgr A and Sgr B2 are 45 and 34xlO"IOW m"2 R.E. JENNINGS: After corrciion for our beam (40 - 350 fim. beam 5.6' HPBW). Simple analysis gives size we get values of 7' and 29' for the separated and the effective (black body) temperatures as 22 and background components, respectively. 26 K, respectively -.NB. latter too close to assumed colour temp. - further investigation required). G. NEUGEBAUER: Do you believe that the two gaussians represent physically different regions? E. BUSSOLETTI: You said that the spectrum of Would a 1/r law fit? W5I that you presented has been taken a' a resolu- 1 A M.VAKI 7 I T AL lion of 3- cni"1 On the cnniran. the points ihai you represented by a lUiitimuws curve. In averaging the showstvm to have a lusher resolution byahout a hall". spectra ttow several intcttciugrams we loiind it con How is il possible'' venient io take an average at 10 cm"1 intervals. This spacing is arbritrary but is sufficient to present [lie R.E JENNINGS. The computed spectrum ob data which is at a resolution of 32 cm"' tained using a Michelson Interferometer n. often 1 MGU-RESOLimON MAPS OF H11 REGIONS AT FAR-INFRARED WAVELENGTHS G.G fniiu. DE Kfcinimnn. R.W. Nnyes. EX Wright. &. M. ZeiJik II Center for Astrophysics. Harvard College Observatory and Smithsonian Astropbysicat Observatory Cambridge, Mass.. USA F.J. Low Lunar and Planetary- Laboratory. University of Arizona. Tucson. USA ABSTRACT The first ttK<.*s$fui ihplii ot a haiïuon-borne 1-m ioimn of )'. Paitial maps uT these regions were made telescope lor fat-infiated (> 40ym) astronomy with a resolution of 0.5'. These sources were resolved itcumd tm 4 Fehiuary î'>74 iUT>. fmm Palestine. mm several components, some of which were pre 1 cxas During 6 h ai Ileal altitude, the gyro-stabilised viously unknown. Observations of Mars were used for telescope napped the intensity of far-mfored radi- calibration. iition fttim the H H regions On A ami W,"* with a rcsô- 1. INTRODUCTION On 4 Fehiuary i'>?4 lUT). the Harvard College On A and W3 were mapped with a resolution of I ', Observatory, the Smiîhsuman Astrophysics! Obser- and partial maps of these regions were made with a vaiory. and the University of Arizona launched a resolution ot 0.5*. Absolute positions were deter lO^cm-aperture balloon-horne telescope from Pales mined to approximately 0.5'. The results of these tine, Texas, to map HI! regions at far-infrared wave observations are the highest resolution maps ever lengths t> 40 *mi>. During the flighi. the 11II regions made of Ori A and W? at far-infrared wavelengths. 2. INSTRUMENTATION The telescope optical system shown in Figure I optical fight onto an N-slit mask at a second focal consists of 3 conventional Cassegrain arrangement plane. Light passing through die mask is then focused with an (12 solid aluminum-alloy primary rWrror, onto a photorrraltipliet tube. A «movable eyepiece, spherically figured, that feeds a pyrex secondary to mounted in the focal plane behind the second beam produce an f/13.8 beam it the focal plane. Three splitter, aids in optical alignment. The Cassegrain mir focal planes ate provided. The infrared beam is reflec ror is mounted to a solenoid-djt.en chopper mecha ted by a drchroic beam splitter and focused onto the nism that causes the mirror to ascdlate in the azi bolometers. A second beam splitter directs half the muths! direction in a square wave motion of 20 Hz :fc hipirr 1 Tclfw yv optical syitem. trequencv The wpjration ul the Iwu hearm is 5..'' The chopper mechanism ii mounted un a cummand- jhlc locus drive. Tlie infrared detection system consists ol an array S.l in high and .1.4 m x 2.1> m wide, and weighs ap- gyroscope system mounted on the telescope tube. pioxiinaicly IRIX) kg. Mapping of an infrared source is performed m the Positioning of I he telescope optical line ot sight is inertial mode either hy automated raster scans or by atcomplishcd m Iwn modes first, an acquisition manual-command a/imuth and elevation scans. mode, deietmincd with respect tu the horizontal f-urther details on the construction and operation Liimpniieiii o( the (-arth's magnetic field in arimuih ol the telescope are given in papers hy Fazio et al. and with icspecl to the local vertical in elevation, and (W74|. Ha«n [!<»74|. and Hazen. (oyle. 4 second, .m inertia! mode, deiernuned hy a two-axis Diamond |1'»74|. 3. OBSERVATIONS Aller a very slow ascent, the balloon reached the set signal of the Tout detectors was about one-halt of float altitude ol 2Rkm and remained in telemetry the signal from Mars. tange for b h. Dining this time, three H 11 legions. For detector (A), the angular resolution in the NGC 753R. On A. and W3. were scanned as well as a/imuthai direction was measured to be I 25 the planet Mats. ( FWHM). Two tastei nuns were attempted on N(i(" 753H at The ephemens position of Mars was used to check the beginning ol the flighi: hnwevei. later analysts of the alignment of the infrared beam with two the i men latum data shows iltal this object was not star-sensing systems, a camera attached to the tele scanned scope with a 15° field of view and the N-sln photo Mars was scanned several tunes to determine the meter with a 20' field of view. The positions deter .ietectot respoiisiviiy. angular resolution, and the mined from these systems ate accurate to 0.5' ( I a). alignment of the infrared and optical systems. Assum About 2.5 h was spent observing the Orion Nebu ing Mars has a bnghtness tempetatute of 235 K (Arm- la region, and the map shown in Figure 4 was con sttong. Harper. & Low. 1972) in our wavelength structed from this data. The contours on the map hand, and an ephemens se mi diameter of 4.0O", we show only the bright parts of the Orion source; cover obtain a flux of 1.1 x Iff11 W m"2 Hz"'. age inside the figure is complete to the indicated flux Foi Planck black-body functions, the flux-correc- tmn factor (or effective filter bandwidth) is given by J00R(i>)B(J'.Trdi> A^(T> = R(fo)B(i-0.T) 1 -80 cm" n0.5e0 where R(v) is the instrumenlal response, Bl>, T) is the spectral emiltance of a black-body of temperature T, and /^RWBfv.-OMlV /„ R(e)B(i\T)di/ S^SÏ™»* filV RIGHT ASCENSION (IMOCO is the efTective wave number. Over the temperature interval 70 le\el. The lowest vitmoui is SO units the Nr-'K Ihc 3O0u 00* KV ICV highest peak flux is at rhc position ot ihc Klcinmann- Low Nebula (KL). the measuied pusitinn agtees in the «known position in u-nhin 1 n The appaieni flux f \ ORION ;| : l 1 / \ NEBULA is I S \ 1(T W m" H/' JI o >yin. 'hi si/e, as determined from lite peak tlu\ observed with the 05 > 15 The second peak neai i.': On is much tainici and more extended Thete ate several possible souices oi excitation tor this, peak (*:A On. liee-ficc coimii- uum peak observed tu Uebster & Alu-iuWt |l070|. or the bright nm of the optical nebula. The extended infrared emission sprees with the position angle and si/e of the source seen in the 11 cm - apertute syn thesis map of Webster & Altenhoff 11 «70) The radio map shows further bright peaks near the Trapezium stars, but at t*9 fim these are masked by the Klein- mann-Low Nebula. The integrated flux of ihe extend ed source u uncertain, bul il is quite large 4<+3. 11 x l(Jai Wm1 Hi'. The flux distributions of the sources in the Orion Nebula region are shown in Figure 5. The data are a summary of Ihe «suits of Ney & Allen ]1969] at 11.6 and 20 pm: Rieke. Low & Kleinmann [1973| at 10.5 and 21pm; Lemke. Low & Thurn (1974, at 21 frm; Kleinmann and Low [1967] at 22 um: Low. Rieke. & Armstrong [1973J at 34 um; Fazio et ai. [1974] at 69urn; Harper [1974] at 91 um:Hoffman. Frederick, & Emery [1971] at 100pm; Low & Aumajin {1970] at SO - 300 mn: Emerson. Jennings. & Moorwood |1973] ai 40 - 350 nm; Harper et al. |1972] at 350 urn; Harvey «I at. |1974) at I mm: 105 HO US 120 G5 "30 135 110 Low (1971] ai I mm: and Ade. Clegg, & Rather log *(H;; [1974] at 1.4 mm. The KL source is well represented by a 70 K Figure 5. Flux distribution of sources in the region black-body spectrum from 30 - 90 urn. For a size of of the Orion Xebuta. 35", the lumuioshy is 7 x 10* LQ. The total flux of the Orion Nebula is also shown. It is three to five limes larger than the KL source at 70 - 90/im. and from 8 On, observed by the Celcscope experiment about ten times larger than the KL source at 20 pm [Davis. Deutschmann, and Haramundanis, 1973} on | Lemke, Low, & Thum, 1974J. Thus the tola! lumi OAO-2, is quite high (M0"a W/ma for XF^ at nosity is approximately 3.5 x 10s L©, or 4.5 x 1400 À), so with a 1- or 2-mag correction for inter 10"BW/ma. The colour temperature from 20 to stellar extinction, one has the required power. 70 pm is about 100 K (Harper & Low, 1971; Lemke, The nebula M43 was detected with a peak flux of Low & Thum, 1974; Fazio et al.. 1974]. For this 3 x 10"2i W m"1 Hz"1. The source was extended (3 temperature, the optical depth of the dust at Ihe + I'f and located on a wing or the cmissto,) from southeast peak (near B* On) is 0.01 at 70 um. The M42, so its total flux is very uncertain, but the data corresponding ultraviolet extinction optical depth is are consistent with the hypothesis that the ratio of about 10. For grains with a large albedo (A), the fluxes of M43 to M42 is the same at 70 urn as it is at ultraviolet radiation will reach a characteristic optical 2 cm [Schraml & Mezger, 1969]. depth of l/(l-A)^ for isotropic scattering, and The molecular cloud OMC-2, observed by Gatley 1/(1-A) for forward scattering. Thus, it is possible et al. [1974) in the wavelength interval 1.6 - 20 um, that the extended infrared emission in the Orion and by B. Warner [private communication, 1974] at Nebula comes from dust behind the nebula, heated 3 J 1 J mm, shows a flux of 3 x Iff* W m" Hz" at by stellar and ultraviolet photons. The ultraviolet flux 69 um and is not noticeably extended (less than 1.5'}. HICiH-KISOt t HON MAPS ()!• H 11 KK.IONS IN 1 AH IK W3(A) Figure 6 Map <>J h'J rcgim. at an effet wavelength •// Wi pm. Omimm art UK-K •>}• f, x 10 '• h>n 2 Hz ' in beam, tir .1 < 10 ' 7 hm : //. ' » Tahle I. Summon <•/ f/ic fuMtt-ci observed in the region •>} WJat an effective wavelength off)'/ fun SOURCE C Peak llux Total flux Source Iff" Wrrf '»,- Si/e Iff" V, m~! 11/ J 6x 10" W3 (OH) U.Î(A) <6x 10 1.1' "..KOMI 7x 10J C \0> :.4' :x IO1 11 600 0.6' 600 Our measured position of the peak is aU''50) = brightness. If source C is optically thick, its brightness Sixmos, «( 1950) = - 5° 113'. Its spectrum is also temperature is 17 K. while for an optical depth of given in Figure 5. Iff1, the brightness temperature would be 45 K. W3 was observed for 35 min at the end of the Observations of the carbon monoxide line as well as flight. Positions are much more uncertain here, by 2um and 300 pm infrared observations will show approximately a factor of 4. than in the Orion Nebula whether the source is similar lo OMC-2. Source D was region because the end of the star-field camera film 0.1 times as bright as W3{A) in the small detector was fogged during recovery, and there were no bright beam, but only 0.02 times as Kright in the larger stars in the fl-slit photometer. A preliminary map of detector beams, so the source is quite small (—0.6*). ihis region at an effective wavelength of 69 pm is Only 25^ of the area mapped was scanned by the shown in Figure 6. The two brightest sources ob small beam, so we cannot say much about the fine served agree within 2' with the absolute positions of scale structure, other than that it exists. The results W3( A) and W3IOH), so the identifications are certain. of the VV3 observations are summarised in Table 1. The relative pusilions of the sources in the map of W3 The H II region G 133.8 + 1.4 was not detected, are reasonably good. Wc see thai the primary source, but we did not make many scans through the centre W3(A(, is extended to -1.9' FWHM, while the of this source. The closest scans, located 2' above and W3(OH) source is small |< I '). Two new sources were below the centre, are within the radio source seen by observed. Source C (~2.4' in size) has low surface Schraml & Mezger 119691. ^4 Ci, I A7.I0 IT AL 4. CONCLUSIONS Hsgh-resoisiiton. tucjî-sen«tmty. faritiftaccd eh- W.ï into several voraponems Sk»me of these compo- scrvatiom with a 102 cm balk>uri-bome telescope ncnts were previously unknown. have resolved the hnght infrared sources On A ami 5. ACKNOWLEDGEMENTS The paylca4 was designed and constructed by the well as the tiata-piocessmg equipment at the gtnand Solar Sjielliie Inpneenng Group. Harvatd Colleger station Without iheii assistance, this flight would Observatory. have been impossible. The National Scienutlc Balloon Facility was res Tim work was supported m pari by funds from ponsible for the bunch. Hacking, and recovery of the: the National Aeronautics and Space Administration experiment and contributed' iheonhocrd telemetry a*i undri pant NCR 22-007070 to Harvard University. REFERENCES 1. Ade, P.A R.. Clegg. RE. & Rather. J DC .^i/r^ Sato. T. &. Litvak. MM.. AUmphys. J. {Lett.) /*.« / iUlLf 189. L23(1974) I«9.L87Bome Research, (Lett.) 149, LM1967). NASA Ames Research Center, Cal., in press. 16. Lemke, D-. Low. FJ. &Thum, C.Astmn. Astro 6. Fazio, G.G.. Kkinmans. D.E.. Noyes, R.W., phys. , in press. Wright. E.L, Zeilik II, M. & Low. FJ.. Astro- 17. Low, FJ., in Dark Nebulae, Gobules and Proto- phys, J. {Lett. I, m press. stan (E4. B.T. Lynds),Univ. Arizona Press, 197!. 7. Gatley. I., BecWin, fc.-.. Maithews, K-, Neuge- p. 115. bauer, G., Pension. M.V. & ScovOle. N.. Astro- 18. Low, FJ. & Aumann, H.H., Asiraphys. J. (Lett.) pAvs./. fX*K./, 191, L121, (1974). 162, L79(1970). 8. Harper, D.A.. Preprint No. 123. Depi. of Astro 19. Low. FJ., Ridte, G.H. * Armstrong, K.R.. Astro- nomy and Astrophysics, University of Chicago, phyy J. (Un.) 183. L105 (1973). 1974,58 pp. ,20. Ney, E.P. & Allen, D.A., Astrophys. J. (Lett.) 9. Harper, D.A., Jr. &. Low, FJ., Astrophys. J. lSS,L193(19o9). 21. Riefce, G.H., Low, FJ, A Kieinroann, D.E^Astro- 10. Harper. DA.. .fr„ Low, F J., Rieke, G.R & Asm- phyi J, (Lett.) 186, L7 (Î973). strong, K.R., Astrophys. J. (Lett.) 177, L21 22. Schraml, J. & Mezgcr. P.G., Astrophys. J. 156, (1972). 269(1969). 11. Harvey, PJ*.. Galky, I, Werner, M.W.. Elias. 23. Webstei, WJ., Jr. A Altenhoff, WJ.. Astrophys. J.H_ Evans II. NJ., Zockennann, B.. Morns, G„ Lett, 5,233(1970). HIUl-RtSOl l.TION MAI'S OF It tl KI-UONS IN 1-AR IK no DISCUSSION B.BAUCK I'd like to point out thai the 70 um I-..L. WRIGHT Yes. 1 have assigned 5x10* fu ,,] map is most closely correlated with the molecular the observed 2x I (J* fu at K L to the extended source distribution as defined hy ihe ' *CO distribution. V..e The Ney-Allen source itself is much fainter than this. tine of -.igJn to 01 \ is tangential to the interface hecause the hot dust near I lie Trapezium has a very hot ween the ionised nebula and neutral gas, and here low optical depth at 70 um. (as you have predicted) far infrared emission could be expected because the dust is being healed by th H.L WRIGHT The IR sue of I."' IFWHM) is larger than the size given by Schnml and Mezgei. E.L. WRIGHT: My factor of 103 is very crude. I xl .3'. The tail to the soutli and west at 2 cm is not Assuming a 1/A dependence from 70 um to 2.2 um present but a slight asymmetry is seen in ihe south gives I0,-Ï.K to Vgives 10' and V to UV gives I0"s. west. If the UV extinction is low a high albedo is not re quired. E.L. BBCKL1N: Did you correct the peak signal from the K-L nebula for the Ney-Allen source? W i IN THE NEAR INFRARED M. Beetz. H. Elsasser & R. Weinberger MavPlanck-Jnstilut fur Astronomie. Heidelberg. Cermny Ruin photographs taken with an image lube camera (.Sltalhi>de| in the R- and I- lange(0.70and O.'^uml at the 72 cm reflector of the Heidelberg oh&ervalory. we hjve derived new information on WA(A). The limiting magnitudes wiiii an exposure time uf I h were 1 = 14.5 and R = 17. The photo graphs (t-'ig. ii show at the position uf W 3(A) an elliptical nebulosity of approximate size 5" to 8", identical to the infrared source 1RS I of Wynn- Williams. Bcckhn & Neugebaucr |1972]. Nea *-.y are twn sources nf stellar appearance. The more easterly of these coincides with ! RS 2 which Wynn-Wjlliams et al. observed as an unrcsolvable source, and which they believed to be a heavily obscured early-type star. Our photographs present evidence for the stellar na ture of IRS2. The mure westerly object of stellar appearance (1RS 2a) is identical to a 18.1m star on the red PS5 print of this region whereas it is absent on the blue PSS print. The photometric results confirm the steep reduc Figure I. Photograph of W3/A) m the I-range tion in energy distribution of 1RS 1 towards shoner 10.92ftm by image tube camera Inorth wavelengths and allow an independent determination at lop, east to left). of (he extinction in front of 1RS I. In full agreement with Wynn-Williams et al., we find an obscuration m A v = 15 . The energy distributions of the two stel lar sources arc well represented by a curve which fol compact 11 M region W3(A). Both are located close lows for a 3. 1 kpc distant 05 V star obscured by to the geometric centre of W 3(A). m interstellar extinction of Av - 14 . Thus both 1RS 2a Details will be published in Astronomy S Astro and 1RS 2 seem to be sources of ionisation for the physics in 1974. REFERENCES 1. Wynn-Williams. C.G., tJccklin. E.E. &. Neugebauer, G..M-VRAS 160. 1(1972). OBSERVATIONS OF W.l IN THt 40-350 jjm BAN» I hurnkv R E Jennings & A.F.M Mmirwuod* UimersiK College. Uindiin. LK Tlif regiu/i i't W.l *a\ i.SuTM'd m the wavelene.1h Hie map lias twen prmtuced »!lli an t*lleLi!.i- Iwnd <>t W^dpm. usine ilie U'1. fclliiiin-B»ine beam MA- ..i 5' in KA a ml f..5' i" dcJinati'm. Il.e 7 : svsieni, in Mav l" .' The lipure \hi»wn is tin* result L.intout micrva: i% I 0 \ Kl ' " tt m v.nti [lus heait'. ing map obtained aller deLonvolulinn i>l ili,. stpnal-. Il s.lu>ws the three wniKe* ol tt.ï rrpi.neil bv Sdir.in:l wiih nui hcain iL-srxniso. Jet ci mined l>\ ubscrvini: A MC/KI*I |l')l.'»| ai I5C.H/. the \lï n.iiimuuni Jupltei. usmp a f ouricr (unslnrfii leJinuiuc «rtirce- I CONTINUUM RIGHT ASCENSK)h|l930l • No» \ulh Aitrniuimy Divisum, l:ur«itean Spate RL". Oisarisatinn. Si» centre, and Us a»oaated Hll irpii'îi. lil.v'" •• 1 The llnves I'm these liner main s and the noilliem icntinuuui component tVLvif» in a papei ..Iscwhcie in llit* edinps |liiiiiiss, Ji'TuiinpsA Mooiwooil. 1"?-1| Kvtending ft it in ihe hodi ol the iiuin inmponent Tlie peak IR lint; positions are m agicenicni nil IN a lone emission Jim whuli could be a krarili com Hie peak ndio continuum punitions measured b ponent ol lat-mtured emission fui this region winch Sell u ml Ai Me/gei to wtltnn JIOM frottai .iciuiaci we haic failed lo icsoke Schraml. J & Me?pei. P.C.. Ap .1. 156. 2t# Run»*., l., Jennings. R.I.. & Moomond, A.I-.M., Tliis Symposium. 350 Mm MAPPING OBSERVATIONS OF M42 AND Sgr B2 M. Simon Department of Karth and Space Sciences. State University of New York, USA ABSTRACT" Wc have earned mil 350 jim mapping grains and conditions within the molecular cloud. The oliscrvaiions with 5(>" resolution of the suhmilhmelic high optical depth implies that rtlOOuml - 1 and source associated with M 42. The source peaks at I he thai Tl20jim| » 1. This implies that the objects in position of the Kleimann-Low infrared source, and its the infrared cluste; discovered in this region by Rieke inli> -siiy distribution is similar to that of the molecular REFERENCES I. Andriesse, CD. & Olthoff. H.. Astron. & Aitm- Ricke. G.H.. Low, F.J. & Kleinmann. D.E.. Ap. J. phys. 27.319(1973). (Utt.) 186, L7 (1973). 1. Gezari. D.Y.. Joyce, R.R. & Simon, M.. Ap. J. Wynn-Williams, C.G. & Becklin, E.E..PASP86, 5 (Lett.) 179, L67( 1973). (1974). • The Orion observations aie scheduled for pubticalion: Gezari, D.Y., Joyce, R.R.. Rtghini. G. & Simon. M., Ap. J. fLott) 191. LOO (1974). Wc therefore only summarise that work here. A manuscript on the Sgr B2 observations is in preparation. 92 M. SIMON DISCUSSION MARIE-CLAIRE LORTI-T: Concerning the M SIMON: The contour levels were drawn at the H: CO cloua in Orion. I would like to ask whether the levels 2. 4. 6 and 8 kiloflux units. The outer contour southern extension was detected at 3Mym or at level at 2 kfu is thi ', at a level a link bcttei tlian one shorter wavelengths'* o. and as noted, is therefore uncertain. M. SIMON: It does not appear on either the E.K. BECK UN. Is there any theoretical reason to ?50 (im or I mm maps to the present flux levels. assume av1 law for the opacity of grains'' If a >' law is assumed. Urge optica) depths al lO^un and 2ùfim E. BL!SSOLETTl: The scan through Jupiter are not required. appeared quite noisy. What is the S/N ratio for Orion and Sgr B2 and can you say something about the at C. ANDR1ESSE: If there were a weaker power mospheric window at 350 jim? law, say v' '*, one would find that the Kramers+aunig sum rule would give an unbounded value for the reac M. SIMON: Our peak flux on Orion is (8.8 tivity in the grains. Since physical causality requires + 1.6txl(TJ> W^n1 Hz using a 2.2 m telescorx and thai the reactivity be a finite value, one expects a f2 56" beam. For Sgr B2 it is (40 + 3|xl0~13 W/m1 Hz. power law (or a stronger one). This only applies for The noise in the Jupiter scan was due to opacity fluc very low frequencies and I don't know the frequency tuations: it was a bad night. at which deviations become apparent. This may be different for different materials. D. LEMKE: What was the S/N at the centre of the Orion map and for the outer contours, how many 93 I mm OBSERVATIONS OF H II REGIONS P.E. Oca * P-A.R. Ade Queen Mary Colkgc, University of London I. INTRODUCTION Broadband observations of five IIII regions have region, wide passbands are generally used for these been mad* |Adc. Clegg & Rather. 197.Ï, l«74;Clegg. observations, as will be shown below, this presents Ade A Rowan-Robinson. 19741 al Kill Peak, Arizona problems both in calibration and in determination of using the 11 m National Radio Astronomy Observa- the mean wavelength of observation. In particular, lory* (NRAOI telescope and (he NRAO I mm receiv atmospheric conditions have a considerable effect on er. The properties uf the telescope and receiver at observations around 350jim. Asaresultof takingihese I mm aie described in previous papers [Ade. Raiher effects into account, we believe that the subrnilli- & Clegg. 1974: Raiher. Ulich & Ade. 1974; Ade. meire spectral index of the regions we have observed Ocgg & Rather. 1974). Fluxes were calibrated is about 3. against planets | Rather et al., 1974], assumed to have A very simple dust emission model for the sources spectral indices of 2. We are here concerned with is considered. From estimate* of the total flux of the using these results, in coi.;unclion with measurements source, the spectral index and a monochromatic flux, made nominally at 350ym by Harper. Low, Rieke & a temperature can be estimated for the dust. Using Armstrong |I97?| and by Riekc. Harper. Low & this enables an estimate to be nude of the total d -,i Armstrong [ 1973), to establish a mean spectral index mass which, for a source of spectral index 3, is inde in the submilhmetre region. Because of the relatively pendent of the grain size. weak flux reaching the detector in the submillimetre 2. DETERMINATION OF SPECTRAL INDEX Suppose tl.ai the spectrum of a source is Sfr), so the atmosphere, Alters placed in the system, and the that the power P received from the source at the spectral sensitivity of the detector. In the case of the detector is given by 1 mm observations, the 36 ft telescope provides a strong high-frequency cut-off due to surface imper P = Çswmto (1) fections [Ruze, 1966]. The 350/on observations were made using the 88 inch telescope at Manna Kea where f(e) is the overall filtering of the system. In the Observatory, Hawaii and the NASA 60 inch telescope millimetre and subrrnllimetre region, thji filtering is at the Cataliiu Observing Station. Diffraction affords the result of the combined effects of the telescope, Some degree of high-filtering but this is less than is often supposed. Figure 1 shows the total energy received, as » function of wavelength, within the Airy The National Radio Astronomy Observatory is operated disc for a wavelength of 350 um; it wfll be seen that by Associated Univcnib» Inc., under contract with the the efficiency falls off relatively slowly with increas National Science Foundation. ing wavelength. I 111,1. S f \ K M>l IrngtU. witlim an m\ .•/ Juimrtir ,;pm! i.• the ttr*r dark ring ••/ the Am ,in, at L Figure?. Fractional transmission oj the atmosphere, as a function of wtf numher for prcdpirahlc waier-vapour ctmcentrations of 0.4J. 0. VS. 2.00. 4.SO. and V SO mm Figure S. Atmospherically rransmilted energy as a function of vxvelcngth from a thermal source for the water mpour concentrations of Figure 2. m (IBM 1H AI HAS (Il II H Kir.IOSS l.lk'il U\ wak-l wlierc hm.lhm IfiiKlh' l...l!i ..•p.' ..n.l .•• >v|ini . et le , WJVl' Il lengths hiA.mJ I mm (-iptiu- J -.1, tuns mission spiMrum "I the .il nu •sphere Im via ter vapum i alune. Im v.ii!i'ui vsatei vjj'i'iii LimLfriu;i(i.>iis, ami I ipiue ; ihe traiiMiiilled enemy li.un ,i M>UM' "I Njifili.il iinle\ ' Hheiiriai sonne i h ian hc s^en tu un I .pue ù tti.it unless si roup low ]ieijiK-n<.> lilk'rmji i* f applied -uiiMilfuhlf IniiM-uaselentîtli energy will j ihe ir..ipr"i.al ->l i>n fui n - ' ihe mean wase- .onttibute ii' rinniiiul t^O^m tiieaMiienietils (here k ijiih i\ omsn'erahly lunger than ;i;i);jm i"t all i\ m. lelrienie tu any \IR)I liîu-nnj;. other ilia» the « 1er sapuui tonLcniral].mi .littiailion rtkii. m rlie papeis i>t Marper ei al ami ("1 a planet wilh spectral index ;. trie measured Kieke «M al I-. temperature it loi a smirce ul spcclral index. 11. u I'liiwn. since i': is known tor given atmospheric mri- liitmns. hquation _* then enables us to determine S*i' i tut the source at some unknown mean fre su = S. n quency vn To obtain i'n it is necessary to obtain n by sUieie i-„ is J normalising Irequcncy and S,, is a observations with a different littering function I'(t'l. sianl from hi|iiaimn- <11 ami l.l. tmm hquation (2i , Sl"n> V- -•""n' "n - ^""""*—•«^^^ Wn longwava cutoff (3 Omr n PWV.J S 2 0 ^^^^^^S= Longwav» cutoff - Top 3-Dmir PW.W Midoto 20mrr PWV Bottom 1-Omti PW* 1 1 1 1 1 1 1 SPECTRAL INCSX. Figure 4. effective wavelength as a function of spectral int. "x for rV nominal 1 mm filtering functions. P.I. CLUX; 4 PAR AI)i where f„ is live- mean frequency obtained by using f"(i'l. From a plot of n logi^'/V,, against u we can iihixin from any two flux measurements SfV„)ani} Sfvn) the value of n, and hence the values ol i' n and »'n Although the mean frequency, as defined above, is necessary for ohiaimng the spectral indices, a mure appropriate measure of the frequency at which the observations are made is the effective frequency i'n. given by wliere B^v) is the energy received at frequency v from a source of spectral index n. Figures 4 and 5 give An (= c/£jjf as a function of n for the J mm and 350jim observations, respectively. All fluxes have been represented at ihe effective frequency v^ by SPECTRAL INDEX I St^i = &nl!>Jfs&n) Fïgure5. Effective wavelength a% a function of spectral index for the nominal 350 um filtering function. (Urns wavelength cut off is that produced by llu- Ain-function alone). J.1HII • AW- «SOU • I 5*MJ ""' IIMI I4JU 11X1 « 17(1 I4K0 .(SO 7iM» 11* :HSO 11(1 MB KUDO .1011 I mm OhSI-RVATtONSOI 11 II «I (.IONS i. OBSERVATIONS Tabic | give* the ! mm thine* a.id the results of Table 2 shows the mean wavelengths ana speural Harper et al. and Riekc ct al.. together with ihc beam indices, deduced in ihe wa> described above In vie» sues, lor the sources M42. DR: 1. W4'». W51 and Sap tit the errors in the flux measurements and ihe unLer H2. In the fourth column ol Table I we have correc I am I les in the atmosphern. conditions jl ihe time ot ted the .^SOpm fluxes lo allow (or ihe mean wave ihc observations, no attempt has been made to assign length «I observa I ion of the calibrating planet being errors to these indices However, il will be seen thai closer to 400;iin than to .150 pm. The 1 mm fluxes the set ol indices obtained clusters around the value from M42 and DRJ1 have also been corrected tor i. we adopt ihts value pruvisionalh as representing extiapolatcd Irec-trce emission. We have not made the mean spectral index tot these sources in the iuh- similar corrections tor the other sources because ni millimetre region uncertainties ot the radio flux within our beam Effective Effective Source wavelength in wavelength in Spectral index 14 mm region 400 tim region Orion IRB 1.28 365 3 M42 (total flux from 1.18 350 4.4 .V diameter source) OR 21 lib 350 >4 DR 21 Norlh 1.18 355 3.7 W49 1.30 370 2.8 W5I 1.20 360 3.4 SagB2 1.22 360 3.2 All values assume 2.0 mm PWV for 1.4 mm observalions and 0.5 mm PWV for 400 fim observations. 4. SIMPLE DUST MODEL In order lo obtain a crude estimate of the masses a Q\ = Q0(a/X) ;a«X of dust involved in giving rise lo the observed sub- millimetre fluxes, we make the following assump where Q0 and a are constants. tions: (i) The source consists of a spherically symmetnc With these assumptions, it is easy to show that cloud of dust particles of radius 'a' at a uniform the monochromatic flux density S(i>) in the Rayleigh- temperature T. Jcans region is given by (ii) The source is optically thin over all frequencies at which appreciable infrared energy is emitted. S|r)ai'î+a (iii)Thc emission efficiency of grains in the infrared is given by and thai the relation between the total infrared flux o,«, r I < i H.I. IIMK \nt 1 emitted f*\ the vuiir nu*. Slrt f p*en H temper at me ol the regitin van be obtained tintn t-.quation (5) il the total mimed flux i\ known Untonunately. the beam width used in obtaining esti a mates ol the tola! flax (ifatpet A low. |<»7i| is - -'(.i • :>' î » rL » fS* i Si t - bl - X aie, and there I ore contains much more (aillatum (in an extended sourc> than oui I* 31c beam. How and thai tin- total mass. M oi the emitting grams i"s• ever, tor (*= I. Equation (51 indicates that I wanes fiSU*il H only as IF/tSffll' * and therciore rough estimates of the trmpetature can he obtained fn-m a v«y uncer tain knowledge of Mm tatto. these tempciaiure* ate shown in Table 1. Ii can he seen that til these arc uf - tUQK. and we lute used this value 'n Equation aiicre Jj t> the densiH of the grain material and ï>t'ts thi. topethct with the source distance; given by the distance ••! the somce Note thai, il we assumn?e Reilenstein et a! |1**70). to estimate the dust mas- thai the I mm measurements fall in the Rayieifh!*>-• scv These ate also given m Table i. Of course, it is Jeans tegion nt the spectrum tut ihe Just cloud, aJ nut suggested that these figures ate tellable estimates tpecnal mdc\ o! - implies that a » 3. Substitution "v\' oi the dust content of the sources. They show, Uow- this value oi a in Equation (to show* that an estimat'te ever, that the millimetre fluxes can be interpreted as oi she dtisi mass can he obtained independently o°f emisijon itom reasonable amounts of tifttcalH thtn knowledge of the size uf the grain. An estimate of thhe dusi with an ctmssivity a X"'. 5. CONCLUSION We have shown thai the atmosphere plays ain thermal emission from optically thin dust, the absorp- important fuie m determining the mean wavelengtth fion coefftcieM of the dust grams should vary as X" ' of submillimetre observations. Analysis of millimetrre (cf Fig. 8. Ade et al., 19711. The masses of dust and submillimeite fluxes suggests a spectral index oaf required to produce the millimetre emission are ~ 3 for several H il regions, if this is interpreted as moderate. 6. ACKNOWLEDGEMENT We are indebted to Mr. MJ. Pugh for allowing us publication, access to his water-vapour absorption data prior to 1. Ade. P.A.R.. Bastm. J.A-. Marsion. A.C.. Pandya. 6. Harper. DA. & lxnr,fJ.tAp.J. 165. LOf. 1971). SJ. & Puptett, E., P;oc- Second Lunar Science 7. Harper. D-A-. Low. FJ.. Râke, G.H & Arm Conference, MIT Press, Vol. 3. 2203, 1971. strong. K.R.,Ap. J. 177, L:i (1972). 2- Ade, P.A.R, Clegg, P.E. A Rather, J.D.G., unpub- 8. Rather. J.D.G., Ulich. B.L- & Ade. P.A.R-,/amu Ëshed. tin press). 1974. 3. Ade, PAR.. Clegg. P.E. & Racher, J.D.G.Âp. J. 9. Reifemtetn, E.C., Wilson, T.L. Burke. B.F.. I89.L23(1974,. Mezger. P.G. & Altenhoff. VI.} Astro». & Astro- 1- Ade, P.A.R-. Rather, J.D.G. *• Clegg. P.E. Ap. J. pAn4.357(1970). IS7,389 0974). 10. Riekc, G.H., Hatper. D.A., Low. FJ. A. Arm 5. Clegg. P.E, Ade, P.A.R. & Rowan-Robinson. M.. strong. K.Rjlp.J. 183,67(1973). Nature 249, 530(1974). t mm OHSI KV A 1ÏONS (II- li II Rl (ilONS DISCUSSION M SIMON I won]J urge gréai caution in at- I F. Ifl.CKUN Did >ou din-eel tor the energy icmptinK in detinr .\C|-f fur the various submillunetre outside vim» M" beam' observations since H depends MI much >>n Ihe particu lar msinimentation, For example, with our instru P I: <"l KG(i The 1 mm beam ot the ! I m mentation optimised for .l^Opm work, and with NRAO dish consists of a 65" gausstan •.urmountmg a «tilth transparency at 350pm of - MY'-, a Rayleigh broad pedestal of - 6' FWHP We were beam switch Jeans optically thick source gives us — (>5'^ tlux ing over 130" and we assumed thai this switching through the 350pm window and ZCfi through the effectively eliminated energy within the pedestal A 450 pm window The 350 pm ratio is obviously lar switched beam scan across Jupiter confirms rhh tiieatet for a sleeper spectrum. K W MICHF.L How good are the derivations „! P.I- CLbCCi' Ot course, ideally, observations Ihe total dust mass from emission measurements with should be made with narrow-band filters but ihe out more detailed information on the si/e distribu available energy usually dictates the filtering. It is tion'' nevertheless important In attempt lo determine the mean wavelength. P fc. ("LLC;0: The model is crude. However, pro A transmission of W.'. in ihe 350 pm corresponds vided that, for all wavelengths at which appreciable io I mm of precipttable water vapour !-.ven consider emission takes place, the source is optically thin and ing transmission through the 350pm and 450pm the particles are much smaller than the wavelength, windows atone, uur calculations for this amount uf the conclusion based on the model is independent of water vapour predict nOV; energy in the 350 pm win size distribution. dow and 40" I m the 450 pm window for a Raylcigh- Jeans source. The bases nf our calculations are con S. POTTASCH: I missed the reason you gave for firmed by solar emission spectra using a polarising thinking that there is a constant spectral index Michclson interferometer. between these two frequencies. For sources with higher indices, the proportion of energy in (he 350 pm window will indeed be greater. P.E. CLEGG: 1 assume that then* is a constant However, it is essential to remember that the calibra spectral index, because with two points I am unable tion source bas a spectral index of - 2. to fit anything else. 1.3. General Discussion 101 CJFNERAL DISCUSSION Chairman f) l.emke I) I I MM II has been suRpesir.t llul hetore reported tr.-m This pmil|..r. A lull .iis^uwoti is *-c:r.if dosing tins ««urn *c MXIIJ IUK a short ^encrai dis prepared ii.r publication h\ Knersun furnis* A cussion in LJSO .IM\NK|> lus hci-n confused h\ i!.r Jcnniii/* papers we haie hejid vu tai I would like. therefore. to mute an> questions LO: .ruling these- papers "i ( ANUHII-SSt While diMijtsing the inirared any other comments tlut ; ou would like to make einssion tmni H M répons in terms of dust, we sit'>ulil not forget the possibility ihat al leait pa:i ol H HAHINL. Une ol ihr puipiise» of ilm nieetiiijz ihc emission is due l>> forbidden transitons in mni ! ii to establish correlations and this is J lair slalernero, would like In ask fH Potlasch to crnmenl on ilm cxi\pt lhal otic lias l.i speul> exadls whai 0. LEMKE: Does Dr. Greenberg bave any com V. PETROSIAN: In dusty H II regions with dust ment on that'' optical depths'of the order of unity, only a small fraction (~ 10T?) of the ionising radiation is absorbed J. MAYO GRtENBERG: As Mark Twain said. 'I by the gas, and only a fraction of this will be radiated am very happy to be able not lo answer this question as infrared lines. The remainder of the stellar energy quickly'. The lifetime of a grain depends strongly on {in optically thick compact H II regions) will be con ils chemical and physical characteristics, and to verted to continuum infrared radiation by dust. The morrow 1 hope to make a few remarks on this. If you conclusion is that the observed infrared radiation can give someone a (enperature and tell him what ihe not be due to discrete line emission, but the line radi chemical properties of the grains are he can give you a ation is certainly there and should be searched for. lifetime. However. I wilt say this >a grain which is close to a star and is made of ice will live in the order B. BAUCK: Perhaps far-infrared emission lines of only a few hundred years. Close to stars, therefore, from molecules in high density (n^ ~ 10* cm"3) ice grains do not survive. Other types of grain, which regions contribute to the contamination of the far- I will be discussing tumor row, survive much longci. infrared spectrum. J. EMERSON: In response to Dr. Simon's plea for V. PETR0SIAN: Molecular lines even though 100t,>m observations in (he Orion region. 1 can report m&srng in the type of clouds we are talking aboul. a preliminary result obtained during a balloon flight where the temperatures are not very high, would not in Argentina. We found emission in the 40 • 3Sûpm contaminate the continuum very much. We riave just band near the southern CO peak (CO206.9-16.5) in started some calculations for the OH molecule and the diffuse dark nebula Lynds 1630 [Tucker, Kutncr even wilh Hj densities up to 10s cm-3 you do not get & Thaddeus. Ap. J. 186. LI 3 (I973)J.HCN has been a very high surface brightness. 1.4. Radio Observations and Structure of H II Regions 103 NEW OBSERVATIONS OF H (I REGIONS AT 7.875.1 S.5. 31.4, OR 85 GHz Hugh M. Johnson Lockheed Missiles and Space Co., Palo Alio. California. USA ABSTRACT Observa turns of ,-,bout 3h regions are presented as on most of the material, especially as it relates lo a table of flu* densities in one to four frequenacs. previously published data iu various frequencies m- and also as maps of selected regions, or as spectral eluding the infrared, displays of some of them. Comments are also made 1. INTRODUCTION This paper summarises our most significant data Table 2 names each object and gives another iden on selected H II regions, or diffuse nebulae, taken in tification if available. In some cases this is the desig the radio-frequency continuum with the Haystack nation of an embedded star. Still another identifica Observatory'" 36.5 m telescope and with the 11 m tion of separate knots within H II region is by galac telescope of the National Radio Astronomy Observa tic G co-ordinates. The most specific identification is tory" at Kilt Peak, in 1971-73. Standard observing according to the right ascension and declination techniques at the respective observatories were fol employed at the telescope, shown in Table 2 after lowed. They were essentially outlined in work on precession to 1950. This is very important infor peculiar planeia.y nebulae [Johnson. 1973a] and on mation fot the assessment of the data of small ob the y Cygni supernova remnant and nebula [Johnson. jects, whose co-ordinates may not be known accu- 19741. Table I summarises some of the instrument parameters. Some of (lie new data arc combined with pre viously published material into selected spectral plots. Table 1. Telescope parameters Maps of certain objects are presented, but most of the data are simply flux densities with RMS errors and Frequency HPBW some associated data in Table 2. Observatory (GHz) ('arc) Haystack 7.875 4.4 on-off and some maps * Radio astronomy at the Haystack Observatory of the Not!he»11 Radio Astronomy Corporation is conducted 15.S 2.2 on-off and «villi support from the Nation») Science Foundation. some maps 31.4 3.7 on-off ** Operated by Associated Universities, Inc.. under contract 85 with the National Science Foundation. 104 II M JOHNSON TaMe - V» railif-trtqutm-% -t taiely to a small fraction of the HPBW. Some negative tions of S ) 38. S 152. and )C 423. He also provided results of the on-off technique, not given here, may co-ordinates of Hobble's anonymous ntba}* and of have come primarily fay direction of the teklC0|wr to NGC 2359, which differ from (he ones tued in imprécise co-ordinates. Two s*ts of co-oidinates for Table 2. namely « = «fc»"*»»*, « = + 18°43.0' IC 1470 simply show a revision bslween different ( 1950) and o = 07*> 16m 12.9s, 6 = -13°08.4" < 1950). observations. We are greatly indebted to Dr. T.R. Gull respectively. (1973J for providing coordinates based on measure Table 2 continues with a corrected, gaussian- ments of Palomar Sky Surrey charts for the observa source (FWHM) = Siliratnl \ Me/gei jiW] Observed tint density in nuque ate multiplied by j lac tor ils U5' to allow Jansky. illl^ftni'll/'i t»llows under une or • 'he F-WHM ul source m the telescope beams ol more i>l the ttim frequencies Hux densities deter ! .- 1 This tact.it is detmcii hv H.urs et al \i''^\ mined wilh the nii-ull technique ate go.'n with RMS nher 3 disc or a gaussian dismhution .it the llux emu weighted according to inverse-square RMS <>l j ie extended source We have assumed gaussian in series nt integrations. When no RMSettor i«. given, ihe . -eductions ot all sources. I'nless lurthcr specified, flux density is a product of the mapping programs ot i spectral pluts ot published data in this paper are the Haystack Observatory telescope No error is com . NC cited in the Max-Planck-Institut ftir Radio- puted in these programs. Ihe integrated flux density t -mmie (Honnl Catalog of Sharpless H il Regions is alwa\s calibrated by a similai map ol DR 21 using i «iliotet. I''73|. which is a very useful co^ua- Item's |1''72| flux densities Reprodiii_ed maps are alwavs in a grid ot I(>50 co-ordinates. Atmospheric DISCUSSION OF SELECTED DATA (al RCW i:; This is probably FIR source bles OVI-sequcnce nuclei nI planetary nenulae such HI 1 23 IHoftmann et al. |9"M| - although identi as NGC 5189. we do not believe that G2 4+I 4 is a fied h> ii.ciit wiiii RC"A iZt - and MR source planetary. The distance b nol yet known for the LT1. !'• Itmerson el al.. I"73|. observed also by determination of the excitation parameter L". This Brown & Urodcrick | 19731. who measured would distinguish between a planetary-nebula nucleus S1K5 (iHz) = 22.2 +• <>.f> Jy using the same telescope and population-! hoi star. as ourselves If we correct our observed flux density i .J G6.4-0.5 This is HFE source 44. of interest by rij/SZ,' = 31 by employing Shaver & Goss's beca jse it is apparently a knot in the supernova rem |i*»70| corrected (FWHM) - 1-'»' al 5 Gill, we have nant W28. The spectral index of G6.4-0.5 is 0-4 S|85 GHz) = 23 + 9 Jy. which appears to be in good bet»-«n 408 and 5000 MHz. and there is an Ha fea agreement with Brown & Broderick*; value. However, ture IS' in diameter around the peak [Milne & Wil there are ambiguities because ihey quote Shaver & son. 1971]. Derived S(5GHz> = 6Jy according to Goss's uncorrected FWHM = 4.3' x 4.5' as the critical thar Jata. but our S(31.4 GHz) = 7+ 3.5 Jy after cor source size alongside their observed flux density, and rection by iyilj.' = 4.0 based on the 408 MHz dat- those dimensions would give £ij/$2 ' = 14.4. Also. s of iver & Goss [1970|. This suggests that Brown &. Broderick do not publish the a,6 of their G6- u.5 is predominantly thermal between 5 and 31.4 GHz. (b| G 2.4+1.4: Previous observations of this object figure 2. Spectrum of MS. as in Figure 1 (e) MS: The nebula haï been observed by several groups from lOjim io ihe FIR |cf. Wynn-Williams & Becklin. 1974J, and Johnson 11973c] has shown lhai ihe stars of the associated cluster. NGC 65.10, supply more power than the pains radiate by a factor in excess of 10. The radio-frequency spectrum (Fig- 2) is FigurrJ. Map of the region nf GI2.S0 2 at unexpectedly rougher than that of M20 (Fig. 1). 7.875 GHz in contour* of antenna tempe (0 G12.8-0.2: This source illustrates several kinds rature from OK to 5.0K in Heps of of difficulties in ihe co-ordination of daia. In Table 2 0.5 A. we repeat the query expressed in the MPI Catalog [Angerhofer. 1973) that the radio source G12.8-0.2 though if is included in the area of that optical region. We also believe that Hoffmann el al.'s (19711 identification of FIR HFE 50 with S40 is not likely, although HFE 50 is surely identifiable with Gl 2.8-0.2. Ollhof & Van Duinen |1973) probably observed this source at 71 • 95 /im and called il W33, although they do not report the observed a£ We give two maps. Figures 3 ana 4 , and the spectrum. Fig ure 5. Brown & Broderick [1973J report S(85 GHz) = 28.S + 2.2 Jy alongside a critical source size of 4' x 5' from Altenhof et al. 11970] - From our maps, we estimate Figure 5. Spectrum of 012. H-0.2. as in figure 7 .Q.Ay 5 51 20 31 00 30™40" S0™20' figure H. Map of the region of fC 423 at IS. 5 (iff: in contours of antenna temperature /'mm 0 K to 0.10 A in steps of '!. 05 A" (k) S 152: According lo Frogel & Persson (1972]. nearly all of the 1.6 to 3.5 um llux comes from a region corresponding in size to the dense image on the ted Palumar Sky Survey orint. which n 2' [Sharpless. 1959). (I) IC 1470: We give a map. Figure 6, and spec rf«W 0.-00- 03-00- 03-00- trum. Figure 7. with published data from Terzian et al. (1973| and cited by Israel et al. (1973], as well as new Table 2 data. At 7.875 GHz, the flux density ? 6. Map of the region of IC1470 at integrated in the map is plotted rather than the other 7.875 GHz in contours of antenna tempe datum, while S(15.5 GHz) and $31.4 GHz) are cor rature from OK to 0.4 K in steps of rected for the (FW HM) of the two components. A and 0.1 K. B, defined by Israel et al. These are at a single centre: a = 23h03m04.6s. 5 = +59°58'29" (1950). It differs from either of the positions used for our on-off data. The result is to require a larger correction than we • have actually made for our plots in Figure 7. (m) Ced 45 [Cederblad.19461 The position is that of the catalogued exciting star, TOri, Type B2 III. ' \ (n) IC 423: The map. Figure 8. shows at least one peak above noise, but not : : the position [Gull, I ' 1973] of the curious 2' x 2' [L/nds, 1965] or 6' x 3" [Dorschner & GQrtler, 1963], blue 'smoke-ring', 1 1 1 which is probably a reflection nebula. The Table 2 . .10 flux density is simply integrated in the mapped area, (o) NGC 1977: This nebula is often confused Figure 7. Spectrum of IC 1470. as in Figure? with NGC 1975, which is 10" north of it, but NGC 1977 is the one nearest the co-ordinates of the ear co-ordinates used in Table 2 On llic b;iM\ ot then Figure 11. Map of the region of IC 426 at 15.5 GHz in contours of antenna temperature from OKtoO.lOKtn steps ofO. OS K. SJ-W OHSI KVATIONS OI- II II RrCIONS 109 L Figure 12 Spectrum nf .VW 2024. as m Figure I uICMïl Figure IJ Spectrum ••] \(IC2JW. as in Figure I. 3. SUMMARY The objectives nf this paper have been tn puhlish sition and co-ordination of the lesulis. and to point new radio-frequency-continuum data for a number of oui other interesting, published data of some of the bmall. 'circumslcllar' H II regions, to discuss some of same regions. (lie difficulties and ambiguities apparent in the acqui- 4. ACKNOWLEDGEMENTS I wish to thank the Directors of the National dune partly under the Lockheed Independent Radio Aslronnmy Observatory and (he Haysiack Research Program and partly under contracts NAS 2 - Observatory for granting telescope lime, and their 7842 and NAS 5-23340 with NASA. staff for indispensable assistance. The work has been REFERENCES 1. Altcnhoff, W.J., Downcs, D.. Goad. L., Maxwell, 11. (Joss, W.M & Shaver. P.A.. Ap. J. {Lett.) 154. A. & Rinehari. R„ Astnm. Astrophys. Suppl. 1, L75(l%8). 319(1970). 12. Goss. W.M. & Shaver. P.A.. Australian J. Phys. 2. Angerhofer. P., private communication, 1973. Ap. SuppL.tto. 14,1 (1970). 3. Bairs, J.W.M., Mezger, P.C. & Wendker, H„ Ap. J. 13. Gull, T.R.. private communication. 1973. 142, 1220965). 14. Hoffmann, W.F., Frederick, C.L. & Emery. RJ. 4. Blanco. V., Kunkcl, W„ lliltner, W.A., Lynga.G.. Ap. J. (Lett.) 170. L89(I97I). Bradt, H-, Clark, G., Naranan. S., Rappaport, S.. 15. Israel. F.P., Habing, HJ. & de Jong, T.. Astron. &Spada,G..Ap.J. 152,1015(1968). Astrophys. 27. 143(1973). 5. Brown, R.L. & Broderick, J.J., Ap. J. 181, 125 16. Johnson. H.U..AP.J. 167,491 (1971). (1973). 17. Johnson. H.M..A/«n. Soc. Rov. Set. Uège.Set. 6. 6. Ccderblad. S., Medd. f. Lunds Astron. Obs.. S. 121 (1973a). Ser. II. No. 119(1946). 18. Johnson, H.M., Ap. J. ILttt.) 180. L7 (1973b). 7. Dent,W.A..4>. '. 177,93(1972). 19. Johnson, H.M., Ap. J. 182.497 ( 1973c). 8. Dorschner, J. & Gurller, J., AN 287, 257 ( 1963). 20. Johnson, H.M., submitted to Ap. 1. t. Emerson. J.P., Jennings, R.E. & Moorwood, 21. Johnson, H.M. & Hogg, D.E.. Ap. J. 142, 1033 A.F.M.,Ap.J. 184,401 (1973). (1965). 10. Frogel. J.A. & Persson, S.E.,Ap. / 178, 667 22. Khromov, G.S. 4 Kohouttk. L, BAC, 19, 90 11972* (1968). liM JOHNSON iy Lynds. h I.Ap. J Suppl. 12.16341465). 28. Sharpless, S.. Ap. J. Suppl 4. 257 ( W>) ;4. Milne. O.K. & Wilson. T.1-. Aitnm. Autophys. 2». Shavct. P A. A Goss. W M., Auvnlian J. Phys. Ap. Suppl. No. 14, 133 ( W70). ;5. Oliliof. H. A Van Du m en. RJ . Asmm. Astro- .10. Smith. LI- & Allet, LU.. Ap. J. 157. 1245 phys. 29.31 3| W~3k HWJ). >. Perek, I A kohtmick. L. Catalogue of Galactic 31. Tercian. Y.. Dcnnison. B. A Balick. B.. ft/ft ASP Planetary Nebulae iPrague Acadetnia). I**t>7. 85,806(1*173). r.Schraml. J. & Mezget. P.G.. Ap. J. 156. 2h*> M. Wynn-Wilhams, C.G. A Bccklin. B.K.. Pub. ASP 86.5(1974). B. BAL1CK Could you please compare the mor speciral index, while NGC 7635 is thermal. The dif phological properties of G2.4 + 1.4 with those of ferences between the nebular may be a consequence NGC 7635, wtiicri was discussed extensively yester of the difference in velocity of ejection from the day'' stars. H.M. JOHNSON: The relative distances are un J.A. FROGEL: W33 is probably similar in the known, so scale factors nay be quite different. radio to G351.6-1.3 which Brown and Broderick have G 2.4 + 1.4 is a 'rougher' ellipse and might be more shown to consist of a central component which is self filamentary, were il better resohed. Tne exciting star absorbed at low frequencies and a much more ex- cf NGC 7635 i£ : *»e™!iï* Of tyr*. w*>il* 'bat of •Ti^ed, !OOTI der!ii!v efi»f!n«e. Both rsfiio sources G 2.4+ 1.4 falls in Smith and Allen's O VI sequence (G351.6 and W33) contain very compaci « 10") of Wolf-Rayet-like types of planetary nebulae nuclei, infrared sources. In the case of G351.6, the 1R source with extreme Une broadening equivalent to as much corresponds in size and position with *he compaci as I04 km/ï. Both surs aie far off centre, unlike PN source found by Brown and Broderick. nuclei. G 2.4+1.4 shows a non-thermal power-law HIGH-RESOLUTION RADIO OBSERVATIONS OF THE SOURCES NEAR KJ-50 Mullard Radio Astronomy Observatory.Cavendish Laboratory, Cambridge. UK The group of radio sources neat the optical object K3-50 itself having an unusually high brightness lem- K3-50 has been observed at S GHz with the Cam- ' perature. It is particularly interesting to compare the bridge S km telescope-Two of the sources show high- radio infrared and optical observations of these den si I v enmnart «nirtiire, the one coir.cidsr.t nïtï; sources. 1. INTRODUCTION The optical objects K3-50 and NGC 6857 lie al., 1970; Buhl & Snyder, 1973]. In addition, a within a very complex and densely populated region 1720 MHz OH source is fairly conclusively associated of the sky. They are associated with a group of com with the more northerly object. Component C pact 11II regions contained within the diffuse nebula (Wynn-WiniarraetaL, 1974). Sliarpless 100, which in turn lies within the larger This paper reports observations at a frequency of radio complex W58. This group was resolved by 5 GHz with the Cambridge 5 km synthesis telescope, Wynn-Willianu |I969], using the Cambridge 1 mile revealing the detailed structure of the two stronger telescope at a frequency of 2.7 GHz, into four dis components A and C. The instrument has a half- tinct sources having a maximum separation of 3.3'. power beamwidth, at this frequency and declination, Component A is coincident with K3-50 and there is a of 2.0" in RA and 3.6" in declination. Observations diffuse component connected with the more extend have also been made to obtain the flux densities at ed optical source NGC 6857. K3-S0 itself is a strong 408 and 1407 MHz using the 1 mile telescope, whose infrared source (Neugebauer & Garmire, 1970] and half-power beamwidths in RA are 80" and 23", res several molecular and recombination lines have also pectively (and larger by a factor of cosec 5 in been discovered in association with it [Zuckerman et declination). 2. THE SOURCE COMPONENTS The map of component A at 5 GHz is shown in ably high peak brigntness temperature of 8600 Figure 1. At this resolution, it appears as a strong + 1000 K, which places an interesting lower limit on compact object towards the eastern edge of a more the electron temperature. In particular, it produces diffuse crescent-shaped envelope. It has the remark strong evidence in favour of a non-LTE interpretation STILL A HARKIS of the HI(Na line, since the assumption ul LTh would imply an electron temperature of 7K) Q • 700K (Rubin & Turner, I969J. The source has a total flux density at SGIU of (4.0 + 0 5) x Iff3* W m"3 Hz'1. and the contour map is best explained in terms of a contribution of l.K x Iff3" W m"1 II?"' from the central source and 2.2 x Iff1* W m1 H/' from Ihc envelope. The northermost source. Component C. appears on the 5 GHz map (Fig. 21 as two compact conden sations deferred to as CI and V2 in order of increas J ing RA). »ith a more extended envelope surrounding -•i CI and a very diffuse envelope surrounding them both. The flux densities derived from the contour map are recorded in Table I. Figure 3 shows the 1407 MHz map. m which the individual sources are distinguishable though not completely separated. At 408 MHz. the whole com r.-L plex of Components A and B and NGC 6857 appeais as a single unresolved source. Conumr map of Component A ai 5 GHz with nmfi/mwt fnr JQfll/l Jh* Contour map of Component C at 5 GHz with co-ordinates for 1950.0. The con tour interval is 248 K. The cross marks the position of the 1120 MHz OH source { Wynn-Williams et al., 1974} and the shaded ellipse represents the half-power beam area. Contour map of the region a! 1407 MHz with co-ordinates for 1950.0. The con tour interval is 163 K. Negative contours are shown dotted, and the shaded ellipse represents the half-power beam area. RADII) OBSERVATIONS OF SOURCES NEAR K3-5CI Tabic I. Flux densities ofthe component! S 40H S]407 •V»ys 1.1 iO.H 4.0! :0.5 f Condensai 1^ f-.nvelnpe 1.5 • 0.5 : ..i J OH :OÎ o.R 1f n (17 ; i) J 24- OK 34! :05< J1 Inne r: r envelope 1 4 VJuter envelope 0.8 y DISCUSSION The esiimalcs of I lie distance to this complex ot star (assumed O-B) from the photometric results of oiijcU* 4ic iiiiiici uiiLcnain, being dependent on the Uller&bhao |!Vb8J. interpretation of radial velocity measurements. However, in the case of K3-50 they find that the Several measurements have now been made of radial apparent value of C increases systematically as longer velocities in various molecular lines, most of which wavelength measurements are used, and a comparison have values between 20 and -27km/s. This is in of the radio and infrared data implies a visual absorp moderate agreement with the results obtained for the tion of 20m or more. If K3-50 and NGC 6857 are extensive neutral hydrogen cloud which is observed genuinely associated in space, then it is apparent that along this line of sight (Thompson et al., 1969; Bridle there is a visual absorption corresponding to C^2 & Kestevcn. 1970) and the 21cm line velocities along the line of sight and that the peculiar behaviour IBohuski ct al.. 1970: Georgelin et al., 1973] and of K3-50 is due to the presence of the dense sur indicates a kinematic distance of about 9 kpc, which rounding dust cloud which produces the strong infra is surprisingly large, considering that K3-50 is an opti red excess observed by Neugebauer & Garmue cal object and that the Cygnus region is in general 11970J. very heavily obscured, [t is interesting that the A possible explanation for this behaviour, which 1720 MHz OH feature (which coincides almost exact is favoured by Persson & Frogel, is that the optical ly with CI; see Pig. 2) shows a rather less negative emission is only seen where the depth of the dust is radial velocity than the other lines [about -13 km/s; relatively small, whereas the bulk of the source pro Downcs, 1970|, which might indicate the existence ducing the radio emission is much more heavily ob of significant peculiar motions of the sources. How scured. Certainly this would explain the claimed size ever, if such motions were to account for a substan discrepancy between the optical and radio objects. tial part uf the radial velocities, the close agreement However, Persson & Frogel also mention the sugges with the neutral hydrogen values would be somewhat tion made by Jones [1973] that the 'effective'depth surprising. of the dust could fall off systematically with increas Persson & Frogel |I974] have made spectro- ing wavelength in the optical region, due to the scat photometric observations of K3-50 and NCC 6857 tering properties of the obscuring particles. Here it is and have obtained several estimates of (he expected interesting to note that, if this explanation is adop extinction in HP by comparing the observed intensi ted, the relative effective depths deduced from the ties in different pairs of hydrogen lines. They obtain a spectrophotometry; results are in quite reasonable value of C |= A log l(H0)] of about 2 for NGC 68S7, quantitative agreement with the predictions of Jones' formulae, for the range in albedo and phase para corresponding to an Av of around 4.3m. This is very similar to the value obtained for the central exciting meter suggested by Wickramasinghe [1970]. How- STtLLA HARKIS e\er, such a tit cm only he tentative since the scatter- prrcne nature of ihc interstellar pains. Il would also be ,ti(; model IN necess-rih grcatK oversimplified, and mietesling to obtain an improved optical position tor :heie is still much work to he done in establishing the comparison with that of the radio peak. 4. ACKNOWLEDGEMENTS I 4,ir jMJietul in several member «I the Oepait Mr A.N. Argue for many useful discussions. I also nitfiu Mi then help and encouragement, and in parti- acknowledge receipt of an SRC Research Student- culai u> l>i PI Scott. Dr. C.G. ttynn-Williatmand ship REFERENCES J. Bohuski, TJ-. Rubm. R.H & Smith, M.G.Piibf. tlcrrjl6i.U>HI970). Asir. S"c. ftrri,rîr82.9t3(l970). 9. Persson, SJ-. & Frogel, J.A.. Astrophys. J. 188. : Bridle. A.H. & Kesteven. M.J.L. Asir. J. 75.90: 523(1974). (|9~0P. 10. Rubin. R.H. & Turner. %£.. Asmtphvs. J. (Lett.) ? Buhl. D. & Snyder. LE.. Asirvphys. J. ISO. 711 157. L41 (1969,1. (W73J. 11. Thompson. A.R., Colvin, R.S. & Hughes. M.P.. 4. Downes. V.. Astrophys. Leu. 5.53 ( 1170}. Asrmpftys.J. 158.939(19691. 5.Georgelin. V.M.. Georgelm. Y.P. & Roux. S.. 12. Wynn-WiHjams. C.G.. Astrophys. Lett. 3. 195 Asir. Asrrnphys. 25,337 < 1973). (1969). O.Jones. T.W.. PubL Asir. Soc Pacific 85. 811 l3.Wynn-Wiliiams, C.C.. Werner, M.W. & Wilson, (19731. WJ..Astrophys. J. 187.41 (1974). 7. Liller. W. & Shao. C.V., Planetary Nebulae 11AU 14. Wickramasinglie. N.C., PubL Astr. Soc. Japan 22, Symposium No. 34). (Ed. D.E. Osterbrock and 85(1970). C.R. O'Dell). Reidel, Dordrecbt-Holhnd, J°68, 15. Zuckerman, B.. Buhl. D, Palmer. P. & Snyder, p. 320. L.E.. Awvphyi. J. 160,485(1970). 8. Neugebauer. G. & Garmire. G.. Astntphys. J. DISCUSSION HJ. HABIN'G: I want to mention thai Israel at map indicates a fairly well-defined distinction be- Leiden, using the Westerburk synthesis radio telee- tween the dense compact object and the more diffuse scope also observed the K3-S0 complex at 5 GHz. Hle envelope, so that 1 have calculated a separate electron had less resolving power and more sensitivity. Give:n density for each of these figions. I have also calcu- these instrumental difference*, his results confirm lated the spectrum by treating them as distinct ob- your results as well as one might expect. This agreee- jecls and adding them together, and this gives a mode- ment reassures us that synthesis m»ps. if mndc witIh rntcly good fit to the lo«'-'equ(-ncy observations. care, aie at present reliable also in the details. You did not discuss die spectrum of K3-50, app- J. MAYO GREENBI RG: What method did you parently because of a lack of time. Do you agree thaat use to separate out effects of scattering from the the shape of the spectrum at optically deep wavee- extinction when the dust is included in the telescope lengths supports density variations in the source? apeiture? I might mention here that I made a rather simple minded, but detailed, calculation of this effect STELLA HARRIS: Certainly (he specirum coulId in circumstellai distributions (presented at 1971 not be fitted by a uniform density model. The 5 GHlz Liege Symposium). RADIO DBSMtVATIONSOI- SOL'R< IS NMR K3-S0 115 STELLA HARRIS: My approach too was very oxlCf1 cm"3 and a linear si/.e of aboui 0 ' p>_ [In- siinplc-inin.'îd. I merely considered the two extreme thermal spectrum probably turns over at jlmm cases of complete forward-scaticnng (probably valid lOtiH/. but more high-resolution observations al dit- over a fair range of phase parameters for sufficiently ferent frequencies are needed to confirm tins. high albedos) and the Eddinptnn approximation of isotropic radiation (valid for small values of phase parameter, provided the albedo does no' become ton E.L. BECK. IN: There is no indication thai the small). H II region is physically the same object that is radi ating in the infrared, in fact Ihere is good evidence 11. RAL1CK: What is the density and linear si/e of thai it is not. the optically thick component and al wbat radio fre quency is the entire nebula optically thin? STELLA HARRIS: This is the main problem. There is no direct evidence that any of these repions STELLA HARRIS: The optically thick compo are related, .iut it is just the best assumption you can nent of K3-50 has an electron density of around make until there is definite evidence to the conirary. A HIGH-RESOLUTION STUDY OF THE H II REGION W 3 R.H. Harten (read by H.J. Habing) Stcrrrwacht, Huygens Laboratory. Leiden. The Netherlands ABSTRACT Observations of the H 11 region W 3 I INTRODUCTION The radio source W3(OH), also known as an isolated object with no associated courtes ot ex C 133.9+ 1.1. is a classic case of a compact K II tended emission, but recent observations by Wink ei region. The source is a strong point-like one with no al. [1973] have shown that there is evidence for a corresponding optical emission detected. There are second source near the main one. In several H II two infrared sources in the region {Wynn-Williamset regions, OH emission has been found to be associated al., 1972]. One is coincident with the main radio- with a weaker source situated near a strong source source. There are both OH and Hi O maser sources in (Habing et al.. 1974]. In order to check for this type the region around the source. It is believed that it is a of correlation and for any source-associated faint young region, possibly less than 10* years old emission, observations with high resolution and high IMathews, 1969], surrounding a recently contracted sensitivity were desirable. massive star. Originally, il was believed that this was 2. OBSERVATIONS Observations of this object were made with the beam sidelobe and grating ring effects. To obtain the Westerbork Synthesis Radio Telescope at wavelengths maximum resolution, a 6 cm map was processed with of 6, 21 and 50cm (4.995, ..415 and 0.610GHz). only the longest spadngs. This resulted in a beam of The rugh sensitivity and dynamic range of the system 4 x 4.4". made a search for low-intensity emission associated Our observations show that the source G I33.9 + with this source feasible. The observations were cali 1.1 is a complex of at least four sources embedded in brated with more than normal accuracy to ensure as a faint extended component. Figure 1 shows a map of large a dynamic range as possible, since the main W 3 the region made at 6 cm wavelength. Table 1 lists the source is quite nearby. The maps at all three wave- positions and fluxes of the different components. lengths were processed using the clean procedure. Our observations confirm the presence of com This allowed us to remove the effects of the synthesis ponent B found by Wink et al. Il appears thai their H. 11. MARTIN ^ ( Figure 1. Contour map ofW3I0H) al 4.995 GHz. Coniour values are 3, 6. 9.12, 15. 25 through 275 in steps of 25 tTLf.u. (1 ntf.u, = Iff19 Wm* Hz~' ). Table i. Source components for WIOHÎ Right ascension Declination HPW s Component 4.995 (1950) (1950) (are s) (f.u.) W3(0H)A 02h23m16.S011.05 61°38'57.7 ± .4 <2 0.33 ±.01 W3(0H)B 02 23 17.20 t.07 61 39 01.4 ±5 <2 0.035 ± .007 W3(0H)C 02 23 17.25 ±.07 61 38 52.9 ± .5 6±3 0.042 ± .007 W3(0H)D 02 23 17.87 ±.07 61 3B45.8 ±.S 0.007 ± .005 Uhi»-RrSfiLVTtON SI H H Rt-UON W3 (Ofli 1)9 Figure 2 lift nf flux density ci frequency of the source W 31 Off) A. Triangle* indicate measurement), presented in this paper. Solid tîntes are those < if other authors. Open circles indicate the flux for the en tire region, based on the sum of all known components. Note that the itvo lowest frequency- points are circled. The dashed line indicates a slope n = I. fluxes fur component B are too high and n is quite likely that they were confused hy the other sources in 1 he field. It ont lums the fluxes of components B, C and [>. then the agreement in flux is reasonable. The 21 and SU cm observations indicate a point source with a slight southern extension in the direction of component (', further supporting the presence of the additional components. The i\u\ densities of the source at Ihe lower fre quencies are quite Irgh and can not be explained by an extrapolation of the high-frequency fluxes assum ing a single compact, optically thick source. Figure 2 shows a plot of flux density as a function of fre quency for the source. The encircled points at the lower frequencies represent the flux of the total re gion since it was not possible to separate out the contributions linm the different components. The open circles at Ihe higher frequencies represent an estimalc of the loi a! flux of the region, based on a sum of all known components. At best these are lower limits. A line with a slope of n = \ has been drawn in to show how closely all of the fluxes can be fitted. A spectral index of n = 1 is indicative of a region thai has both opikally thin and optically thick radiation. Because of this mix of radiation, it is diffi cult to derive any source parameters based on the lower frequency data. The positional cortelation between the different conlinuum sources and the 1R. OH and H20 sources is shown in Figure 3. It appears that the OH sources are associated with the main source A. but they may lie in a region between sources A and C. The Ha0 Figure 3. Relative positions of the different contin source is not associated with any point source, but it uum, OH. IR and H30 sources. Triangles docs lie in a region of extended emission. The IR indicate continuum radio source positions source IR 8 appears to be associated with Ihe main (solid ones indicate positions given in this source. IR9 (Wynn-Williamset a!., 1972], on the paper). Solid circles indicate OH sources. other hand, is not associated with any source. An Open circles indicate IR sources. Solid upper limit on the 6 cm flux at this position is squares indicate H2 O sources. The dashed 2 m.f.u. lines indicate tlte 9 m.f.u. contour. 120 R.II. HARTVN 3. CONCLUSIONS Our observations of ihe W *tOHl region haw sets of 4 mix of compact and diffuse emission shown it to be a complex of sources embedded in a sources. An overall spectral index of n s I further faint extended component. Tiie flux density of the supports this view. The OH sources appeal to be asso rep Lin ji lowet frequencies is too high for a single ciated with the main cluster of continuum sources, compact source. It can be explained if the region con- while the HjO source is not correlated with any. REFERENCES 1 Habing. H.J.. Goss. W.M.. Matthew. H.E. A Aitrvn & Asiruphys. 22. 251 I I'm). Winnbcrg, A.. Asmm. 6 Aitrophyt.. in press. 4. Wynn-Williams. C.G.. Becklin, E.E. & Neuge- : Mathews. W.G.. Astrophyi. J. 157. 58? ( l<*bt\. biuei. G.,AI\ftAS 160. 111972). y *'mk. JE.. Allenhoff. WJ. & Webster. WJ. Jr.. DISCUSSION A.P WHITWORTH: Do you expect that, as bet H. HABING: There is a law in instrument build ter and better resolution becomes available, objects ing stating thai once you have built an instrument, it such as W3 L Hart & A. Pedlar Nuffield Radio Astronomy Laboratories. Jodrell Bank. Cheshire. UK Oiaissun et al. fl('72| have detected recombi lines. In this paper we report similar, but more sensi nation line emission which could correspond lu an tive, observations of the 166a line which confirm the clement or elements with mass greater than carbon in above result. the 1 S7a and l5Ra I. THE OBSERVATIONS The recombination line measurements were car frequency analysis was achieved by means of the ried out in April-May of 1973 using the MK IA 250 ft 256 channel autocorrelation spectrometer [Davies et telescope which gave a half-power beamwidlh of al.. 1969} using a bandwidth of 1.25 MHz. The fre 13'x 13' at A21 cm. The telescope receiver was quency response was 8.6 kHz (I.Skm/s) in half- equipped with an uncooled parametric amplifier, power width. A method of frequency switching by which resulted in a system temperature of 120 K. The 1.2 MHz was employed. Table I. Gaussian analysis of observed 166aspectra Dec(!950) Line TA (K) (kHz) (km/s) NGC 2024 05h39ml2s -1.934° WHI1) 0.3010.02 172 19 3.710.7 H4HN) <0.02 H(HI) O.I7±0.03 29.116.0 8.810.5 * Relative to catbon rest frequency. 1 HART A A PIPLAk 2. THE RESULTS The lft»a spevttum for N(îC 202A is. shown in lo the hydinger) and anomalous features ol ihc spec Hguic 1 A hnt'Ji Ktrflirw has been removed (iauv trum. No helium emission wa* apparent The result* Mans hj\e been titled, using a teasl-squaics method. of the (Russian lilting are pven in 1 able I VELOC'TV RELAT'VC TO LSO Figure I. fa) The I flfta spectrum nf \(JC 2024 showing the original data with linear baseline returned Hie evntinuum line shows the best Gaussian fit .'p / The residual after subtracting the Gaussian fit. 3. DISCUSSION fi'/ 77rp Hydrogen Features shifted relative to the carbon line hy 8.4 km/s. This feature is greater than direc times peak-ro-pcak no:sc, The 166a hydrogen profile of NCC 2024 displays and was observed on several independent batches of an obvious asymmetry. This was first noticed by Ball data. ei d. (I970J in the HlS7a spectrum. This emission It is possible that (his feature is a dopplcr-shiftcd un be decomposed into two Gaussians: one corre carbon line fa shift of 8.4 km/s is quik modest). If sponds to ihe H II region and the other to the cool, this were the case, we would expect to see a corre partially ionised HI region presumably surrounding sponding H I feature in the 11166a line. If we assume the H11 region. The width of the H I feature can be that the doppler-shifted carbon cloud contains the compared to the CI feature resulting in an ion tempe same ratio of hydrogen-lo-catbon ions as the main rature of 480 *||§K and RMS turbulence of 3 km/* cloud, then the H ( feature should have an antenna (this assumes that the two ions have the same spatial temperature of 0.0S K and a velocity of I kmfs. No extent and temperature). The ratio of the intensity of emission greater than 0.03 K seems evident on the the H I line to the C I line is measured to be 0.86 residual of Figure lb. It is possible thai the Iwo + 0.3. clouds have different properties; however, the atomic This indicates a large reduction in the number of hydrogen absorption spectrum (Fig. 2) does not show J 3.6 eV photons compared with 11.2 eV photons in a cloud which corresponds in velocity to the 'doppler- the cool clouds near NCC 2024. shifted* carix « line, and it is difficult lo conceive of a cloud which contains ionised carbon and no atomic (a) Tlic Anomalous Features or ionised hjdrogen. Thus it s likely, as suggested by Chaisson el a)., The 166a spectrum shows a definite feature thai the feaure can be attributed to recombination RADIO KtCOMMNATlON 1.1 NFS PROM NW 2024 lnu- omission frtint elements heavier than carbon, pos- ,lf sihl> ~4Mg. 2<,Si. i2S and 5bFe. This is plausible as ,' i liesc elements all have lower ionisation potentials than '"' liyriropcn, and a total abundance MY- H\ number of ' ^ __ larhun Willi ilic sign all "-noise ami lu-querny reso lution of the present observations n is not possihle ., i rvj^^/v-y^-- to distinguish which elements arc present li is most * likely that the doppler broadening at the individual a " "'**' elements nu> cause ihem lo ririuin indistinguishable 5 Jf ~ "~— unless extremely high wtisitivny measurements allow - «t some degree ol deconvoluiion to he achieved * ^ / la! Vie IMa carlum line spectrum of StlC 2024 shown together with fhf ato mic hydrogen, (c) IM " MHz Oil and (d) formaldehyde absorption spectra Tlte velocity scale is the same fur all four spectra. RELATIVE TO LB» IKmMt : REFERENCES Ball, J.A.. Cesarsky. D.A., Dupree. A.K., Cold- Cesarsky. D.A.. Astrophys. J. 173. L131 ( l. berg. L & Liliey. A.E.. Astrophys. J. 162. L25 3. Davies. R.D.. Ponsonby. J.E.B.. Pointon. L. ide < l*»70). Jagcr. C. Abfwr 222.933( 1969). Chaisson, E.J., Black. J.H.. Uuprec, A.K. & B. HALICK: The ratio of carbon to heavy ele- dcnce. It is interesting to note that the ratio of the merit recombination line intensities seems to vary H I to C I line in tern i tics varies between Orion A and from nebula to nebula somewhat. Have you any NGC 2024, indicalinj possible different UV fields, thoughts on this.' V. PETROSIAN: What limit do your observations A. PEDLAR: I do not think that the ratio is a give for He to H line intensity ratio? true measure of abundance. The heavier elements have different ionisation potentials from carbon and A. PEDLAR: The helium line integrated intensity until we know the UV field in the cool clouds il is b less than 15% of the hydrogen-line intensity, difficult lo predict their intensity with any confi- FORMA HON OF H II RtX.IONS BY BQ RADIO STARS WITH INFRARED EXCESS F Ysiag» Astro physical Observatory. Univrr.it> of Pa dot a. Italy ABSTRACT I"eculi.n slais characterised hy mttared excess panion have eject a which can he resealed bv mhei |Ailcn. \'f}\, radio emission and loihidden line* of techniques, e.g microwave detection «l f I) haloes in very ditterent ionisation poiennals. show absorption thelaie( siar lRt"+l0:i6 (Wilson et al . 1<>") hands imiicatiiie. tin- presence "I 4 late type giant If the radio emission of BO surs with mrrar^J rompait nebulae are found in V ](Ht> t'vj! and excess is ot thermal origin (as announced ïnr a le» <-\ HBV-175. whereas MWl .14*». MWt I", M; o ani) ihemt. we expect other nebulae surrounding siiniljr K Aqr aie surrounded hy emended nebulae. Low star-, to emit at radio frequencies. Stellar-like nebulae exciiaimri features ot stellar origin as ucll as inflated around BQ-IR stars ate also known tor MWf ]? jnd excess emanate hum tenions close to cenlral stats, III) M5h5 ICiatti el al.. l«74). Ml-; [o'Dell. while radii' emission is mostly due to the cxiended I*«.h|. RR Tel. VVHO. RX Pup. HD 33003(>. 11/ )~2. nebulae (in the case of M2-'> this miph' not hold, also, AS :i)I (Glass et al.. 1073). He 2-44:. M1-"M and the presence of late-lype ahsor|iiiun bands has not possibly M M»: (Allen et al.. I«v:j oi MUT' Mu yet been proved1 A concept in which mass ejected hy | S win pi et al.. lt>73|. The complete paper will he a laie-iypc star (ni spectral type M or O fotins a suhmir.ed fut publication in Asmuumy and Ann*- nebula exciied hy a hot companion, explains the phyucs. observations Other evnlved stars without such a aim- REFERENCES 1. Allen. D.A.. Mfl/HAS 161, I45(HJ73) 5. O'DeMCD-Astropiiys. J. 147, IS7(I<)6M 2. Allen. D.A. & Swinps. J P.. Asimpiiys. J. 174. 6. Swings. J.P. & Allen. D.A.. Astrophyi. Ixit. 14. 583(1472). 65(10731. 3. Ciatti, F., D'Odotico. S. & Mamniano. A., Astrim. 7. Wilson. WJ., Schwartz. P.R. & fcpstein. E.E.. Asimphys. (in press). Astmphys. J. 183. 8711 ll>73). 4. Glass. I.S. * Wehstei. H.L., MiVRAS 165, 285 (1973). OH AND THE EARLIEST EVOLUTION OF H il REGIONS Hi. Habing Stcrrewachl. Leiden.The Netherlands A nunc complete presentation of Hie observations Man Planck Institut (ur Radioastronomie Uonn. and fUvcn in tins i.ininhuinin will appear in (wo papers with W M diss and HE Matthew, ot "U- Kapte-n Hahtng et al.. 1*»"?4. Matthews ct al.. ll>"4. In this Astronomical Laboratory. Gromngen. The present pioiecl I vmrked togethei with A Wmnberp of ihe text is. however, largely my own responsibility 1. OUTUNE OF THE PROBLEM Sources ot OH emission can i^diviued into a num appro* ^ *'. or 7000 AL VLM measurements give ber of categories. Turner 11 ^70) has given criteria lor only relative positions The absolute position of some such a division- It appears that several newly dis ten Type I OH masers has been measured at Owens covered sources sometimes make a strict application Valley |Wy„n. Williams el al.. !974a[. bin these of Turner's classification dill'icull. although (he main observations do not lesolve the sources. Henceforth, features are still valid. ftrojdly speaking, there are we consider the Type I OH masers as pmnl source» tout categories til OH emission sources. The first cate with sues of at most a few seconds of arc. gory, almost coinciding with Turner's Type 1. con A general characteristic of Type I OH masers is sists of very small sources radiating mainly by stimu that tfiey occur in the immédiatv neighbourhood, i.e. lated emission in the main lines, though sometimes in within a few par sec. ot compact H II regions, that is 7 the l -0MHz line. Sources of this category have H II regions with d< I pc and EM > 101 cm"" pc. been found primarily neat or inside H 11 regions. Chance coincidences can be excluded. Since on dyna The second category probably corresponds to red. mical grounds compact H II regions are thought to be late-type stars. lliey also emit mainly stimulated very young (say. less than 20 000 yrl. h follows that emission, often in the loi- MHz line, although fre the Type I OH maser phenomenon occurs approxi quently main line emission is found. The third die- mately at the birth of massive stars. This indicates the gory consists of extended sources associated with importance of obtaining more insight into the physi dark clouds. The fourth category are the unclassifi- cal conditions near such masers. One approach is to able sources: in tacl a remarkably small sample. For study the continuum radio emission from OH masers. s.mplicity we also assign the few known 'Type lia Detailed mapping of radio contJrroum radiation has inasers' [ Tuinei, I970| to this category. been done for W3 OH (Baldwin et aL. 1973; Wink et Here wc restrict ourselves to the first category, al., 1973;Harten.this conference), for NGC 7538 the strauR masers with very small components and (Martin, 1973J,for ONI |Winnberget al.. 1973], for extreme brightness temperatures. They seem to be Ot\2 [Matthews et ai.. 1973]. and for ON3 [Israel. point sources, although in one or tw<» cases, e.g. 1974; Harris, this conference]. This has led to the W3 0H |Moran ci al.. 1968|, the sources have been discoveiy of very <:majl continuum sources, typically resolved by VLSI tech.iiques. In W3 OH, the maser of l" diameter, whose position agrees to within the uppears to cunsist of at least seven unresolved objects observational errors with the OH maser position. In distributed in a sort of ring with a diameter of view of 'he limited resolving power ()" at I kp* 12!* IN HABINt; itwjns I(XXI .\l'l. Ihe detailed positioning ol the con ol view _*S'i Isolated objects wetc also ohserved wild tinuum souuv with respect to the imp nl' OH maset the 100 m fcffelsberg telescope of tde Max Planck points (it. indeed, jli I>pc I ma>eii Jte similar to W.l Institute it Bonn ai 2 N cm MO.KC.Ib. I»eam wiiilh OUI remain* \nniewtiai uncertain "M"). MVe mappeJ in total eleven field;., iiiue Iwo Ue hase mapped continuum tadiMinu neat tint fields each contained two separate OH rnaserx teen Type I OH maser* whose absolute positions had Al h cm ou; detection limit was abom HI tnlti been deteimined previously In within a lew an (1 inlu = 1 milliflux unit = \0!" W m1 H? ' 1 A Mwndv In tins sample of thirteen masers we m homogeneous sphere ol ionised gas. optically deep at -Ended ONI and ON' Out main instrument was Ihe hem (ic. KM > 10" cm" pel and 500 A I' in dia tteMerhirk Synthesis Radio Televope tWSRTt. meter, would ptoduce just this flux at the harili il it winch we used ai hem 15 UH?.angular iesolut>on h" weie al a d Wan ce ot 1 kpc. Diamc-ie» ot this size _;e \ m strict", field ot new tO'i and at 21 ;m similar to (hose ol wide binaries among early type stars (I 4 Gtii; ançulai resolution 22" \ l-.rSin fi>". held |Van Albada.l'JhH, lip. 5|. DESCRIPTION OF MAIN RESULTS FRAGMENTATION In ail out fields we find compact 11II regions, is a remarkable phenomenon, noticed also by others, sesetal of which were known beforehand fiom work ils significance lies in the fact that on dynamical by others. In most fields we find more than one. This grounds these objects arc probably less than some A map of the radio continuum <&M\ radiation near G45.0and G45.5. obtained with the WSRT at 21 cm wavelength. The shaded ellipse in the lower left-hand comer represents the beam size. OH & lARt.JI ST I-VOLUTION Ol- H tl HHiJONS 12f) ^UWXiyr old, yel they appear as individual features, side associations with sizes of up in lOOpc. however, separated over some lOpc. Examples are ON:.W75, the optical data imply simultaneity on a lime scale ..I (M5.5. (145.0. W.U Prom other sti-dics une tan add at most 10s yr. whereas the radio observations reduce wM IMarlin. I<»72'. w I [Schraml &. Me/gcr. 1W>|. this to ICI4 yr. AI (his symposium Balick has drawn \V4'» |Wynn-Wiilianu. IW>,. NRAO 5H8/5H*» attention lo Ihe size of Harvard's loop 150 pc ) which lMuglies.lt llutler. 1W|.W5H (Israel. \<»4. Harris, encompasses several related spots ot active star for llus symposium) mation in Orion, An obvious imcipictation ol the phenomenon is I-ragmen ta I lun also incurs on a smaller scale, i.e lhat in an originally mui.li larger cloud,fragmentation most of ihe compact H N regions with sizes nt 1 pc look place, leading to several aciivc spots where indi appear lo consist ol several smaller sources, each ot vidual, though alniiisi simultaneous Mar lornialion which is very probably again a condensation nucleus. began Since Iragmcnlatiori is a process rather un- lor example. ON: consols of two complex II II .inienable lo theoretical analysis |see. eg . Spiivci. regions separated by Vpc bul each of these iwo 'Diffuse Mailer in Space". Seclionft2|. observation seems lo consist of iwo objects, separated by only ol the densities, si/es. mutual distances, time scales ol 0.6 pc. but partially merging. The besl example is of fragments and of the un fragmented cloud parts will course [)R21. which has been shown b; Harris he ol gicat value. Such data arc nol yel available. I»n |l*'7.1| to consisl of tour condensation nuclei, sepa H seems thai they may be derived from observations rated by at most 0..Î pc or 60 000 AU. in the near future. It seems therefore that compact HII regions never There s some indication that fragmentation oc come alone; ibey come in groups and in groups of curs even on a larger scale. Israel el al. |1'I73| bave groups. There is one source known In us which may indicated a region of ahmii I50pc diameter m (fie be an exception to this rule, ONI. Within 10 pc of Perseus Arm containing at least live compact H II (his source we find no indication of any other com regions. Also the sources G45.5 and G45.0 ire separ- pact H II region. Observations by Harris [1974J show aled over 60 pc I hip. 1). A long time ago. Blaajvv lhal ihe continuum source is at most a few thousand | )**£>2j argued thai the structure of associations indi- AU in diameter. cales riie existence of several condensation nuclei in- 3. OH MASERS AND CONTINUUM SOURCES In the complex fields containing several compact till regions, we found at 6cm also seven point sources, i.e. sources with diameters of less than 3" (Table I and Fig. -). In three cases we were able to measure the flux at higher frequencies with the 100 m dish at Effelsberg and found that the sources have a considerably higher flux. We therefore assume that we are dealing with optically deep bremsstrah- lung sources, similar to, but smaller than the nearby compact H li reginns. In other words, we assume that the point sources are earlier stages of the compact H 11 regions. It appears that all seven sources coincide with Type 1 OH masers. The RMS positional diffe rence is 1.5", corresponding lo a few thousand AU. Figure 2. A contour map of lite radio continuum radiation near OH45.47 +0.05 obtained with the WSRT at 6 cm wavelength. A cross marks the position of the OH maser. The ellipse in the lower right-hand comer 19-:z"0S* \$\?tô 19"lf55* represents the beam size. RAI19501 ILL lUBIWi TaMe I. OH maim and coincident continuum sources Ihilm.T Ihj Nimr 1 ptiiinclci ptitiri I|X .m'l IctR <' II» ' 111»» 10'° NGC^S3SS 111 5 t:o- :u jsori »>tHI 15."* t>^» • 2li MM) . Bild*in ci ai . )"-.).<4|l Some properties of the seven sources are given in resolution was poor, because of the unfavourable de Table 1, which also contains data on a few similar clination of the sources, and the data suggest that the objects delected by others. Note thai none of the complex contains point sources exactly at the OH objects appear to be larger thjn 0.! pc or 30 000 AU, position. In the last case no indication of any small and thai the lower limits lo the excitation parameters scale structure at the OH position was present and we conespond to stars earlier than Bl. Table I contains assume that, in fact, we have a non-detection of an four similar sources delected by others. A very likely OH maser which is projected, by chance, on a nearby candidate is also the |R source AFCRL # 809-2992, compact H 11 region. Since OH masers arc often situ which is probably a Type I OH maser |Moiris el al., ated so near to compact HII regions, chance projec as quoted by Merrill & Sailer, I974J and coincides tions are not unlikely. with a 4" radio continuum source [Wendker & Baars, This leaves nine pointlike (i.e. <3") continuum 19741. sources at the OH mascr positions and four non- In our fields, a total of thirteen OH masers were detections. As I said before, non-detections do not present. Seven are associated with poinl sources. tell us much; there could still be a pointlike source, What of the other six ? In three cases, we did not find only slightly smaller than the ones detected. How any continuum radiation from the sources, and we ever, in the literature there is at least one source obtained only an upper limit to the flux (Table 2). when non-detection is significant: OH 205.1 -14.1 However, these upper limits are not much smaller |Johansson et al., 1974]. Here the absence of a con than that of Hie weakest detected source. Therefore tinuum point source at 3 cm implies a diameter less r.on - detection leaves the possibility that a point than 180 AU, or at least one order of magnitude source exists which is only a few times smaller than smaller than the delected sources. This suggests those detected. In the three remaining crises we found strongly that OH 205.1 -14.1, althougli a normal an extended continuum source at the OH maser posi Type I OH maser, is really of a different kind. tion (Table 3). However, in two cases the angular Ull ft hAKMIiST EVOLUTION Ol H II REGIONS Table 2. OH mascn without a coincident continuum source on mascr Conlir luum source 6 cm flux Vanochtomatic Name 1 h Distance Reference density power (pel (millifluxui Ills) (erg s"1 Hi1 1 W33A 12.91 -0.26 < 12 4400 <3.5 xlO" 45.10 10.12 < 20 9700 < 22 x 10" W75S 81.7: *0.57 < 15 3000 < 1.6 x 10" Orion A 20X.99 -19.39 < 275 500 <0.8 x 10" (1) 205.1 -14.1 < 5 500 < 0.015x10" (2) References: ( I ) Upper limit for a radio continuum source derived from Webster & Altenhoft". 1970. (2) Upper limit for a radio continuum source derived from Johannson et al., 1974. Table 3. OH mascn coinciding with extended continuum sources Extended source 6 cm flux Observed source b density size (millifluxunils) (arcs) 19.61 -0.23 3300 Probably contains a point source of 1200 mfu at the OH position. 20.08 -0.13 110 Probably contains two point sources of 410 mfu and 250 mfu; the stronger one is at the OH position. 45.47 t0.13 2000 No indication of a point source at the OH position. 4. PROPERTIES OF THE SMALL CONTINUUM SOURCES 4.1 RADIO CONTINUUM SPECTRA nation. In all cases the object appears to have a spec trum increasing toward higher frequencies, although In only four cases do we have spectral infor- always with an index a < +2. In terms of bremsstrah- 132 H J HAHINl. lun£ models, llus implies thai we jte dealing with continuum source consists ol an optically itnn halo. sources becoming opticallv thin in the trequenO> providing most nt the ;i cm flux, plus a nucleus con- rangr studied The best example available in us iist sisttng ot ihe homogeneous sphere (Model a), dial fits DSI ihp Ai Note the line in Heme .' rcprcsewinc. J•i the higti-(teiiiiciH~) points ïlie second model I Model nn'Jel til The model (Model a> consists ot a homov c) assumes thai the source consists ol some nucleus, t-eneou" •.pheri' ot ionised gas with anpulai si/c I) and optically thin at tt cm. surrounded by an atmospheic central emission mcasuic h II has two tree parai- in which the electron density decrease* as ne , 4:iNrRARH>r'ROr fcRTllS tte arc a ware o) lUym and 2\)^m times Irom only two ot ihc objects in our Table I W3 Oil and (.111 M +0 7s nca[ NW 'MH. In bmli cases a rela tively strong IR source is present especially in the case of G 111.54 +0.7K. the slrength ot the IR source is surpnswi:. Kor the ratio S( Jt)yml'S((i cml wc find the value Sfl0(l. at least a factor 10 higher than for M 17 Tins same properly, exceptionally hiph values fur S(?0fm:f'S(acmr. ts also found tor other sources with diameters <0.3pc. Il owe this remark to Mi F.P Israel) An example is W 75 N [Wynn-Willums el al.. l*)74b|. However, not all small sources have this Figure 3. Spectrum of the compact radio source property. Clearly more near-infrared dala arc required. OS). Observations by Harris IIV74/ It seems to be of even more importance to find out show tliat at 6 cm, the diameter of the whether any correlation exists between the total IR source it tea than 1": the size at other tlux density as measured in the far IR and Ihe (> cm frequencies is unknown. Hu.x density. S CONCLUSIONS 1 (a) Compact H II regions have a tendency to cluster electron density, as nc rxi" . on several scale si^es: = 1 pc; = lOpc: * f>0 pc. ((e ) Compact H II regions smaller lhan 0.3 pc may lb) OH masers may coincide to within a few arc show an abnormally high value for the 20 ^m seconds with compact H II regions. However, an flux, when compared to the 6 cm flux. upper limit of 30 000 AU is indicated for ihe (( 0 At least one Type ( OH niaser is known (OH compact sources. To keep up the ionisation of the 205.1 -14.1) that is significantly different with radio sources, at least Bl stars are requited. respect to coincident H II regions: any continuum (c) No OH raasera have been found to coincide with source a) the OH position is al least 10 limes visible, compact HII regions such as K3-50. smaller than the smallest H II region detected so 6. A SPECULATIVE. QUALITATIVE MODEL The following qualitative model n« together alilll :'ie cocoon may break up and the inherence paths the ohscrvalium, and does nut seem lo contradicl aniy will be destroyed. Or. the cocoon moves away trom evidence. Probably it is not a unique way to represenit the star and the IR radiation field in the cocoon the observations, and certainly it is not completelly becomes much too diluted original (of the contribution at this Symposium biy It seems to mc that this qualitative sketch can he Dowries on If) CO emission), hui it is open for obserr- checked by many observations. For example, SITUL- vational lests, even in (lie neai future. tural studies of Type I OH masers with resolutions nf During the formation of a massive sta> IC-typcl,a Vt" m the IS cm lines will yield, when combined lOic/envclope system develops in the contractinig with radio continuum maps with 1" resolution, a cloud. The core will emit mainly infrared radiation. A detailed comparison nf the positions of the maser hot photospheic will form and ultimately (he UV points with respect to the ionised gas. Systematic OH luminosity from the photosphere will be able to ionn- surveys followed by radio continuum studies will lell ise the immediate surroundings leaving a cocoon nif us whether sources like OH 205.1 -14.1 form a neutral, dark matter outside the II II region. It is nuitt minority or a majority, and will tell us when in the obvious ihat the formation of the H II region begintss sequence of events during star birth the OH maser immediately after the photosphere has become ho:itt appears. Near and far infrared observations will yield enough, loi the formation of the H II region may bJCe insight into the total energies produced, thereby held up by dynamic effects, e.g. by 'false photoo- giving the luminosity of the central object)s). It seems spheres' |Kahn. 1M741 Now somewhere during thesse wotthwhde to detect silicate absorption bands around latei phases, i.e. after the core has become ho>tt 10/im. associated with the cocoons. Finally the ob- enough, a Type I OH mascr may appear, probabl|y jects should be searched for molecules, especially situated in the cocoon. The OH maser lasts until thie those Indicative of high densities (HCN. CS the higher IIII region expands too far (say. beyond 11> 000 AUJ) ) lines! and, perhaps. 6 cm emission of HjCOfcf. the and destroys the masenng conditions. For examplee. contribution by Dowries at this Symposium). 7. ACKNOWLEDGEMENTS The Westerbork Synthesis Radio Telescope is berg and H.E. Matthews for their collaboration in operated by the Netherlands Foundation for Radio obtaining the data and for giving me a free hand in Astronomy, with financial support from the Netherr- discussing them here. I would tike to thank F. Israel, lands Organisation for the Advancement of Pure F. Kahn and F. Olnon for useful discussions. Research fZWO). I must thank W.M. Goss, A.Winn- REFERENCES 1. Albada, T.S. van. Bull. Astr. Insr. Neih. 20, 47 6. Harris, S., Monthly Notices Roy. Am. Soc. 166, (1968). (1974). 2. Baldwin, J.I-., Harris, C.S. & Ryle. M-, Nature. 7. Hughes. V.A. & Butler, R., Aszrophys. J. 155, Pftys.Sci. 241,38(1973). 1061(1969). 3. Blaauw, A., Ann, Rev. Astron. Astrophvs. 2, 213 8. Israel, F.P.. Habing, HJ.& de Jong, T., Astron. K PtnkauL Keidel Publishing Company. lïnid- li Schraml. J S. Mezger. P.G.. Asirnphn J. 156. rccht. p. 235. iy"-l- :wiifhii 12. Martin. A H. Monthly Xi-turt fi.'\ Astnii .W 20. Turner B.I'.. J fto.v Aunm. Soc.Can. 64. 221 157.31 ll«»":i. |l°70). 13. Martin. A.H.. Monthly Xoticcs Hot: Astron Soc. 21. Wcndkei. HJ. & Bans. J.W.M.. Astro». A Astro- 163. I41<|i73| phys.. in press. 14 Matthews. H.l-.. (.»««. W M.. Wmnberg. A- & 22. Wmk. J>;.. Allcnhoff. W.J. &. Webster. WJ. ftibinp. H.J.. AUron. DISCUSSION K.W- MICHtL: I>r. Habmg's study has obviously tainly sufficienl. They may not have been a few years given extremely valuable information on Uic topology ago. and morphology o( some OH masers. This might be a baiis for developing realistic constraints on the excita MARIE-CLAIRE LORTLT: Do we know the OH tion mechanism of the Oil maser. Have attempts been profile uf OH205.I-I4.I which is located in a T asso made in this direction? ciation neat the reflection nebula NCC 2068? Secondly, which OH sources do you place among the HJ. HABINC: Not yet. but we hope that they unclassified OH sources; the broad-line one OH 07 will cmerg; when mure similar sources have been 34-14 = OH231.8+4.2 discovered by Turner? found and better information about the radio spectra is obtained. Infrared data are most urgently required. HJ. HABING: The maser is a main-line. Type I maser. A spectrum will be published in the 1 May B. HA LICK: Oil sources have not brtn identified 1974 issue of ApJ-, by Johannsun et al. wiiii continuum sources near bright H II regions. Do The source you mention I would like to call un- you feel thai this is a real effect, or that these con classifiablc. There arc a few more such sources, (-'or tinuum sources have not been detected because of reasons of convenience, I would also put the Type Na their proximity to bright Hnc structure in the nebula masers in this category, because there are so few of and the limned dynamic range of radio synthesis in them and no hod y can make much sense of ihem. struments? V. PLTROSIAN: h is important to determine the HJ. HAB1NG: 1 think that previously aperture infrared luminosity of these sources because as men synthesis instruments did not have the capabilities to tioned, assuming no infrared radiation, the ionising detect the sources. The problem is thai you need a star is earlier than 09. If so neither the ultraviolet nor reasonably Urge field of view, a high sensitivity and a infrared pumping mechanisms could be in operation good dynamic range. Present-day techniques are cer- here. 135 AN EMPIRICAL MODEL FOR THE STRUCTURE OF THE ORION NEBULA Bruce Balkk Lick Observatory Board of Studies in Astronomy and Astrophysics. University of California. Santa Cruz, USA R.H. Gammon & R.M. Hjellming National Radio Astronomy Observatory". Charlottesville, Virginia. USA ABSTRACT An empirical model of the Orion nebula is pur density gas to the core. The gas freely expands in the posed whereby a high-density 'core of ionised gas sur other directions where possible through fragments of rounding the exciting star 0X C is partially imbedded the original neutral complex producing an extended on the near side of a massive neutral complex. Radi region of tenuous, 'swirling' nebulosity. It is shown ation from 01 C continually ionises the dense neutral thai such a model can explain the large amount of gas, and a network of (lows from behind the star and information pertaining to the spatial and kinematic from the north and east result; these resupply high- structure of this well-studied nebula. I. INTRODUCTION A detailed understanding of one HII region somewhat ad hoc synthesis of the old concepts with would be an important key to the understanding of new ideas suggested by recent experiments. all H II regions. In this paper we shall investigate the There is no single experiment or set of experi detailed structure of the Orion nebula. Certain as ments that directly suggest the model, so the discus pects of the model have been suggested previously by sion begins with a presentation of the most relevant Wurm [1961). Kaplan & Pikelner [19701,Terzian & data. Many interesting results and the references for Balick 11973J, and Zuckerman [19731. We shall others will be omitted in the interest of brevity. We present the relevant concepts in the course of the shall then develop the model and theoretically elabo discussion and synthesise and refute them in order to rate on some of the concepts behind it. Finally, we construct a detailed model of the nebula which can will briefly explore the possibility that important be used as a framework for interpreting the multi aspects of this model are applicable to other H II farious observations of this well-studied HII region. regions. The model is best described as a semi-empirical and * Operated by Associated Universities Inc., under contract to the National Science Foundation. B H-MKK K 11 (-AMMONAHM MJI t I.MlNt; :. BACKGROUND The H 11 tesion (hion A i> lo.'aïed m a large com standing ol the nebula mote than it lui helped it plex ni neutul clouds, stellai associations, iclleciioii A map i*t the coiilinuun- tadio isnplmics observed «ehube. jnJ oiiin H II itpnns extending ovet a al A 1.15 cm is shiiwn supentnpoved on an optical 10" \ 10*' region -.hnwît m I ipuic 1. Otinn A is in the photogtaph ol O11011 A I" hipure -, which has hecn southern pan ol [his complex jrni consists ni the taken t'10111 Schiaiiit & Me/]jci jl'Xt'M IICCJUSC llic> hriphi nebula WT alone, with iho smailei nebuU ate nol atlecled h> nbscutalion. the h tightness mi- SU:-. v.hkh lies about !U 10 tlic M: ol M4_\ Al both photcs provide a good indicjlion ol the deiisiU disin- opik-jl jnd ladin frequencies. Onnn A is 011c ol ibf hution ( ptniecled on the plane of the sk> t on a stale bn^iileM. jnJ thus best studied, ni" ail ionised nebu sue of lhe beam width a! titqiicncies wheie lite tailtt* lae ImmcalK. the large aninum nt data -mailable lui npucal depih is small. With lesnlutiotis ol H' as in this nehuia often seems in complicate oui undet- Figure 2. the densuy distiibulion appeals lelativelv Figure I. A photograph of the Orion region in the tight of Ha covering an area about 10° x 10°. Super imposed on the photograph are lovrresolution radio continuum isophotes as measured by Rishbeth fl9S8] at a wavelength of 3Jm. Orion A is coincident with the brightest radio continuum emission. Other features include NGC1973-5-7 adjacent to Orion A to the north, the Horse head nebula (about 3° northeast of Orion A). Orion B (about 4° northeast of Orion A), and "s Loop (about 3° east of Orion A along the ridge of radio emission/. I-MMRK Al. MOptL I OK STRUCTUHf. Oh ORION NhHL'LA 137 simple, consisting of an inner Gaussian core of width . of Orion A taken with the 4 m May al I telescope al 3* or 4' (O.S pc) centred very close to the trapezium Kitt Peak National Observatory in the light of [S []] and an extended 'plateau' which extends for 10' from X 6717-6731 A Icourtesy of T.R. Gull). The core ihe cenire. except tu the SW. From radio observa region is the dark area near the centre of the photo tions at many frequencies, it is clear that the inner graph. The brightest optical nebulosity is found in the Gaussian core becomes optically thick at radio fre western parts of the core. The prominent "dark bay", quencies of less than I or 2 GHz. optical filament or 'bar', dark lane, and M43 are indi Higher spalial resolution radio synthesis observa cated schematically in the figure (many of these same tions {I'ig.3)show that higher density fine structure is features can also be seen in Figs. 2 and 3|. On larger superimposed on the core. The observations shown scale sizes, the optical nebula looks similar to the here have been taken from Webster & Alienhoff radio map except for the dark bay and lane. [I970] and were made al 2.7 GHz (II cm). These Located at the centre of the core are the four so- s J 'condensations* have densities of J0* cm" (or called 'trapezium' stars. The southernmost of these : ghcr if optical depth effects arc importanij and are 01 C, is an 06 star thought to provide all of the ultra distributed within a 30" region centred near ihe tra violet excitation for M42. pezium cluster of stars and the brighest optical nebu The density and the temperature of ihe core losity. There is a close coincidence between the region and environs have been determined in many dif brightest radio and optical structure just west of the ferent ways. More recent observations of higher accu trapezium. racy have shown very good agreement in the results. Optically, structure can be found with all scale Perhaps the most direct measurement of the density sixes. In Figure 4 we show a high-quality photograph , comes from the ratios of forbidden line intensities Figure 2. The radio continuum isophotes of Orion A at\ 1.95 cm, taken from Schraml £ Mezger {1969] and used with permission. The spatial resolution is Ï. ». BAUCK. R.H. GAMMON â R.M. IUELUUNG Figure 3. The radio continuum synthesis mop of Orion A at XJI.lcm, taken from Webster & Aitenhoff {I970J and modified for display with permission. The hatf power dimensions of the synthesised beam are 7" x 30". The cross, triangle, and square indicate the position of the radio continuum peak, Kleinman-low infrared nebula, and the Becklin-Neugebauer infrared point source, respectively. I MI'IRK AI. MODI L lOR STHt'C'fURI- Ol ORION NHULA measured opucally. Pie iesuEi\ depend «n the ionised species sludicd In some degree, hut values on ihc nfdei of II)4 cm'J are typical of the bright regions of the core I strung variations are also observed locally). The- gross proper lies nf the optically determined den '•WF sity distribution ague with the radio continuum results, except that the optical distribution is some what more peaked. The densities have also been studied using radio recombination lines measured at many frequencies. Results consistent with the other methods arc nnw being obtained. Some clumping along the line nl sight seems In be implied. lemperaiurcs measured by several different methods all give consistent resulls close in 10* K in ihc core region, F.nhanccmciil of the lemperature by about 20- seems indicaicd by recent optical line studies m the outer regions about 10' from ihe core. In sharp contrasi to the relatively simple picture implied by the density distribution is the picture indi cated hy the velocity distribution. Kincmatically. the core is very active and shows a wide range of veloci ties as a lunclion of both position and line excilalion. Radio recombination line maps show a gradient of velocities from about 5 km/s in the S\V to 8 km/s in the NF. near M43. The lines are all surprisingly well titled hy Gaussian profiles, at least ai frequencies where the beam width: arc less than the core di mensions and the line widths are nearly constant. Optical sludics of the kinematics have the advan tage of higher spatial resolution and show that much kinematic structure exists on small scales. Une spin- lings and rapid variations of the velocity are common A high quality photograph of Orion A place. Each forbidden line studied shows a somewhat taken with the Mayall 4 m telescope in different kinematic picture, and in at leasl one direc- the tight of l S ill \ 6717-6731 \ (cour lion the line velocity is seen to be a function of the tesy T.R. Gull and the Kin Peak Sational ionisation potential for species formation. This is Observatory). Tiie positions of importât" illustrated in Figure 5. which was adopted from Kaler features are indicated schematically. |l%7j and updated where possible. Vic observed velocities of optical lines in llie brightest optical nebulosity are plot ted as a function of the minimum photon energy required to produce the ionised species/adopted from Kaler, 1967}. The velocity of carbon monoxide is indicated on the velocity axis. Optical hydrogen and helium lines have not been included because their line sliapes are known to he complex. Vie H, He, and C velocities are from radio recombination line measure ments. Vie mean velocity of stars in the Orion cluster and the velocities of the .„ s r trapezium stars alone are shown on the right. Also sketched is the average \2I cm emission profile within JO' of the Orion nebula. B BALK K, HI) GAMMON ARM. HJH LM1N0 i. THE MODEL The basic geometry ol" the model we propose is shown in Figure n. A 'core' IIII region surrounding the exciting star tf'C o actually an ionised cavuy whiL-h is partially imbedded on the near side of a large neutral complex thai contains (he molecular clouds and infrared sources in its interior. Relatively undi luted ultraviolet radiation falls on the dense neutral pas to the E_ N, and rear of the cavity thereby tre ating newly ionised gas which is seen as the bright MTUdure in the radii» maps. The densities in this region range upwards of 10* cm1 whereas in the outer regions the density is much less. Su that two processes are likely to be important. First, ihe density gradients drive the gas out of the core region towards the south, west and front (free expansion) on a lime scale ut'about 10* * years. Second, gas is [«supplied In the core fiom the boundaries through a system of 'flows', whose nature is discussed below. The flow pattern depends on details of the cere geometry which are not well known at present: however, we show next thai certain properties of the geometry' can be ascertained by a careful analysis of Ihe observed kinematic structure. Inside the core there is apparently a high-density Figure 6. A schematic of Orion A sliowing the flow primary flow which corresponds to the brightest opti pattern. The lower portion of the figure cal and radio structure located just west of the trape represents a cross-section through the zium. The placement of the primaiy flow in the plane nebular centre in the cast-west direction of the sky suggests the gas motion is directed nearly along the line of sight. The star in the along the line of sight; indeed, the difference between lower portion is d'C. the cross-hatched the llli line velocity and the velocities of species area is the region of Cil emission, and found adjacent to the nebula (i.e. C+. l.P. = 11.4 eV) the dot pattern indicates probable density suggest that the flow has a component of motion fluctuations in the neutral gas. along the line of sight which is nearly sonic and direc ted towards the Earth. The flow model can therefore explain the run of velocities shown in Figure 5, since velocity, especially at the northeast edge of the cavj. species of intermediate ionisation potential such as ty; this is indeed observed. This interpretation of the + + 0 and N are found in the ionisation front between H II velocity gradient is preferable to that of a rota the neutral region where the C II lines are formed and ting core, which has been suggested in the "ist, since ++ 1 the interior H 11 region where 0 , Ne"*""", and most a routing model predicts an H U-C II vcloci. diffe + of the H is found. Here we are assuming that the rence which is lirgest at the edge of the cavity and flow is optically thin to -visible light; convincing evi smallest at the centre, whereas the opposite is ob dence for this assumption can be found in the litera served. ture. There is not sufficient time to review the ade Other flows of lesser density exist elsewhere along quacy of the model for explaining Ihe large amount the neutral boundary, particularly to the north and of experimental information available on Orion A. To east. Because their velocities are probably smaller the best of our knowledge, the only data thai lie than thzt of the primary flow and have less of a pro beyond the scope of the model arc the observations jection along the brie of sight, the H II line velocity in of supersonic line splittings which are a matter of these regions can be expected to approach the C H some experimental controversy at the present time. I MPIRlCAl WODU HW STRVCTIM Of ORION NI BLIA 141 4. THEORY Mieinetical justification lui some aspects »t ihe sities 3rc quite large, so thai U is likely that the model is possible. We now pursue ihc tlienry ot the neuiial region behind Ihe tlow » small; the observed [lows, and discuss some of tile resulting prédit lions. si« of the primary How. < 0 1 pc is ,.1 insistent with Ac shall use N. v, and T to represent the number I Ins. picture. Weaker flows will originate elsewhere in denMty. velocity, and temperature, respectively, in ihe ca*U>, whvrcver the neutre density exceed:, I In- ionised ( H II) and neuiral ill II regions. ahoui Hi' tni J. these will he %ubsonk MiK'h ol tlic theory has been developed by The rnaiMiillow rate to the Lore. Ml M 111. i, iin-i, Mendis |]l»iyi| and Dysnn | J0"7_1 J whu considered a •>> M - m N(H II) *1H H) A. where m is the average hypothetical '«et ni t "miliums oniy slight!} d! 'Went mass pet paiticle — 1.4 rime*, ihe proton masi jr.J \ !rom those "I ihe presenl model lo summarise, the is the cross-sectional area ot ihe flow - Id" .m: Hows originate m the ionisation I routs ot the critical Substituting the measured values ol S jiid \. ne tmo or strong 0 type tm cxciiiug stars as early as fl'f. M~ lir4 M^y"' Olher flows will hase j oimpjra'nle am' the flow velocity v.ill he in the range Ml - etfect furlhcrmore. since the mass ot ionised gai 11 'II kni.'s The exact flow patlcrn depends on delails Orion is measured to be - 10 MQ and the relaKatif ill Ihc local geometry, the stellar radiation intensity, lime is - I04-5 y. we see thai this mass inflow rate and ihe densitv of gas in Iront of llie flow. Under the capable of sustaining the observed densily disirr expected conditions it can be shown thai NUI I)' lion in equilibrium. The mass of the neuiral com;- x S(JIII) - 4TIH ID/101 II. Molecular and Til line is about Iff" MQ based on molecular line observa reservations indicate thai TIN I) -10'"SK. and tions, so that clearly ihe mass inflow can be ne ïtlî II) and N(H II) can be laken In he I04 K and lived, and the compact core of Orion may f1 der ID4'' cm"', respectively, so that we derive N(H II — than estimates based on ils relaxation time iirr 101 * cm'1 adjacent to the primary flow. Such den- 5. FLOWS IN OTHER HI REGIONS The possibility thai flows may be important in fine siructure. It is, of course, possible t" it the proio- nllier H II regions is suggested by the many morpho stellar model explains much of the obs ved structure logical similarities between Orion A and the other elsewhere, but unfortunately this nodei cannot nebulae. Line and continuum observations of bright account- fur the dynamic propertie jommon to all H H regions wilh compact cores show evidence of brigiit nebulae. Consequently, we feel that flows strong kinematic aciiivity, systematic H 11 -CM should also be expected to be a common occurrence velocity differences, nearby dense molecular regions, in these H II regions, and we cauuoii that the flows interferometer fine structure centrally located within may have been overlooked, pe iap; because their the compact core, and similar excitations and size brightness is smaller than tha of the protosteliar scales; in short, alt the necessary conditions for flows nebulae. seem tu exist in these compact nebulae. In support of the dual fiow-protostellar nebula Several models have been proposed to explain the hypothesis we offer the folio-.ing scenario. As a clus density structure seen in H II regions. The mosi popu ter of stars begins to conden .• in a large neutral com lar of these is the idea that the condensations are plex, it is well known that ihe more massive earlier small dense H II regions associated with protostellar lype stars evolve fastest. ** ere is undoubtedly some cocoons which are in the process of collapsing. One period in their evolution "-vhere protostellar nebulae reason given in support of this hypothesis as opposed are formed around the p >re massive stars, but event to ihc flows is thai bright small-diameter infrared ually Ihese stars emerge from their 'cocoons' and sources are often coincident with the bright radio begin to ionise a larger region containing other proto- siructure, implying thai local dust is being heated by slellar clouds as well as 3 lower density background. resonantly scattered Lyman alpha emission from the Bright ionised jackets, that is flows, will form on the prntostellar nebula. Such ail argument is fairly reason outside of the protostellar clouds nearest the exciting able; however, we nole that in Orion A no such small stars; these flows may be capable of absorbing a large diameter infrared emission is found within 1 ' of the fraction of the ultraviolet flux from Ihe star, as re- H BAIICK. HH IIAMUDN 1 RM HltLl-MINt; quired b> the obseived radio fluxes. L.sidr the latper irlation of the fine structure with the centres of the puwostcîlai clouds arc 'he infrared sources awnciaied compact cores. AJso. one is able to understand the with stars collapsing in the interior. The radin émis longevity of the compact cores, since new high den- sion from the flou will appear very close to the intra- Miy material is icsupplied by the flows ai Icau until red source even though they are not physically asso the nearby clouds ate dcstioyed. The model can he ciated . lested bv careful comparison of the radio and infra The principal advantage of this picluic is that it red positions and by hiph spalial resolution recom explains both the dynamic activm as well as the coi- bination line maps. REFERENCES I. Dyson. J.E.. Asmm. & Asinrptira 2~. 45" 6. Jcman, Y. A Balick. B . in Fundamental* ol Cm- (1973). mic Physics. Ed A.G.W. Cameron 4ti» be publis Kaler.J.B. Aarophys. J. 148. 9?5 (191.7). hed). Kaplan. S..A. & Pikelner. S.B-. The Intersieltoi Webster, W.J. & Altcnboff. W-, Aun>phys. Isti. Medium. Harvard University Press. Cambridge, 5.::? (1970). Mass. pp. 147-9. 1970. Wuim.K.Z. f. Asnvphyi. S2. 14*Ml H.M. JOHNSON: By 'cavity', do you mean that dust along uitli it. Questions of dust evolution aside the Trapezium and ionised gas really exist in a less one would expect the dust density to be piuportional dense part of the nebula compared with the surround to the gas density everywhere. ing neutral gas? A. PEDUAR: Your model fur C II < B. BALICK: Ves. ta fact one embarrassmenl of fers from that proposed by Dupree. elc. Could you this model is that the densities required for the neut comment on this? In particular, how you explain the ral gas adjacent to the bright primary flow are of the high intensities of the car lion without slimulated order uf I07cm"3 or so. Once the gas is io used, the emission? density drops to the observed value of 10*-i cm"1 (the perfect gas bw can be assumed to show this). B. BALICK: The problem of the C II emission is a Then the gas density drops to 101 cm"3 or so outside complex and controversial one at present. In a paper the core as the gas freely expands to the front, south by R.H. Gammon, LH. Doherty, and myself ( 15 Feb. and west. 1974. Ap. J.), we discuss the C II distribution and emission in Orion A. Dupree may have been some H.M. JOHNSON: By speaking of dust 'wrapping what misled by Iter geometric assumptions, and it around' the ionised gas, do you mean the dust is not appears that stimulated carbon emission (at — fakm/s) mixed in with the ionised gas? If it were mixed do we dominates for lines with n > 100, whereas spontane have any idea why the dust is not distributed as ous emission (at — 10 km/s) dominates at higher fre smoothly as the continuum (BremsstrahfungJ maps quencies. We plan to observe C39a lines later this suggest the ionised gas to be distributed? year to investigate this problem further. B. BALICK: 1 thinK the dust and gas densities are M.V. PENSTON: Is the time of 10" years the highest in the neutral complex. As newly ionised gas time since the Trapezium switched on or simply the enters the core it probably brings a fresh supply of expansion time scale? I-.MPIRICAI. MODKI. lOR STRt.XTURK OI- ORION SKbLLA 143 B BAIJCK: Trie latter. Incidenlally, the age of nf technical prohlems {discovered later) m the equip- llie Trapezium once estimated by proper moljun ment, studies to he 104 years has been withdrawn because 2. H II REGIONS IN EXTERNAL GALAXIES 145 NUCLEI AND H II REGIONS IN SPIRAL GALAXIES: PRELIMINARY RESULTS FOR M iOI P. Benvenuti & S. D'Odorico Asiago Astrophyskal Observatory, Padova University. Italy The relative intensities of the emission lines Ha, the nucleus is revealed. Physical conditions and N/S X6584 of [NH|, XX 6717, 6731 of [S II} for the abundance ratio in H II regions are very close io ihos;; nucleus and 10 H II regions of M 101 are given. From obtained for M 33. An upper limit of4x Iff-6 erg 3 1 1 -1 the [SII) lines ratio it is found thai Nc = 3000 cm' cm" s" arc s for the surface brightness of the inter- 3 in the nucleus, while Nc is less than 1000 cm' in the arm area of M 101 is established. H II regions. The presence of a peculiar structure in . INTRODUCTION This work is pari of an observational programme, measure), we are able in discuss the possible ionisa in progress at the Asiago Astrophysical Observatory, tion mechanisms; (iii) moiphological properties and concerning bright, face-on, spiral galaxies. So far, line emissions of the nuclei. M 33, M SI and M 101 have been observed. Willi this The spectroscopic observations were carried out investigation we want to study: (i) the chemical abun with the Asiago grating spectrograph [Benvenuti ct dance and the electron densities in the H II regions of al., I974|, attached to the 122 cm reflector. Direct these galaxies. These data are correlated with the dis plates of the galaxies were obtained with the new tance from the nucleus and compared with galactic 182 cm reflector •Copernicus' of M-Ekar. The scale values: (ii) interarm emission. Several authors [Dehar- on the plate is 12"/mm,which allows good resolution. veng & Pellet, 1970; Monnet,197I; Comte, I973; In the near future a new spectrograph will be opera Benvenuti et al., 1973) have pointed out the pres ting at this telescope and we expect to use it to study ence, in some face-on spiral gahxtes,of a faint diffuse the details of the velocity field in the nuclear regions. emission coming from the interarm area and no! as The results for M 33 have already been published sociated with distinct H II regions. By measuring for JBenvenuti et al-, 1973J. Here we present preliminary this region the line intensities and the EM (emission data on the nucleus and some H II regions of M 101. 2. THE NUCLEAR REGION Figure 1c shows the central region of M 101. The (less than 1 ) enabled us to resolve a peculiar micro- photograph was obtained in blue light (103a-O + spiral structure in the nucleus. Two knots, or stars. GG13) with the 132 cm reflector. The good seeing are connected with the central condensation and I'. Ill NVI Mil A !i HUDORUtl HA X6584 M 33 -1 r- t* Night Sky M 51 I I •i'in,' \*mii>mt*mmmlË*mm*ÊmmmmÊ* i 45" . 4300 pc M 101 ^.W*m*i»imm**m.**!*ÙÇH**V <'<-***'> •» m fi» , -< t 1700pc | Blue photographs and spectra of the nuclei of M 33, M 51 and M101. The direct plates were obtained with the 182 cm telescope (original scale: 12"/mm). Scale in parsec according to the distances in Table I. form a hind of spiral am?. A more extended arm to optica! centre [Allen, quoled by van der Kruii, the north is also visible. The whole structure is abom 1973]. Because of the peculiar optical structure, we 10" in diameter (350 pc at an assumed distance of think that a high resolution radio map would be of 7.2 Mpc). The central condensation and the section great interest. A kinematic study is not available. of the northern arm close to the centre appear stron The nuclei of M 33 and M SI are also shown in ger on a ted plate. Figure 1. The properties of the nucleus of M 33 have A weak radio source is F:-BCM in the nucleus of been discussed by Benvenuti el al. [1973]. The nu M101, and is apparently displaced from the cleus of M 51 is one of the brightest at 1415 MHz NUCLI-I 4 H II KI-.filONSIN SPIRAL (iAt AXII S among imrmal galaxies |van der Kruit. 1973|. Expan ratio of the sulphur lines 1(67I7|/I(673I ). Hie low sion motions arc present in the central region and high density limits of this ratio are 1-5 jnd 0.4 IBurbidge & Burbidge, 14641. In a blue plate The density is relatively high in the nucleus ni M 1 Ul I182 cm telescope, courtesy of R. Stagni) the stellar (about 3000). Tins value is close lu that lound in the nucleus of M 51 appears cmh'ilded in an ellipsoidal nucleus of M 81. Our result lur the 7" aperture in hulge(25"x40") of lower brightness; several siarlikc M 51 gives a higher demi I y than thai measured h\ images are visible. Heavy absorption lanes border Ihis Warner [19731 through a smaller aperture IN = region and short spiral arms originate from it. These 3000 cm"3 against 1000). Since the densit> i\ usualk spiral aims can be followed apparently all the way to found to be highest in the innermost region ni a nu the nucleus. cleus, new observations are needed in continu the Vic have obtained seven speilra through the nu r versed trend we observe in M 51. Then' ib also J cleus of M 101 and five through the nucleus of M 51. discrepancy between our value ot the ratio \\a, |S II| The spectra cover the region near Ha at 125 A/mm. 2: 1 and Warner's 119731 value, whit h is aboui 3 Our f Unfortunately, with the present equipment we are value is cl • to that observed by Peimhen [1M6HJ not able to resolve in the spectra the structures seen Low va of the Ha/6584 ratio ha%e been mea •n the direel plates. Our spatial resolution is about 6'. sured in ihe nuclei of some galaxies, among them The emission lines of Ha, X 6549 and ^ 6584 of M 51, M 64 and M 81. Many authors have discussed |NII|. X67I7 and X6731 of |SII| arc observed in the possible explanations (see V'trner. 1973. (or the ihc nuclei. The emission line strengths arc computed most recent discussion). It is not yet clear whether as described by Bcnvcnutict al. 1197.1 J. the low ratio is due to nitrogen overabundance ur tn peculiar physical conditions in the nuclei, the first Table I summarises the results and compares hypothesis being the most probable. In M 101 we them with the available observations of other normal measure a value of 2.35 for the ratio: this is similar to spirals. The dista ;es and the radio fluxes are by van that found in an intermediate excitation H 11 region. der Kruit (1973). The values for M 101 are referred There is no indication from the spectra thai the ratio to a 14" circular aperture. An average value for the might be smaller in the innermost region of the nu intensities was computed from all spectra because no cleus. Deharveng & Pellet J19701 found Ha'fi584 = change with position angle was observed. 1.8 up to 5" from the centre. This value is smaller A detailed analysis of the physical conditions and than ours, but the difference may well stem from relative abundances will be given in a forthcoming observational uncertainty. The estimated error in our paper. Here we discuss briefly two points. It is known measurement is 15%. that the electron density can be derived from the Table 1. Emission line strengths in the nuclei of spiral galaxies Hubble D»lmcr ''(.'il tfa'IStll lypf iMpcl ili.D'Oiluniv&Pi-in inns closer lhan <»0" I P. BfcNVKNim 4 S H ODORICO For the galaxies listed in Table I. the Ha/6$84 vide a clue to the interpretation of nitrogen emission ratio is correlated with the radio luminosity of the sirength. For this purpose more observations of nuclei at 141$ MHz. The (NHJ X6S84 emission is ettitssion-lifie intensities at high spatial resolution in stronger in the more acme nuclei. This relation de the nuclei of spiral galaxies are needed. serves further study because it might eventually pro 3. H n REGIONS AND INTERARM EMISSION We have obtained 12 spectra across M 101. The umn 2. Column 3 gives the distances from the nucleus nucleus or a reference star were used to set the slit of in the plane of the galaxy, assuming an inclination to the spectrograph on the HII regions. All the emission the line of sight of 63°, a position angle of the major features seen in the spectra were identified with easily axis of 30°, and a distance of 7.2 Mpc. The three last visible individual H 11 regions. These are indicated in columns report the line intensity ratios. Figure 2. Table 2 summarises the line intensities for The l(Ha)/I(6SS4) and l(Ha)/I|S 111 ratios of the the observed regions. Five of them were also observed observed regions are very close to those obtained in by Searte [I97I|: his numbering is reported in col M 33. As in that case, a strong correlation exists Figure 2. A photograph of M101. Regions studied in this paper are numbered according to their distance from the centre. Positions where a limit far the mterarm emission was measured are indicated by rectangles. NUCLEI A H II REGIONS IN SNRAt GALAXIES TiMe2 DBUI.CC from Region SeaileNo. the nucleus KHa)/K6584) l(Ha)/ip>II| I(67I7)/K673I) (kpc) i i.S < 3.58 < 2.52 2 2 3.6 2.23 1.59 3 5.3 3.01 2.53 1.06 4 3 6.0 1-57 3.31 5 6.3 2.90 2.22 1.41 6 5 7.2 1.98 > 2.17 7 7(NGC5461) 10.4 > 3.34 > 2.51 1.31 8 1)1 < 2.85 > 1.60 9 - !2.l 1.82 > 1.67 10 10(NGC5455) 14.2 > 4.41 > 2.96 1.36 between 1<6SS4) znd i(&7i7-t*?3l). This is shown in Figure J by the plot of IogI(6$84yi(Ha) vs. log I •a* (6717+673i)/I(Ha) for all the observed regions in 1*1*51 1 (Ha) M 33 and M 101. This supports the lea that the •03 jN II| and |S \l\ lines originate in the same vciume element and that N(N+)/N obtain a limiting value lor the surface brightness, we uppet limit of 4x Iff"" erg cm V .res"' for the measured some intensity profiles, along the Ha emis in (era riu emission. This is clcarK neb lower titan sion, usine Sea i le's region no. 2 as a calibration, Foi the value found in M 33. sugges' m tliat the physical this icgion he gives ihc absolute flux at !tji and the conditions in the inierarm me- .ium of the two galax llHal/t(H£) raiio. From these data we derive an ies ate quite different. REFERENCES 1 Benvenuti. P.. IVOdorico. S. & Peimbert. M.. 6. Monnet, (1.. Asiron. & Aitrophys. 12. 57*» Astron. dt Astroptiyi. 2H. 447 ( J97.Î). (1*71). '. iknvenuti. p.. Capacciolo. M. & D'Odorico, S.. 1- Peimbeil. M., Auniphyn. J. 154. 3.1 < 1968). Mem. S.A.Il.. in press. 8. Scarle. L. Asirophys. / 168, 3:7 < 1971 ). 3. Burbidge. E.M. & Burbidge. G.R.. Ar.rophys. J. 9. Van dcr Kniit. P.C., Astnin. A Ajiropliys. 29. 140. 1445(1964). 263(197.?}. 4. Comte. G.. Thesis. Université de Provence. 1973. 10. Warner, iy/..-isirophys. / 186. 21 (19731. 5 Deharveng. J.M. & Pellet. A.. Asiroti Ji Astro- pkys. 9. 181(1970). HJ. HABlNG/tt. JAFFE. We think we recall that Ila/|KI1J ratio. MS I and M51 have nonthermal nuclei, as judged from the radio data, whereas M33 and MI01 do not. It P. BENVENUT1: I agree, but 1 think that further would be very interesting if a correlation existed be observations of a more complete sample of nuclei are tween the presence of a nonthermal nucleus and the needed to decide if this correlation really exists. OBSERVATIONS OF THE DWARF GALAXY AND H 11 REGION IIZW40 W. Jaffc*. G.C. Perola** & M. Tarenghi** ABSTRACT New radio observa I inns of M Zw 40 made with that the dust is concentrated in small regions each ihc Westerbork telescope at 21 and 6 cm will be with optical depth 1 in the ultraviolet. For a given presented. These show a point source at the position number of such regions N. we can find the radui>. of the H II region seen by Sarg':M & Searle. density, and mass of the regions as a function ot V Dr. Tarenghi reporls a new 20 pm measurement of The dust-lo-gas mass ratio in the H II areas turns out this object by Dr. Rieke. to be about 10"saN , where a is the grain diameter Assuming ihat the infrared radiation comes from in microns. Since N is less than about 10s. the num dust with emissivity equal to O.I(X/5pmjJ, we find ber of bright stars in the galaxy, for a = 0.1 fim we colour temperatures of 200 K and 150 K for j=0 and find a dust-to-gas ratio of about S x 10~4. or abnut 2. From these temperatures we calculate the dust 20 times lower than that in the solar neighbourhood. mass for the two cases. If uniformly distributed over We think thai this low value is probably linked to the the core region of the galaxy, this dust would be youngness of the system. optically thin in the ultraviolet. Instead, we assume DISCUSSION H.M. JOHNSON: Would you make a comparison posite spectrum and can say nothing about individual of this object with 30 Doradus in the Large Magel stars. lanic Cloud? Stellar content? Wolf-Rayet stars, for example. K.W. MICHEL: Your method of evaluating the dust mass will give you only that component which is W. JAFFE: The «^ectra taken by Sargent and at 200 K, and not the colder dust, which might be Searle show this object to be similar to 30 Doradus more abundant. Does this explain the discrepancy of although with perhaps 10 times as many young stars. your dust-to-gas ratio as compared to the interstellar The stellar continuum is very blue indicating an over value? abundance of young relative to old stars as compared to the Galaxy or even the Magellanic Clouds. Because W. )£ vrE: There may indeed be a cooler com the object is small (3"x 5") we can see only the com- ponent, but we do not expect its luminosity to be higher than that of the 200 K component, since this • Sterrewacht, Leiden. The Netherlands. is already near the total UV continuum luminosity of ** Istituto di Fisica & Laboratorio di Fiaca Cos mica, Milan the stars involved. In this case the observational con Italy. straints give a dust-to-gas mass ratio which depends 152 W. JAFl-i; C.C. PEROU « M. TARKNC1U only on T~\ so that a 100 K dust temperature would W. MFFE: The near agreement of our 5 GHz not change OUT conclusions. flux and the mix predicted from the H0 measure ments of Sargent and Searic on (he basis of thermal V. PETROS1AN: If most o( the radio continuum emission from an IIII region convinces us that we is non-thermal, then the dust-to-gas ratio would be have not grossly overestimated the thermal compo larger. nent of the radiation. 3. DUST IN H II REGIONS EVOLUTIONARY CHARACTERISTICS OF A BIMOIML GRAIN MODEL* J. Mayo Gmnbcrg & Seung Soo Hong Stale University i*f New York ai Albany and Dudley Obsenarory ABSTRACT A birmxia) model of interstellar grains consisting at the other end of star formation into youns H II of (i) silicate cores of size — 0.06 ym with modified regions. Physical justification is presented to srmw ice mantles of - 0.1 ftm and (ii) very small particles thai not only in dense clouds must one expect the of silicate and/or graphite of size - 0.005 ^m is fol core-mantle grains to be larger than normal, but also lowed through various stages of evolution. Starting in young H II regions. Observational evidence and a with a dislribution of cme-mantlc cylinders produc preliminary theoretical basis are given for showing ing average wave length dependence of polarisation that the very small panicles that produce the lar and extinction, changes in physical and optica) cha ultraviolet extinction cannot significantly accrete racteristics of the model are studied going first into matter from the gas, even in dense clouds. regions of dense cloud condensation and coming out I. INTRODUCTION The existence of dust in H II regions is now so evolution of a dark cloud. The concept of compact well established that we need not belabour this ques H M regions ii consistent with this concept. However, tion. What is still worth discussing is the degree of one aspect of this which has not, apparently, been correlation of the dust with the gas, and even here it well recognised is that whatever the character of the may be likely that, with some exceptions such as very dust in the dark cloud, it must carry over at least for close to hot stars, the gas and dust are as coupled as some time during the early stages of star formation in H I regions and thjt the gas-to-dust ratio is not too and some of the properties the dust has acquired dur different from the '100:1' value for HI regions. ing the cloud condensation period should project into MOnch & Persson (197l| have shown a high degree the H II stage. Some observational evidence which of correlation of reddening and electron density in points in this direction is that the polarisation of stars Orion, for example, but the value of the dust-to-gas in Orion and in other young regions (Breger. 1974] ratio in H H regions is certainly not yet established. has a maximum indicating 'larger than normal par The key idea in this paper is contained in the fact ticles' just as is the case for the p Ophhichi cloud. thai stars are born in dense H I regions and that there Furthermore, it was noted by Breger that the non- fore an HII icgion is merely the next stage in the random distribution of position angles of the polari sation in Oiktn indicates that the polarisation is Woik supported In pan by NASA Giant NCR indeed due to the interstellar material within the 33-011-043. ThU piper was completed while the authors nebula, rather than to circumstellar material. The were visiting at the Institute of Astronomy, University of wavelength dependence of extinction in Orion has * Cambridge. high value of R= AvlE$_v(paJtkv\»jly $' Ononis). J MAYO t;KttNUI R«; * si I'M; soo now; which again indicates Hie presence ol anomalously Ander* 110731. Jarec diisi grams While a good deal of lltcse remarks must he quali He expect then riut "not mal" prjin characteristics tative ai this time, we shall attempt to justify them should prevail onh outside very dark vloudi as on sotnc quantitative h3sis after first considering in a well as outside H II legions jr.d thai the gums in detailed way the development of ihc sue distribution young (I H regions "»a> appear larger taliiei than of' plains accompanying ihr evolution of dense clouds heme reducet' in y/e relative lo "normal" as a result or leading to 2. THE BASIC GRAIN MO DHL Although many ideas haw pawed through the radiation. Predictability of effects of dust on modi literature concerning the nature of interstellar dust, fying H11 regions is one of our aims. its chemical composition appears now to be coming The classical pan of the extinction and the polari into belter focus. We refer in part to a series of de sation are matched by a distribution of cylindrical tailed papers leading to a justification for the model particles «nth sUicale cores upon which are accreted we shall use here [Gteenberg, 1974; Greenberg & 'processed ice' mantles. We have considered two core Bong, I973a,b|. Our primaty interest wiiî be in sitts: tc= 0.06^m ind ae= Q.QStm, but in this establishing comparison with the wavelength depen piper we restrict ourselves to the smaller. The man dence of extinction and polarisation in lite classical tles are characterised optically as 'dirty ice' for want region, 0 < X"' < 3/im* * and in determining possible of information on the actual indices of refraction of variations of the far uitraviofet extinction A"' the processed materia], which is likely to consist of a > 10|infL, namely hi the region of Lyman continuum heterogeneous mixture of complex molecules and •-.VOLUTION AR Y CHARMTtRISTICS «F- HIMODAL GRAIN MOW L Ifiiîfn radicals. Wurk is m pfngira «it measuring such ^ optical propenies | Green berg. Ycnclia & Lewis. I974|. The inanilûihiekncssciafjjaiP dïstnbuied m SÎM according m " wlwre ihe parameter a; is chosen to provide a good (il t<> the representative cxiincnnn curve, il may he -no— shown {Grccnberg, 3*>f»8| thai a cul-off parameter a, ii approximately equivalent tu an effective mantle The s/did and dashed lines ere normalised ihickncM ot 0.3 a,, it turns out thai the wavelength &m(3l-ù/rttli* } ther/reticai extinction dependence ol extinction in the visible is nul very curves produced by the cure-mantle par sensitive to variations uf as aiound some representa ticles with ac = 0.06 im and various cut tive value appropriate to the core si«. Most uf the off parameters a, as noted in the figure. change takes place in the iRtisied, and consequently The dun siiitw the observations in Ihe value of R = Av/Eg_ v A couple of representa tive curves are shown foi comparison in Figure I where an average extinction is shown 10 be matched laitly well, For a,. = 0.06 f/m, the reasonable choices fur 3j arc in the range 0.14 < a, <0.20 *im. where the latlcr value is used throughout as the best représen tative value. Somewhat higher values of a1 would also he acceptable. We see in Figure 2 thai the wavelength depen dence ot polarisation is such that, for a given core radius. tends to be a good discriminant of particle-size vari mantle particles with ac = 0.06 tan and ation. However, complications to this result may arise various cut-off parameters a; as shown in when we include particles lo produce Ihe far ultra the figure. The dastied curve shows how violet extinction which are non-spherical and aligned. the wavelength dependence of polari This possibility turns out IQ be unacceptable from sation by the ac * Ô.Ô6 um. Sj = 0,20 ton observational results. core mantle particle changes with an in We assume that the genera) interstellar extinction crement of 0.02iimon the mantle. outside of dense clouds and H II regions has the apparently ubiquitous rapid rise in the far ultraviolet as given by OAO-2 (Bless & Savage, 1972) and Hong, 1973a], we let them be silicates of 0.01 ;nn Copernicus (York et al., 1973] data as well as the radius and estimated that we needed about 300 such Smithsonian remits. The question of the 2200 A bare particles for each cote-mantle 'classical particle'. hump is not considered here in detail because it does Our criterion for establishing this relative number not appear to be 3 critical component tn am discus density is that (im(i0)-Ain(5)} / Am(2) at 3. sion at ihis level. wherelAin(t0)-Arn(5xis presumed to be the extinc As is readily evident from the theoretical proper- tion due only to the very small paitkles. We define lies of extinction by small solid particles, we must ûm(iO), etc. as the extinction at X"* = 10Jim',etc. inject quite a few very small particles «Ho Ihe size It turns out that our rough guess of an effective size disiribulion if we are lo achieve the ultraviolet extinc of 0.01 /im foi the very small bare silicate particles tion - relative to visual - depicted for the average ob was not entirely realistic and that a better representa served extinction. tive size is is Uie 0.003 - 0.005 pm range. For the How many such particles we add depends on their latter the relative number becomes about 1500, 1 characteristic size. In an earlier paper fGreenberg & which is roughly gives hyEp.OMQ.QQS) x 300. 156 J. MAYO (;Kt I NH1 K(; * SI UNO SOO HOMJ U.20 = 0.12pm) and fii> a large number (150m of bare silicate (in tins case, olivine) panicles of radius 3^= 0.005 pm. Recall thai ifns is only a ptanhk- choice. Comparison with the observed avenge inter stellar cMinction shows that qualitatively thiscombi- njiinn produces a good til in the 0 - 3.5 pin ' range ./ and in the tat ultraviolet A"1 > bum' (ignoring the detailed structure which is. aftci alt. dependent un the detailed optical properties of the material dm- •>eni. The region between .V1 = -Ipnf'and V^bpnf' Ftgiitv 3. HK Murt'/oip/ft JepiiiJcilcc of rxtinrtii'ii will probably he Tilted in hy any irregularities in the iross-sctlions hy very small particles uiilt surfaces ol the core mantle particle (Gtecnbcrg et al.. raJii 0,0/, (f.OO* anJ O.OfiJ (im nir/i a I''711. There is reason to believe that very small pra- number ratio of1:U>:5(>. respeviiivly. phiie particles could replace in whole or in part the very small silicate grains. One problem here is that In Figure .i we show (he contribution due to tin.* Mie calculation on graphite spheres indicates thai the small particles alone. W«. choose to ignotc ihe detailed extinction ai -HOO0 A by such pa Hides would be no -tiuctutf of that pan of the extinction which de higher than thai at 200 A. Laboratory results by pends on the de.ailed optical properties d ihc matt; flulfman (private communication) tor small graphite rial. Various silicates, foi example, have ultraviolet particles indicate that ihe far (.rv cross section rela abruption edges of such a variability that a perietal- tive to the 200 A cross section may be larger than the îsed material of this nature would tend to smooth calculated unes. We found it difficult, however, (o use over the structure shown in the <>«S X"' <8ym"' these results because of the unnormaliscd form HI region. which they were presented. In any case, the 2200 A bump could be produced by a small admixture ol Let us suppose then that, entering the phase of very small graphite grams, which might then reduce cloud condensation at 1=0 we have a bimodal size the number of bare silicate particles hy about a factor distribution consisting of 3. GRAIN ACCRETION After some time t = r in the dark cloud the grains reduce the ultraviolet photon flux., we would expect have grown to large: sizes. If we were to let ihe core, the bare particle mantle growth in the interior to in mantle and the bare particles gww equally, we would crease very rapidly. This leads to increased shielding, very shortly reach a condition in which the far-ultra- because of the increased ultraviolet to visual extinc violci extinction would even more greatly exceed the tion ratio, and produces a tremendous amplification visual extinction than in normal regions. For exam of ihe normal shielding process. ple, a mantle increase of only 0.002 pm increases the The problem is clearly demonstrated in Figures 4 value of AnH8> by a factor of two relative to the and S. figure 4 shows how ihc extinction cross sec- Schematic ^presentation "t Katelemtfh dependence ••/ extinction çrm\-wiu>n\. by t/irr mantle and bare partuiei at ?»•• différent UOfes of act return. Imftalh at ii.ilfipm, a, - it,20ftr» and a;, •- violet phiKuri ahyirptmns (Gteenhere K llnw, l'>7*a). the extreme reduction in ullfj\:>i)t-i radi ation would lead !<- a rapid increase m ihe base par ticle accretion process, which would then lead i<> j run-away depletion of the inrerstellar condensiMe material cm ihe bare particles at ihe expense «t the core-mantle particles This possibility mj> he checked by eS3iran$ the wavelength dependence of extinction in very dark clouds, and the current evidence in the o Ophiuchi cloud (Carrasco et al.. 1**7*1 mdicakMiwt ilus effect doe', net occur. Further. U iv>th kinds ui panicles accrete at the saine rate, the extra volume >>< condensed material on the core-mantle panicles :s. for .ia much less than am. proportional to a^ -la and thai on the bare particles is. for .ia much less than aj,. proportional to a Aa. Hot a = 0 i-^m. a^, = Vic si'ltd tines are normalised 0 ni 0.005 jim and N = 1500. ihe ratio ot extra volume &mLi}- &mHl= I ihetireticai extinc b on the bare particles to that on the core-maltle ones is tion curves by the combinations of ac *• 0.0ft pm, Oj - 0.20 urn cttK-manttc par ill and approaches the limiting value 1500 a .ia ticle with either 0(/05 or (KOI pm bare increases. Therefore, if the bare panicles should particles at time t = 0. pie number rath» accrete at the same rate as the core-mantle oarticks. of Q.OQ$ and 0.01 urn bare particle to the the bare particles will quickly use up most of the core mantle particle are, respectively, condensable material and leave little material avail llffl and 300. Vie dashed curve is the able fot the cote-mantle panicles. Hence, the core- combined extinction curve produced mantle particles would never become large enough to when the cure mantle and O.ÛÎ pnt bare produce the kind of extinction and polarisation particles arc at lime l ~T corresponding characteristic of larger than normal grains as observed to nantie increments of 0.02pm. Vie in the dark clouds, e.g. ihe p Ophiuchi cloud. crusses fx) and dotted circles {0} are fur One remaining possible mechanism inhibiting the combination nf O.QOJpt» bare and Kctetion on ihe very small particles is induced core mantle particles at I = T/IO and temperature fluctuations produced by molecule for t ~ T/4, respectively. mation. This may be particularly relevant to small graphite particles whose Debye lemperatuie is abom 2000 K. Such particles of 0.005 pm radius would rise to temperatures of T^ = 100 K even if only I eV of cles drastically increases the ultraviolet extinction. energy is imparted Jo them. This would make the cloud completely opaque to If none of ihe above inhibiting mechanisms are ultraviolet radiation, and consequenily very cold. If valid, we ate led to the conclusion that the bare par llje very small panicles are ordinarily inhibited from ticles are really quite distinctly different m their accretion by temperature fluctuations from ultra physical characteristics from normal solid panicles. 15 S I MAYO tlKFt NUI KG & SU NU SOO HUNG The> musi not he able to accicie material in dense Xpiiiax am a 0.;t> leads to the possibility llut the clouds even when the cloud becomes opaque. wavelength ai maximum polarisation may he shifted Whether this result implies that the particles are the at most to about 8000 A. or possibly a little higher. If large free radicals suggested by Plait |lQ>r»J and observations of ihe maximum of mtvntellar polarisa more recently considered by Andricsse & de Vues tion are found ever to be significantly grcatei than [1Q"4J as producing the fat ultraviolet extinction, this value, it may be thai the growth nf giains in remains to be seen. In any case, we bave not been dense clouds should he reinvestigated. able lii answer unamhigiousK the question as to wh> 1'iesuming the acoction of grains m dark clouds the cause ot the far-uliraviolet extinction - if in the to follow the above path, we may anticipate that llie form of ver\ small solid particles - should nut pieath grains m regions of new slat formation will initially modify the foim of the extinction curve as a result of have mantle thickness gicater than twice those of nor mantle acctetion. mal grains. Thus the fact thai the wavelength depen One should not forget that the total accreted dence of both extinction and of polarisation in tin.* material in the gas is perhaps only a factor of live TrapC7Him region jBregei. I'174] indicates substan [Greenberg. W74| greatei tlian that which is already tially larger than noimal grains is not too swpiising in the original mantles corresponding to aj = Q.20(tm. since die additional thickness required is substantially Therefore, the maximum effective gtain mantle radius less than the maximum possible. However, the values may increase from about 0.12ym to only about of Xp |nax == 8000 A given in Carraseo ct al. |197.11 0.21 fim. no nailer how long a time we allow; i.e. a are approaching the limiting value and indicate an total additional mantle growth of only 0.09 jim is almost complete depletion of the available heavy ele permissible with :he paiticulai parameters chosen. Il ments, in agreement with the suggestion in that is not likely that any significant difference should be papet. Thus we have indued evidence that the slatt found between grain models of the same general core- ing point for giains in H 11 regions may indeed mantle type considered here. If the grai:is grow lo appioach the limiting possibilités in si/c. this maximum size, an extrapolation of the relation 4. GRAIN MODIFICATIONS IN HII REGIONS The three mechanisms tending to modify the characteiistic of Oiion. the icduction in Ihe mantle grains in H II regions are evaporation, sputtering and thickness in 10* years should be 0.01 jim. If the grain radiation pressure. Many of these processes are poorly mantles in Orion were already greater than normal understood. Hence ail that can be done is to indicate thickness a( (he time of star formation, we could ex possible directions in which they v/îll act and perhaps pect that even at the present time the grams would to estimate relevant time scales for comparison with still be anomalously large. It should be noted that the the life times and ages of H H regions. In this section mantle sputtering rates relative to those calculated by we shall make little effort to try to improve on exist Barlow may be different if the average molecular ing methods of studying the destructive and radiation weight of the man lie chemical constituent is larger pressure effects. We shall, however, try to show how than that corresponding to ice alone. While the rate oui grain model introduces modifications on these of mass loss is proportional lo the molecular weight, effects as already investigated. Since Orion is the best the threshold eneigy is increased and probably more investigated H II region, and since its estimated age is than compensates for this. Radiation-modified mantle ""10s years we use this as a kind of basic time scale materials may contain a fair proportion of heavy for young H II regions. The maximum times which molecules [Greenberg, 1973). need to be considered aie of the order of several If the very small particles in the original bimodal times 106 yean, which is the life time of an 0 star. distribution have accreted no mantles in the acctetion The effect of sputtering on the mantles of lhe stage of the dark clouds, WL. may explain the relative coie-mantle components of the grains is likely to be lack of far ultraviolet extinction in 6' Ononis, at least insignificant. Barlow {1971] has estimated thai the in pari, by the fact that then the classical grains pro lifetime of a 0.1 jim ice gtain against sputtering is vide larger than average visual and near-ultraviolet ex about 1.0 x I010 «u"1 years, where ny is the hydro tinction as a result of their accretion. It appears from gen number density. Helium is included in this esti the observations beyond X-1 a 6 /inf ' that the cur mate. Thus, even for 0^=10*, which û roughly vature of the extinction is roughly similar for all stars. I VOU.'TIONARY (HARACri RISTK S OI- BIMOI>AL fiRAIN MOHH 159 implying the same particle source ol this range of is ~ 10* years | 5. CONCLUDING REMARKS Evidence has been provided to show that the dust mal evaporation processes may take over. in H 11 regions should be treated as having evolved Such questions as the variation of the dust-to-gas from Ihe dust m dense H I clouds rather than from ratio outward from the exciting star into the outer normal dust. The logical consistency of this is self- reaches of the H II region would seem to be answered evident, based as it is on the concept of star forma best by following the dust evolution continuously tion in regions of condensation. The evolution of a through the dark cloud, to protostar to star turn-on, htmoda] dust model has been followed qualitatively and eventually to HII region development. This is an through ihe accretion stage and it is shown that the ambitious programme, but there seems to be no ob maximum sizes to which grains grow is limited by vious other way of stepping into the problem at any heavy clement abundance to about the maximum size point with the correct initial conditions, except per needed to produce the kind of polarisation observed haps by having detailed observations of the gas and in the o Ophiuchi cloud. The preliminary study of dust at that stage of development. degradation of such grains in the developing and fully As a first iteration to the solution, we have start evolved H II regions indicates thai sputtering is the ed by assuming that there is such a thing as a normal most important mechanism except for the space distribution outside dense clouds and young H II immediately surrounding the exciting star where Uter regions and following it through from there. J. MAYO (if KNBtKf. & St-VKC, S(K> IIOSi; REFERENCES J. Aanneslad. PA. & Purcell. FM.. ,4»-. Rev. <•/ John Wiley and Sons. p. 94, 1973. .4«n»i. d .4sfr,^Ms. 11. 309 ( 197.ll ll.Greenherg.J.M../lr-J. I8a. LKI (1«74l. I! Anders. E.. ttayaisu. R. & Studict. M.H...SWi7t DISCUSSION W. JAFFE: Your pictures of external galaxies in whether the silicate cores arc bom in the solar nebula fact show a correlation between dust and bright stars stage or arc a product of the atmospheres of, say. M or dust and continuum omission. In fact, the H I dis Supergiants. tribution in these galaxirs is quite different from bnghl star/continuurn distribution. Is it not prema STELLA HARRIS: When you say that destruc ture to use these pictures as evjden' e for strong corre tion won't act fast enough (o have much significance lation of gas/dust ratio? over the lifetime of H II regions, arc you suggesting that it is possible for ice mantles io exist in such J. MAYO GREENBERG: I believe that the over regions? lay of the dust drawing by Lynds of the Whirlpool galaxy on the 21 cm continuum is a good indication J. MAYO GREENBERG: Yes. Bui now I musi of gas-dust correlation. amplify this answer by noting first that the ice I pic ture as supplying the dust mantles is not classical dir K.W. MICHEL: In your story about the evolution ty ice but rather a rather complex mixture of mole of dust you have left out the beginning, the dust cules (possibly quite large in part) resulting from formation problem. Is your sDicate core in agreement ultraviolet irradiation of a mixture of O, N, C and H. with condensation tequences proposed by. for This material would both have a lower vapour pres example, Urimer(CosmrKtfiimica Acta. 1969)? sure as well as probably a lower sputtering rate than HzO ice. It is worth noting that ice itself at 100K J. MAYO GREENBERG: 1 am not sure I car. probably would survive for possibly 10**10* year: answer your question directly with respect to the against evaporation. Sputtering effects are com 3 -3 article you mention. Regarding the origin of the sili parable at rt-4 < 10 cm . cate cores we have nol been concerned so much with where they come from but rather with the fact they A.F.M. MOORWOOD: How do you account for must exist. It is not significant in our calculation the 2200 A bump in your bimodal model? f VOf CÏKINARV CMARA(-r(RISTK"S J. MAYlHiKiilNHt-.Kd. I suppose the beU guess ferent fmm what cur model give-i. V partial way 'JUI is Mill a carbon ((trapliilcl material, although the is to asenhe a very hifch alhedo equal to one tor the exact position of the hump produced hy Midi mate bate particles and I am not sure we know how to get rials Joes, run always coincide wilh the observations. this allhou^i some people surest that arapime 'even thougji meiallic i may have su Ji a propertv .VI'. \MHTW0K1U. Y..L1 have noi indicated hnw your tbcoietnal IV i-MniLlion curve breaks M.V PLNSTON I am very uhcctijm • 1 ihce-.i- down IIIIM absorption and scattering ominhutions. Jence tliat K>?. in Orion since the reddenifiK .nn.es Tins disluiclion is important in the context ot dark are sery similar to th.- ol other regions i;, the ilnsi clouds anJ in producing condensai ions, where (J.l- 1.0 pin region. The excess value at H :r,j> he we are primarily interested in (lie penetration cit an altnhuted to mlraieJ excesses in llic ^iars u«;.i t<. external radiation field. Can sou sa> Imw the albedo derive the reddening curves. | am nmdi nmre ir- ol tin- theoretical dun model varies m the IV. picssed by the absence ol ihe .*;;iJUA leaiure u; I)' Ononis J. MAYCKiKhl-.NIIhKU The ultraviolet absorp tion characteristics nl lite core-mantle componenl J. MAYO llRhf NBhRl,. Il appears in.m "in lead, ifi tlie fat I'V. to an albedo -0.5. i.e. an absorp- model thai the range 0.3 - 1.0 pm in the exinuiior. is hoti component equal to about ,iMv. The very «nail nol very greatly modified even when the value o[ R bait particles, it silicate, would prohahh have albedos changes. When the lutal eMinciion ir. the visual rises even less than 0.5 between V = h and Itluin"1. 1 (without changing the shape of the 0..î • I.OM"1 region know llmt Witt and Lil1ie\ dcieriniriaiion of a high drastically ), the apparent si^e of the 2200 \ feature ultrjviolel albedo (beyond X' < 7 /ijn ' ) is quite dif drops, a£ docs the far-ultra violet extinction 1G3 OUST IN H II REGIONS Nino Panagia Laboralurin di Astrufisica Spaziale, Frascati. Italy ABSTRACT The effects of the présence of dust inside l| III emimng dust ii> mostiv mixed with the ionised g LIS has regions have heen studied by means of theoreiical1 heen found. Some jifonii;**™* about the jnnmni. models m' dusty nebulae. Recent infrared nbscrva- distribution and properties of dust grains has also linns have hesn analysed and clear evidence that ihe; heen derived. 1. INTRODUCTION Many H 11 regions are strong infrared sources the numbers of grains responsible for the infrared around X = lOOum and their infrared luminosity may emission'.' How do they compare with dust in the exceed that of the Ly-a line by a large factor (e.g. interstellar space? Bearing these problems in mind, Harper & Low, 1971 ; Hoffmann, Frederick & Emery, the scopes of the present study are: (a) to understand 1972; Houck. Soifcr, Piplier & Harwit, 1971; Emer how she power absorbed by dust and re-emitted in son, Jennings & Mourwood, 1973J. Several questions the infrared depends on the amount, distribution and may arise from such observations: if the absorption properties of dust grains and the characteristics of tht. of Ly-a radiation is not sufficient to account for the exciting star, (b) to analyse some infrared data on infrared emi^icn, what is the source of grain heating? H II regions, compare them with radio data and Is the infrared emitting dust mixed with the ionised derive all the possible information about the infrared gas, or does it form a sort of a cocoon, which sur emitting grains. rounds an H 11 region? What aie the properties of and 2. THEORETICAL MODELS Models of dusty H 11 regions have been computed that the Lyman continuum radiation is comple with the following assumptions: tely absorbed, either by the gas or by the dust: (a) spherical isothermil nebula around an early-type ((e ) the extent of an H I region, which surrounds the star; ionised region, is taken as a free parameter; (b) uniform distribution of the matter; ( 0 ihe power absorbed by the dust is assumed to be (c) where dust is present, the dust-to-gas ratio is a emitted entirely in the infrared, no other source constant; of dust heating but radiation is considered. (d) the H II region is radiation bounded, in the sense The calculations covered a wide range of possibi- 164 N I'ANAtilA. lilies (toi A lull account sec l'jnapa. i""4| We MIIII- injrise IKIV the imwi relevant rrsulis (tl L\-a radiation lias been found not to k- the do- tmnani source of Just healing, unless I IK- «ptk.il depth in itu* ulitaunli>i is null (and the jhsoihed power JISO iv small), (til The non-ionising stellar rjdiatuw lui tied oui to he at least a.* important as the Ivnun continuum radiation to: the heat in t; ol dust. UtiiThe power absorbed by the dust dws not depend strongly on the beiuvmut ol the absorption effi ciency of grains Q(Xi. and the spectral type ot (he rxcttingslar. ti\IA relatively modest ahsurhmg layer m the HI region is sufficient to absorb almost completely the sïellat luminosity. iv| The ratio of the infrared luminosity to the Ly-u luminosity is a sensitive function of both the dust opinai depth and the spectral type of the exciting star. "•'.• can realise these facts by looking at Figure 1. ir widen the ratio UlRl'LtXy-al is plotted as* func tion of 7i (i.e. the average optical depth in the Ly man continuum due to the dusr mixed with (he ion Figure 1 l.(JRllJLy-a) is plotted as a function of ised gas) for the cases of 04. 08 and (W.5 type stars. th.- dust optical depth r, in the Lyman Solid lines correspond to cases in which no absorp continuum range. Cases with 04, OS and tion occurs outside the Jj II region, dashed lines to (J°.^ type stars arc shown. Solid lines de cases in which dust (either inside or surroundinp the note results from models where absorp HII region! entirely absorbs the stellar luminosity tion occurs only inside the H II region. [L(1R) = UstarlJ. We sec that for almost any value of Dashed lines œrrespond to cases in which the optical depth inside an H II region, a high ratio dust absorhs '.he wlu !e stellar luminosity. can be obtained just by selecting a suitable spectral type for the exciting star. Therefore, for any compari son of observation with theory, the actual spec» rJ type of the central star must absolutely be taken into mostly through the factor a. A quantity thai is al account. most independent of the properties of the exciting To understand how to do this, we can write the star, but is still a sensitive function of the dust con ratio HiRI/ULy-a) in the form tent in an H 11 region, will therefore be: lilR) 3 U1R) = ^tot° W~y-a) ~ f, N£hv(Ly-a> *• aULy-a) e, where Htot is the total power absorbed by the dust, The behaviour of 0 as a function of the optical depth in units of the luminosity of the exciting star [HloI = T, is shown in Figure 2 for the cases of 09.5, 06 and UIR)/L(star)j ; a is the ratio of the stellar luminosity 04 type stars. We see that in any case the dependence to the product of the total Lyman continuum photon on the spectral type is indeed weak. Moreover, when flux limes the energy of a Ly-a photon [a - Ustar)/ the dust, in and/or around the H II region, is suffi ML hj tlic material uMially associated with young stars and/ •ti to lite diMance of ihe objects. On statistical grounds we can assume that the stars responsible lor tiie cxcttalinn >)l H II regions arc main-sequence stars. An unambiguous correspondence therefore exists he- twecr. a. (or llic spectra! typei and either the ahsolute luminosity ot the total flux "f Lyman continuum phiMims (>f a siai (Fig. ^). As N>ih are fundi'»)! ihat arc much more scmiiive to spectral type than a is. even a rough estimate of i he m can provide a lairly accurate estimait nf ti. Now ihe infrared luminosity -^ Hives us an estimate ol the stellar luminosity, while from the radio continuum measurements we can de rive the Lyman continuum flou aSorhed by the gas. Uoili are underestimates of the corresponding stellar quantities. However, the calculations indicate that at least one of them must approximate to the true value tu within a factor 2 (Fig. 4) fhcrcfore, fmm the in The behaviour of a ai a function oj ihe frared and radio data we can inter Ihe spectral lype Lyman amnnuum photon flux ,v£ and a with an uncertainty of at mosi one spectral (broken line, lower scale) and the stellar subtype and 2(r '•, respcclively. luminosity (solid line, upper scale/. Vie points corresponding to 04. 1)7 and Iff.5 type stars are indicated. TJu- data hate been taken from Panagia flV7J). Figure 2. Q= L{IRJf(aL{Ly-aj/is plotted as a fimc- Figure 4. The ratios KIR}/L(star) and NiJN^ plot tiou ofT\. Curves corresponding to exci tedagainst T,. The curves correspond to a ting stars of spectral type 04, 06 and 09.5 model computed with a central star of are shown, either for complete absorption spectral type 06, QfXy™X"\ and negligible by dust lL(/R)=L(star}f or for absorp extent of the HI region. tion occurring only inside the fl II region. V PANACl*. 3. ANALYSIS OF OBSERVATIONAL DATA tt'e now want to apply the theory to the case ot There are some sources with an IR luminostty actual sources For this purpose we have chosen the which exceeds that of an 04 type star' in these cases, set ot infrared observations made by the Infrared mow than one exciting star is required. These sources Oroup at University College London |Emersun et al.. are designated as 'multiple' and lut them a has been W"| This comprises a fairly large number ot assumed to he 4 2. Tins value would bi appropriate souiccs. all measured in the same experiment and tor a large assembly of stars all belonging u> the main «nh the same equipment. Furthermore, the angular sequence and are distributed according In the lumin reso.uiion achieved (about!) permuted complex osity function of unevolvcd stars (Salpcter. I'lffi). regions to he resolved into components, so that reli In computing R the LTL tluxcs have been cor able identification ot the radio counterpart was pov rected lor the measured band being finite by assum- sihle tor each infrared *,'urce. Hereafter, we shall iiiR a Mack-body spectrum at 75 K for all ihc sources "refer to these sources a;. TCL sources'. The seventh column represents the minimum op- The relevant data on the ITL souices are shown iical depth ot dust for absorption ot Lyman con in Table I. Only those sources loi which infrared and tinuum photons, which is that computed with the radio data are available and the distance has been assumption L0KIS Ust^t). The eighth column determined have been included. The tlrsi three quotes the maximum T| which corresponds to assum columns quote the UOL numbers. The G numbers ing that absorption is possible only inside an IIII (galactic co-ordinates I of the corresponding radio region. sources and othei possible names, respectively. The An inspection of Table 1 reveals the following fourth and the fifth columns give the spectral type la) The spectral types derived from radio and infia- and a. derived as discussed before; (hesixth column red data arc in good agreement with those deter quotes the computed 6's. The Lyman continuum mined optically, as in the case of M4: (0' Ori C. photon flux has wen computed hy using the expres Ou V. Conti. 147.Ï) and M8 (Herschcl 3h. 07 V; sion given by Rubin (14681 and adopting an electron Woolf. I46I). Tliis means that the assumption of temperature Te= Iff* K. The radio fluxes and the a single exciting star may hold. distance adopted here are the same as those quoted ( hi I:oi all the sources, except NGC 2024. e is signifi bv bmersonetal. |1«73J. cantly greater than I. It follows that in these 11II Ci Number* Oihci Name Sprciial Type 209.0 19.4 M42 06 1.9: OtlS 1.36 :w>.<> 16.4 NGC 2024 095 0.S5 00 Û.8I I.1.V i : W3A 04 3.60 1.64 1 84 713* 0.3 DR 15 04 104 2.90 3.05 fin t.: MB 06.5 1.67 0.66 1.25 s'* 04 OS 2.79 132 1.82 -153.4 04 05 4.36 1.88 2.10 553.2 * o.v NUC63S7 06.5 1.87 0.82 1.35 3S3.1 •> 0.7 NGC 6357 05.5 4.62 1.95 2.15 351.6- 1.3 multiple 2.26 1.05 1.44 351.lit > o.: 04 2.03 0.92 1.2" 348.7 10 RCW 122 multiple 1.90 0.64 1J1 345.4- 0.9 RCW 117 multiple 2.24 1.04 1-42 345.-1 * 1.4 K 402ft 05.5 Table 2 T ITI.N.i 10* * r|R ri;V 10' >-1R' 1 V lO^M.M^ 1 1,1 I II II 'i QiC 2 t I '»l 0 4 ( 4Ki 10 4'^ 4 K» Ï7 «1 0 1" " 0.3'* .1.0 (J 13 4 0 K O V» 10 0 5h 0H7 4 I (l(.ll \(< i 0 1H( (1 4i 10 0.5K 1 "J 1)31 20 Ha ()'»H ! I OH'» OhK lib 0"~ 2 0 0.44 11 12 :?• I..* i.«* o.i* i.i < U23» i.i i 0.211 IO77I I' <>.5 I.I Jt> 0 49 !" < B.4» i I C i.O» 10.17» IX t 4.31 :.0 I 22) (1.5) repmns the dust is well mixed with the ionised quantity, ol the order of unity, which takes the pas. The average fraction of Lyman continuum values 4/3. 1.303. 1 017 fat an infrared absorption taiiiaium absorbed by ihe dusi ts about 2!3.c«rre- coefficient proportional to X*n with n = 0. 1. 2 res spending to (r, > s: 1.3. pectively. Tj is the dust temperature it has been (cl An average relationship between the dust optical estimated oniy for a few sources. ït is likely to range depth and the pas column density can be wnlten between 30 and 100K for sources that are prominent as in a band around 100 pm. A temperature T^j = 70 K. has therefore been assumed for all the sources. Ttv :1 derived, values of r m should then be appropriate for a T, * I 3x 10" neR wavelength \ « 50 jim. They are shown in ihe second where nç and R ate ihc clcciron density and the column of Table 2. In (he computations. ^ = 1.3 has radius of an H il regmn. respectively. The values been adopted. When available, the infrared diameters for individual sources range from one half in have been used: otherwise the radio diameters have twice the mean. been adopted (in these cases the values are enclosed in brackets). We see that in no case does the optical depth . \ceed 0.16. thus confirming the assumpUon Now. in obtain more information about the of the nebulae being optically thin in the infrared. grains, we can estimate (be optica! depth irt the infra For each source we adopt r^ry = fr,^ + rm3Xi!2 red. Assuming a nebula to be spherical, isothermal as a representative value for the dust optical depth and optically thin, the optical depth ai tbe peak of inside an H II region in the Lyman continuum range. the (Remission can be written as The values of ryy is well as the ratios rf^/Tyy for each source are shown in the third and fourth col 4 umns of Table 2. Apparently, two groups of sources TIR= 2.08 xlO -_^_- (3) *Td r* exist, one with rjn/ryv * l(*a a"d ** 0lncr witn T\ftlTUV * IS"1-Whether this fist is real or tsdue to where F Is the total infrared flux in units of 10"'° W the assumption of a unique temperature for all sour m"1. and r is the angular radius in arc minutes, p is a ces ts hard to ascertain. To be conservative, we shall 1GS S l'AVU.U assume lhat the separation into l»n groups lia^ In he the extinction has I'cen found U> be siill inneasinji ascribed cntiirK lo tempeiature dilleictices Jiinmj: wiih the Irequrncv jl U I KM) .\ (York el jl . ilie sources (and possible inaccuracies tn the si/e de I'l^.'J. implying ihe presence ol a sign i lit. an I amount termination as welil. thus a sale aveiagc value i\ r^ ol prams much smallei than 1000 A hoi II II renions riv = HTr As the uiliaviolel absorption eiftcictics Mj'Mg is around lir:. hut Ihe gram size should nut Q{-\- is hM\ to be close !>> wit», ilie iiifured jb- be smaller llian li.n? jum so that dust in M II tegiotis is >orption elllciencx 0[|t turns oui to be about HT" ai expected to have extinction and absorption o>cUi A =s 50jjn> i-uithermore. assumine. 0 t<- Nr piopot cients alnn'st constant slioriwatd ol .\ •= M.KH) -\ Honal to X"" with a unique exponent tiom the t V (o Then grams tn M M regions and those in the miri- the IR.we tound n*. !. stellai space are not jtikc. tn the sense that an excess Sou \tc can use the Krameis-Ktonip telation to ol large plains is icquircd tot the IK emission tnnn set some limit 10 the grain st/c hoi spherical grams. HM legions 11ns ditlerence could be explained b\ wih a relation can be wnttcn as the intervention ol «rvcral processes suclt asjiOiicK rng together ol small grams. Mil growth ol plains h> j^ QlMJX = 4TÎ- ai l-ll accieiion ot pas atoms (in) loimation ot new ji.ains with different properties (perhaps during the proi>> ..here a is the radius ot a grain, and £ is a quanti» Mellat phase i Tlie second and the third possibilities which depends un its optical properties, toi spherical would imply an increase in the abundance ot dust, grains, it is at moil of tJie order of umt> | Pu i cell, while I he fust would icquite only a change m the si/e IQ61), distribution. However, the dusl-to-gas ratio has been derived considering only the dust responsible tot the Assuming the absorption efficiency to he inverse UV absorption and the IR emission, and disregatding ly proportional to the wavelength between 0> and the possible existence of grains that were not capable 100 pm and to vanish elsewhere, the typical radius ol of absorbing any radiation efficiently. It is tlieieloie dust grains should be greater than 0.05 /im. quite possible thai dust in H II regions is oveiabun- Furlhermoie. we can write the laiio of ihe mass dam relative i<> the interstellar medium. ot dust to that of gas (n the form The fact thai dusl in H 11 legions must be diffe rent from that present m ihe general interstellar space MA Ap BTJJV = — <5j can also be inferred with the following arguments: M g 3QuvneRmfl 11 abundances by number of hydrogen and hclium. iabs(X= 1500À|s2.:x Iff NH From this relation we can gel an upper limit to the grain size by requiring that the mass of dust does not N|| being the column density of hydrogen. exceed 3x Iff1 times ll.at of gas (i.e. the cosmic On the other hand, for the case of H II regions we abundance of heavy elements). Adopting p = 2 g/cm. found X - 0.9, Y = 0.2 and Qjjy •* I, an average upper limit 1 turns out to be amax = 0.15 um. while the values for TUV^ I.3X10" ' NH individual sources range from 0.075 to 0.45 pm. Converaely, we can adopt a = ^„àn) = 0.05 *im This is the absorption optical depth of dust at a and get an estimate of the dust-to-gas ratio for each wavelength of about 600 A (Panagia, 1974]. source. The computed values of M^/Mg are shown in Were the dust in the interstellar space the same in the fifth column of Table 2. We see that the majority all respects as that in HII regions, we should say of the nlues lie between 033 x Iff1 and^x 1CT1, the that Q(600A)/Q(1S00A) 3 6, which is hard to 3 average is 1.0 x Iff . It is worth recalling that ne has believe. The simples! explanation is that in the been derived from radio data by assuming the nebulae two cases we are not dealing with the same type to be isothermal spheres at constant density. There of grains, fore, if some clumping is present in these regions, the (b) Studies of Ihe scattered light from H II regions adopted column densities of gas (ncR) are overesti [e.g. O'Dell, Hubbard and Peimbert. 1966] lead mates and the derived ratios Mj/Mg underestimates. to a relation between the scattering optical depth For the interstellar medium a value M^/Mg = Iff1 of dust at X = 4861 A and the column density of has been found iJenJcms & Savage, 1972). Moreover, hydrogen: HIST IN II II RUJIONi Thctefore. fcflless the albedo 11 *il ihe order •>! 0.'* ai tlac ib wavelength, dim ir> H 11 regions must be Ai ihc ; i it if wavelength ific c uniti depiii !.. the interstellar medm % can he wniten ([,3i m inc iirersteHat space. 4 CONCLUSIONS ÎÎK* nui» ;CMIM\ of the present study can He MI-SI iê} The average dust-m-gas mass rat»' JS IT* » in manned a> tiillowi cludes only the dusl responsible tnr either IV absorption or inflated emission. li) Direct illumination of grams by îhe «xcittnp si3r (cl h is possible thai dust m H II regions u over- account* tin mi«i »il (he heating <»l dust assou- ahundant relative to the general miervtellat aied with Mil icgiuns. medium. In) A useful trompai mm ot mhared and ntho lltnes muu include some knowledge ul" the spccdal type The last remark is a warning about direct applica ol the exciting star tion of lhe present analysis to the case <<( complex i m i A simple way to do that a to defined = LilRwfo regions. If a given source is actually composed ot Ustar H a can he inferred quite accurately from several unresolved regions Hot the sake oi simplicity, the infrared and radio measurements themselves. assumed to be identical Mhen. while the derived rtjv will refer to the optical depth within each compo An analysis of m hated data leads in the following nent, îhe column density of Jhe gas. neR. denved cunclusions from radio data, will he appropriate for the whole fa) A significant amount ol dust ts mixed with !he source. An apparent underabtindanee of dust would ionised gas in compact H 11 regions. therefore result. (h) The grainii have a high infrared ahsorption effi A generalisation of the jr-iese-: i:^:h.~ ;^ ..lia* ciency (Q a W1 at X * 50«mî. for such 3 possible configuration and for several other (c) The average grain siie falls in the rang!.- 0.0S • possibilities will constitute the next step in ihis study. 0. i 5 um. 5. ACKNOWLEDGEMENTS The majority of this work has been conducted of the Laboratorio di Radioastronomia CNR. Bolog during a one year tenure as an ESRO-NASA Fellow at na, where this paper has been prepared. This work the Centre foi Radiophysics and Space Research. Cor was partly supported by National Science Foundation nell University. I wish la acknowledge the hospitality Grant GP36426X. REFERENCES i - Conti. P.S., Ap. J. I7Î. 293(1973). 5. Houck, J.R.. Soilei, B.T., Plphei. J.L. A Harwn. 1. Emerson, J.P., Jennings, RE. & Moomood, M.,Ap.J. (Lett.} 169, L3I (1971). AfM.tAp.J, 184,401 (1973). 6. Jenkins, E.B. & Savage, B.T., 1AU Symposium 3. Harper, D.A. & Low, FJ-, Ap, J. Lett. 165, L9 No. 52, 'Interstellar Dust and Related Topics', 0971). 1972. 4. Hoffmann, W.F., Frederick, C-L. & Emery, RJ„ 7. Mathis,J.S.,/tp./. 167.261(1971). Ap. J. {Lea.} Î70, L89(!972). 170 S I'ANMiU S O'Dell. (. R.. Hubbard. W.B. & Peinihctl. M . Ap U Salpeler. b.b.Ap J 121. IM f l"55l J. 143. M.HI •>(*>. 15 Will. A.N & Lillie. I F . Attn>n. * A\tr-phvy 25. •» Panapa.N .Ap J 7S.*»2UI |O?.Î>. •**)?( I-"3). 10 Panagia. N . Ap •>•. in press. I(> Woolf. N.J.. fli/>..4.VP73. :Î0M l*»MV II. l'eirosiau. V.. Silk. J & Field. G.B...-lr>. / tl.ai < P.York. D.C.. Drake. J.F. Jenkins. I-..B.. Morton. 177. Lf>»(l»7:) ».(., Rngerson. J B. & Spitrei. L . Ap. J il.ru ) i: Piiu-*H. FM...4/> / ï5Ji.4.î.i<|Qh*» IK2. I Ul"»73». l.v Ruhin. R.H...4f>. J 154.3^1 il'ifrSI DISCUSSION VP WHITWORTH: In reaching your final con N. PANAGIA: Approximately 91*.. of the life clusion on dust in H (I regions. > nu have made a laipc time of a star is spent on or neat (he main sequence. number of assumptions which may have led to a large Therefore, about one in ten H II regions could be cumulative error. In particular, you assume that Tj excited by giants or supcrgiants. An even luwct per = 70 K in ail cases, and this enters the calculation to a centage is expected arming compact Mil regions, rather high power. Can you comment on the general which possibly have a lifetime shorter than (hat uf an accuracy and specifically on the choice Tj = 70 K ' O star. N. PANAGIA. Generally speaking, the assump J.A. FROGEL: If the dust absorbs a significant tions I have made are such as to give pessimistic esti amount of the direct stellar flux in the UV, the near mates of the dust properties. For the estimate of Tjp IR colour would be quite hot in the vicinity of the a temperature Tjt = 70 K has beer, chosen as a fair stars in the H II regions. For those regions thai have compromise between the dust temperatures deter been observed in the near 1R by the CalTcch and mined for a few H II legions. I would like to point Harvard groups, there are no variations in the colours, out that the temperature enters also in the 'bulo- and. in particular, there are no 'hot spots' meiric' correction to be applied to the broad-band data 140-350pm). Therefore the resulting depen N. PANAGIA: There are some IIII regions for dence of T[R upon Tg is weaker than a fourth power. which the size at 10pm or 5 urn is significantly smal 1 5 say about rig « Tjj" " . This means that a variation of ler than that at 20 pm. Besides, what we need to have 30v in the temperature leads lo a 7JR that differs by no significant variations of the size with the wave a factor of aboul 2. length in a range between say 5 and 20 urn is the tempcratureofthe hottest grains to be aboul 200K (so J.A. FROGEL: In three H U/1R regions where an that the emission peak occurs around 20 pm and at any wavelength shorter than 20pm a "blue tail' emis early type star has been found in the IR. its MDOi and spectral type yield a UV flux which Agrees with what sion corresponds). If the temperature near the edge is you sec in the radio, indicating that the dust in the aboul 70 K, this could easily be achieved by asking H 11 region does not absorb a significant amount of that an H II region be devoid of dust in a>i inner part the L^. within s radius about 1/10 of that of the H II region. Such a hole would be difficult to sec. Further more, if not all the grains are made of the same mate N. PANAGIA: Yuui argument only proves that rial, ihen il is possible to have grains at different optical observations can provide the right parameters temperatures at the same position, and a dependence of the stars. of the emitting region size on the wavelength could be smeared out. J.A. FROGEL: The models of eaily type stars calculated by Mathews show that the LTV output of these stars goes up quite sharply as they evolve off J.A. FROGEL: All of this is not to say that no the ZAMS. Also an H il region will form before the UV pholons gel absorbed by dust. I just feel that star even reaches the ZAMS. This, plus uncertainties only if a really significant amount of Ihe UV is ab in the models,makes me feel that if optical depths of sorbed by the dust, e.g. 90% of the UV, could we tell — ] are derived, this is not different from zero. this from the observations. 1)1'M IS M II KH.IONS N I'ANA<.IA Sin.imiwnr. luminouscxulinp siais aie nul pcissjhle. -A scenic '" me llut it is equally, salid lhal incurred sieiljr nnHick 11 iiAl K'K There i» indueu evidence that ihe may explain llie difference between ihe ii.lal mïrared ultraviolet ahsorption cross section of dust is a strong- luminosity and the measured ionised flux !.>r many PANAt.lA M-nk Is ha mputed a been ohserved m Ihe visual and I he derived iharader- rniiij cither 0 = Liirtsi or y «X1 The differenc ISIICS agree quite well wiih those ihat can be inferrea n the two c sus arc railu r small from (f?fra»ed md raJm Jatafe.g. ti On ( m M4: jn-.f Herschel 36 in M8|. There is tlitrelore no need t.i I- UHKI.IN Suite duet iihscrvat .us ol th deny ihe validity of stellar models. IONISATION STRUCTURE AND TRANSFER OF RADIATION IN DUSTY NEBULAE Valté Peiroiîan' Institute for Plasma Research. Stanford University. California. USA Analytic expressions describing ihe infrared radi- from a dusty ftefruh are presented, frnpii on and hydrogen to helium line intensity ralms these results are discussed briefly. 1. INTRODUCTION The large amount of diffuse far infrared radiation tions, derived simple analytic solutions describing from nebulae (H 11 legions) is hesi understood in these effects, which tn the case of uniform nebulae, terms of emission by dust particles i within and agree approximately with Malhis's numerical results. around the nebulae) which are heated by the central More recently, we have obtained analyitc solutions source uf energy (one or many statsj. The presence of for ihe more general problem by dropping some of dust alters the required number of ionising photons the assumptions of the earlier work. The puipo'* of and the ionisation iiructure. the present communication is to summarise :hese re Matins 119? I ) discussed these effects (by numer sults (Section 2). the details of which will appear else ical integration of the radiative transfer equations) for where. The interpretation of these results and their a uniform nebulae. Petrosian, Silk & Field [1972] comparison with observations are discussed in Sec and Petrosian [1973) with some simplifying assump tion 3. 2. SUMMARY OF RESULTS ON DUSTY NEBULAE Let us consider a spheneaily symmetric nebula fraction x of hydrogen and y of helium are ionised with an ionising agent a! its centre radiating L* ergs up to radii of n and r3, respectively. We assume per second and S" a fT U.f)dif/hP ionising photons rj < r, .Thus, the densities of photons, singly ionised per second, where »e is the frequency of Ihe Lyman helium ions and elections are n(H*>= xn. n(He*) = limit. The densities of hydrogen, helium and dust par yVn and rig = (x+Y>i.tt ticles are denoted by n. Yn, and nj, respectively. A f Alfred P. Steam FoalïdiîioR Feilov ft *e notlcci (he ptcuttHx of doaWv ionised helium. If (he central source radiatcj a «ibitantiaf number of photon* with it >Wii, ihcre VTOBM exai a" inner «sue of daubty ioniW helium. In *\tch a cate, the results here apply to the regions outsldi- Ihis /lint. I'l IKllSIA^ Tlie loinsinj: phoions Horn the icntial source (siellai plmliiusi in: absorbe*) b> Just and h\ tas In addition, tln're ate diffuse photons due to scaticiini: ot slellai pilotons h\ dust panicles and Irom hyJio- pen (eioiisid siJieland helium Tccoiiihiuaiioiis lu oui earlier JI:IKM* ne had neplccted The scaticmic hv JUM and assumed thai ilie recombination photon* aie reabsorbed h> the sas on the spot (this is called the on iiie spot approximation USAI i-urlhermotc. as suming thai each He recombination !•• exciied levels releases approximate!} oie pîiolon capable ol ionis ing h\droçen uhis number \anes %ome»lK-re beiwecii lllp and U ". Robhin>. |o_0l we then have dS(rt_ (H \'anarinti o} .V* t)w mirnbsr of ftn\ins ptk>i,ni>. /', fhs frm Hon .'! miming pho /•'«» absorbed by fan. and the i-jfectivc where a1*' i* the recombination coefficient to e\- ahwTprum optical depth with trueoptical .ned leseis (avumed to be e^ual I'm H am) He), and depth for Just with :tro albedo Solid Kd ' nd^' J" cij(rHiridi'''hi' is the average absorp Itna Jroni the i»>iheipot approximation tion coefficient Joji.il = dust absorption cross- United lints for a généralisai oi)-ili<-ipot section]. The solution of Equation ( 11 can he written approximation. S(r)/S* = e- (l-gUll Not'., if *d = 0. houatinn |^). wilh | icplaccd hy £. r I i = /^e 4Jirnnca' 'dr/S* gives the solution to liquation 111. Variation n| llr, ) with T, is shown by the snlid line in Figure 1 • = /; *dd' In the innei regions of the nebula, where pas opa city is smaller than dust opacity (because the gas is highly ionised >. the assumption of OSA that the dif Here we have assumed that x = 1 fot t < h and x = 0 fuse re combination radiation is absorbed only by the for i > r,. which b. a pood approximation. In general, gas breaks down. We have shown [['ctrosian & Dana, if <*$.v) varies rapidly with frequency. Kjj is a func in preparation) thai we can generalise the OS,*, lo tion of r even for a uniform nebula. This is because include the absorption by dust of the recombination the spectrum of stellar photons is altered, becoming radiation. The dashed line in Figure 1 shows the frac harder toward the edge of the nebula. Nate that tion of ionising photons absorbed by the gas in the E {j, ) = 1 and the number of photons absorbed by gas generalised approximation. This is equivalent lo re placing, in Ihe above equation, «j (and r) hy an effec tive absorption coefficient (and optical depth) whose relation lo the true optical depth is shown in Fig ] ure 1. S'tlr.) - /J' 47ir nncoO>dr (3) The diffuse photons due to scattering by dust par so that the fraction of ionising photons absorbed by ticles cannot be handled so easily. The cflect of scat- the gas is 'ering is to increase the path length travelled by pho tons and the degree of ionisation. The net result of 1 1 nT,) = Ê(r,) = /-' r^ruvlr/j-J r*nne e'dr this is to increase the fraction of photons absorbed by (41 Ve have obtained solutions for dust wilh small 1 albedo OJ « 1 using an iterative procedure and for T. = /J «ddr the limiting case or(l-w|«l, using ihe diffusion For nebulae with uniform distribution of dust and gas approximation. These results are expressed in terms and (assuming a constant KJ) of an effective absorption optical depth in Figure 1, which replaces the true optical depth in the above «!•,>= -^v3'*' /iV-Zr, t2(l-e'r'l3 (5) equations for these more general cases. lOMSAIIU.SSIHI 'Il Kl A. HAlHAIHA IKASSI I K IM.'« Sh M W I \l .kkf 'he ijw «iih n-'.lwM ". , Il Awilflin w.- !lli.l 1"iF--f; Jlr-J jrui S- - Il toi f si: H. r-,- 7- ^ S*.- S" is Utv luting »! p^ni-me %u-lbi pi"'!"»-, jp- jMe <•< i.miMii): tieliurn. jnJ f) %i deiiiu.-.: 1:: l-.j .JII.H- ; l ) l.-r -/••' V (j < £ir, 1 * I and J-'-' I. >.. that cr«- (an.- >*î 3»eSium ti»h\dfft£rn îmr iWerjMrro wr-iJ. i-i proportional M YK Mlle prupnrtin:ul J. iitrutthMi •rpti,m .'l'iuat unisv tr • i, i U: this pftittiuri'. higli aibi'tht valut\ fr„m •/*/• ; fiiMuM appmximaTiKii. l'Jif siL-lljr photons capable ut lonisiruj hydroue» are depleted first Jbttausc r mmnp ilie number "i photom capable ni mniMnp Detailed calculations b; Hummer & Seat on |)'>h.ïj He(r> !*'-„) b>* S. and délirons (lie fnllmvinp jiid others sha\- the existence of small repions with usio >>f jwt.ijie hvili.f^c» lomvitio» enas septum ïiciiitai hydîogers and singly ionised helium. *'c siiall neglect this possibility (i2 > fi I since the presence of liuM will have ihe ïeiîiicncy lu eliminate such recions Djlli'lSUld^'S; / ; ( i^SU'Idi» We now consider the effeci of dust. If K^ ~ «^ . • s.r | { H (which would he the case if oj)p(isa eonsî-nij. then tt can he shown that solution of Epilation (7) is ider- tical to the case without dust, except now tn fcqua- lion |S) J is replaced by £'as defined in Equation III and S* by S*e'r. Thus, for small 7*/Y. H = S11; ) =• 0 find, assuming ihc OSA. >*.'V and for large y*-Y. f j - I. However, the line intensii\ ratios Yf./{(f, ( >>* (note that in this case î(Ei} < 11. For a uniform nebula R. the ;atio of ihe I :: volumes of ihe He to H Strômgren spheres in the j S. 47Ti nciiiaf )(xa •••- t yY) presence of dust, is given {cf. also Petwstan. I'>7.ï; note that the presenl f|r) is the reciprocal of the lunetmn flr)dertned m iheeatlier papetj by when? the three terms un ihc n^M-ham! side describe absorption by d'-st+ = /ri« dr 110) R = %asxl(r1)/ftT,) d hydrogen and helium. lespeciivciy. If K j f K j. neither one of these absorption coeffi cients b independent of r and the above relations t Ita net forth, by absorptioa toefflctea! «v ihaiï become invaltd. However, if etcher 7*/Y « J or mean Ihc eI1ei.livc JIIMJJprion coi'tlHrkn!. av dcn- HJ»KJ. so that helium ionising photons are vntK-il above, and ix rhç «>IUÎIOIλ Kj I.J and a tan IK considered to be approximate^ In mote general cases, ihe dependence ot hoth a constants In this, case, the -.olution of Equations ( 1 ) and a on t makes analytk appi"\miaiiim impossible, and ( "* \ lot a unittMm nebula ejvcs and we must icsott 10 numerical solutions .Î. INTERPRETATION OF 0RSERVA110NS Gaseous nebulae ladiatc a) all wavelengths ran pi tip tiom long radio waves to the Lyman limit The soma- w all tins rjdtation is the u'inia! *.iai(s). In an ionisa lion-huund nebulae all ol the l.yman continuum plm ions tS'l are absorbed by pas and dust. The fracit.in S"tl-£il absorbed b> dust is radiated at infrared wavelengths The fraction absorbed by gast^S't is partly converted to Lyman a (lit) photons, to Balmer and other hydrogen and He lines, and partly goes inio heating of the gas. The energy gained b> the gas is radiated at radio tu neai-infiared wavelengths, via breinsstrahiung and atomic fine structure lines, and ai optica; wavelengths «3 atomic lines (primarily as for. bidden lims). A small fraction of photons below the Lyman continuum may be absorbed by heavier clé ments and. depending on the optical depth of the dust at these frequencies, an unknown fraction by 4 dust. Tlie radio and far-infrared radiation suffer hi tie T(I0 °K) or no attenuation, but depending on the optical properties of dust and its concentration in and out Figure.!. Variation of 7*. fiy*/y' and -y'/fi with side the nebula, the optical radiation below the temperature for a Mack body f solid lines) Lyman continuum may be partially ur fully absorbed and for O stars from the model atmos by dust and re-radiated at infrared wavelengths. (Note phere calculations of Alter & Afihalai. that all of The Ly-a photons are absorbed by the (19701 tdaslied lines), dust). In order (o illustrate the application of the to Lyman a photon energies (fot low-density nebulae, results from Section 2, we consider the following two substituic 30/2 for &). and 7 is the fraction of situations. stellar radiation beyond the Lyman limit. We have (al Optically visible nebulae neglected the difference between the frequency de If the nebulae and the ionising star can be delec pendences of ihc absorption cross-section of dust and ted optically this implies that r '. the effective optical gas. Both ULaJ, the Lyman a luminosity, and depth due to dust in and around the nebula at !ie- 4nD'Sra{j (where D is the distance to the nebula and quencies nO0.is small. As described previously Srad is the continuum radio flux density) arc propor [Peirosian el al., 1972), we can write for the total tional to 7"L*f. so that if we know the distance, the infrared lumino^ty radio and infrared fluxes, and the spectral type {7 *) and the luminosity (L*) of the star, we can calculate L(.ft)fL*=(l-,-)(I e--W ' del cr ni un- whether (ht- neluila j., lomsalion-r-oiind ur 0/7 "=4 and vanes, anions Hilar*, by .t la<.*'.r ;' lei density-bound. I'd cxamplc.it the iormngstar <>l (he than 2. So ll.al without knowledge "I iln ermine Onon nebula is an Oh slai (1 * - I..S x 10"* erg/s. spectrum wc can only esc—aie fir, ) wiilnn j 1 K" • lil«(''l* * ',(K>. > -Odj. then .issurnirp oini|>(<-lc jhMii|ilinn ni lymaii ;onii'uium pholons. we lind typical uehulae U Lu 1/Liï K | - U.l. M> lhat U Oiiji- l = (Ijd. MI [hat the iight-hand une of I ('uytion ( 1 ?.l arc ihe ionising agents. n>, | —0*»jnd ", ' ! becomes la'jter (ban Uic observed ulR)/l* == 0 3K. I- : B tvne or htef type stars, ,3 7 'is r.iudi lam-i even I'm T'=0 Unis one is lorced in conclude thai than uniij I fig. 3). A clusttr ol MILII -.1 ir-. .ire pus- M mit* cl' ihe ionising photons escape the nebulae, sible candidates tor ionisation ol I] II reemns with Mujicbwell. Mr/p, Ji HiicMnieiei \V>74\ »nK,J. Tins also means the fraciion of He ionising photons 7* <'' I. so liai that Ik- loinsin otons are complclcly absorbed in YR « I even if dust absorption cross-seciions lor the nehula. Il i-i. the luminosity of such phoions He and 11 ionising photons are comparable. J-'uriher- Iront an ()d>, i» equal lo the observed injured niprc. unless dusi absorption opacttv j) i> < 1:, D luniinns!*j of Onon. The upshot of ihr. is lhat for the much larger than that at f>t'o, the infrared M/esol Orion nebula rand T, « 1 while «r, » I imply thîsc régions will he considéra his larger ilian iheir ing j very rapid increase in dusl cross-section ai radio si/es. i' — I H -'o This is unlikely considering that the dust From Kquations (II) and (151 to. R«I optical depth al 110 is approximately one [Matins, IV7IJ. Thus, one must consider lhe following possi (i3«f,l. bilities: (i) Y <0.1, di) that the infrared luminosity of Orion has been underestimated. (iii) that the Lyman continuum luminosity of the ionising agent is considerably less than that assumed, or iiv) that the absence of spherical symmetry [Balick. these pro Foi an Oh star 7*7'/fl = 0.f (Fig. 3). so that fut typi ceedings] is the cause of the above discrepancy. cal nebulae f(ar;) = 2 YR. Observations by Church- well et al. Jl--74| indicate a YR varying from 0.05 10 0.1 for most nebulae, exc- -t for the giant thermal sources in the Galactic Centre, where YR < 0.02. lb) tVefoutae not visible optically From Figure 1 we find for YR = 0.05. a-< = 2.5 and for YR =*= 0.02, an =3.7. For Y = 0.1 and tor a uni If the cause of optical obscuration is some inter form nebula wiih TI ~- 1. these imply thai a. the vening cloud, then we are faced with the situation in ratios of dust opacities for He and H ionising pho case (a) without knowledge of optical emiss-'in by the tons, are - 3 and — 6. respectively [see also Mezger. nebula or the ionising star(s). We can no longer deter Smith & Churchwell, 1°74]. As explained in Sec mine both T' and T, . However, if Ihe cause of ifie tion 2, the above simple relationships apply only for total optical extinction is internal nebular dust! or R « I, i.e. they apply to ihe sources in the Galactic dust in the immediate surroundings of Ihe nebula, Centre. The possibility that Y<0.1 cannot be ruled out here. Furthermore, the source of optical obscura il-en it is clear thai I* = mR)+L,3[|m * L(1R). since in general L^o « L(IR)- Thus, we have tion of the Galact'C Centre could be intervening clouds rather than internal dust, in which case we must return to Equations ( 11) and consider the pos f('.) = PL(U)/7'L(IR) (13) sibility that 7* of the ionising agent may be much smaller than unity. For example, if Y = 0.1 and where 0L(La) is the stellar Lyman continuum lumin ij = T|, the high infrared luminosity of the Galactic osity absorbed by the gas in the ionised region. L(La) Centre requires a few hundred stars of type later than can be calculated from the distance and lite observed BO as the ionising agent. radio flux density. As shown in Figure 3. ihe quantity t Absence of detectable optical emission cannot be attri buted ID weak optical emission became nebulae with comparable radio (lux densities most have comparable optical fluxes also. I7?> v ri itiosiAS 4 ACKNOWLEDGEMENTS I would ilk»1 to thank Mi Roger Dana toi help wa> Mir, -.ted hy the National Aeronautic- and Snace wiili some nl lis*.- nuniencal calculations. I fus work Adtmnistiation. miiiei Giant N'GR 05-0^(t5l(). REFERENCES 1 Auer. Ui A Mihalas. l>.. Asu.-phys. J Suppi "". IVtiosian, V, Inteislellai Dust and Keiaied 24. I».î(l'i7:i. Topics. IAI" Symp. No. 5-, I) Retdel Publishing 2 Halick B.. These proceedings. Co..p.-M5. I07.Î. 5 Oiuichwell. h.. Mc/fffi. P.O. & HuchitiKiei. H\. S J'ctiosian. V A Dana. R.. in preparation. Preprint. *>. Petiosian. V.. Silk. J. & I'lchl. G B., Aur^pltys. J 4 Hummer. U.Ci. & Seaum. M.J . Mnntfify Xor. /.fit. 177. (,<.<*(l47:j. fry. Aunm. Svc. 127. 21 ~ i l°M|. 10. Hohhms. R.R.,Aslr,>phrs. J. 150. SI'M W70l 5. Maims. JS...4m#is. / 167. :*>| (I^TIt. o. Mezgei. I'G. Smith. L I. & Oiuichwcll. h.. Pre prim. DISCUSSION K HItt'KLIN: Is it «m J *en ijuesiionjMe js- J. MAVO GRfcKNBERC: I cannot recall yom Mjitiptioii thai the Oiion Nebula is not surrounded io mcniuinitig the effect ul the phase function in your a large eMi-iii hy dust" analysis of the importance of the various appioxi- mations in flic radiation liansfej problem. Wouldn't a V. PI-TROSUS: Tins is true. In addition to ef stiongly forward phase function modify your results fects discussed licie. which apply to a spherically signiiicamly m tenus of the albedo' symmetric csometry. it should he remembered thai nut nun y nebube would actually he spherically V. PHTROSIAN: I Have not considered non iso i symmetric. Foi example. Orion may he density tropic phase functions. A forward concentrated phase bound on the side facing us. hut ionisation bound m function will niaXe the effect of the albedo less the back side where presumably the molecular cloud severe. is located. fcXPECTEl» TAB INFRARED POLARISATION OF H H RECIONS AND THE NUCLEI OF GALAXIES Man in Harwit Centre for Radioph>MCs and Space Research, Cornell L'nhtnify. Ithaca. Ne» York ftc titKtra the i-vpcted juifomïtïun of faf infra- such as timsc associated with Ï1 If reeions jnd p.s- rod 11 m1101. and show Dial the "bscived degree I. WHAT CAN POLARISATION STUDIES TELL L'S? A* this papei is being whiten, a large number of Essentially, this will involve transition probabili independent groups are beginning lo report successful ties of one Lint' or another, whether tot scaturine- irtfraied astronomical polarisation measurements, and absorption or emission »i" radiaNt>n we may expect that at leas! linear polarisation studies will sunn be quite standard throughout thai part of the infrared spectral domain in which wc now arc ih) Mm is the number of niccesuvr times 'tot such J jbJe lo obtain photometric data. pnirea operates, before ihe pltoum ultimately Since wc can expect 10 be dealing with polarisa- reaches our detectors: tion data so soon, we might ..A lo what extent the icstilis we ohiâiir will provide urtaitieigaaes informa This o a gam factor which may be characteristic tion about astronomical sources ol radiation? To of the internal structure of the source, nr possibly of answer that question, we may first wish to enumerate the medium lying along the line of sight to the sour lire known mechanisms for producing infrared polari ce. sed radiation, but we soon notice thai that is not In infrared studies, the gain factor has usually quite enough. We really need to examine iwu rathei been neglected, largely because we haw expected that different types of prubleinv the sources uf emission will ultimately prove to be optically thin. Howevei. lliete are two reasons for worrying about whether that assumption is correct. (al What processes permits preferential treatment of First, we arc now beginning to discover some clouds •me or the other of twti types of :#thogtmally polar of dust and molecules that seem opaque over ex ised photons' tended spectral regions. Second, most of our thinking 1*0 M tl\K*lt hj^ l'i'ïdriit'dii'J .«is , i»rmmn*m t.îJiaimn. 1-MÎ nW * pftï lltjî initial pt>UitS4lit>n \!iuiir> sill! rji*r IH-W Ti'jli!\ M-nc .•! ihe .i'Hinnjiu ph\*icil pt.«ii**M"* mit i|iie^li>"iv while prtHliiciiip lew detinue jii\v.rr\ And iiiiiMsiflbi „li»oii> r»j> mv.'lir napped iiitran-d ICM> • •ILT <-veiiiujl 1111 demanding ni smin,e Mi in Mire will JUILÏ iadijti.>n pinhjhK htitjse either *MI lutih^t. >{*><. rial .4iwrv« hV.-jux.' :he j.tujll\ ..hx-iMv! polaii^iti.-ii «ilill iinii> in (he intuied. iv HI juMlwn. dau jtjibhli- depfiid .'ii S-itï the lutine •>! the ennsMitn pincew JÎ'J ïhc lïain 4'iiljMf wrrhi!) UIV VIIIK we tiu» ci : I'ROClSStS FOR PRODUCING K)LARISAT10N lui' nuin mechanisms KT pioducm,; pulansed •AIK-H dJfJ ilmw that in fini pitï »î the gj. b\ relativist I., particle^ spiral Imp m a magnet u field, U\\ i - 2*>. M» that we should expect ihc spectral and scattering, absorption *>r emission from miei- unies, a loi synchrotron emission In he roughly II X stellai gram-. These pmcesses were discussed m an Willie galactic nonthermal sources i»t tjdn- enmuitti call* pape) h> Stem |Hw| ajtd need onl> be MIOÏ tend itt exhibit >uc\> J >peclul indev. wv should he mansed here caretul 10 avoid unnecessary cxtiapolatiirtis Many evttagalaciic ladio soun.es show spectral indices up w a = '. and ifi some cases cxmpkv nonthermal spectra : 1 SYNCHROTRON RADIATION may Limsist oi a supeiposition of several different specie coftespondtng ît» diftetem ptMtitw* nf a stiHt- Re la mis tic parities accelerated in a magnetic turally cornphcaieJ stiunc. field emit radiation dial is predominantly linearly pnlansed. although a slight degree of elliptical polar, tsation has been detected in vsnous sourcev The ;.:OKAINS theory of synchrotron radiation is well developed. Pacholczyk IllVOj gives a detailed account oi the Tluee different hut iclaied mechanisms are avail subject and a bst of retetences to c.n^.tai work. able to pum fut pn>ducing rxilansed radiauoti. In addition to m high degree of linear polarisa 0) II grains 3rc asymnK-iricallv distnhuietl about tion, the synchrotron process » crufatriensed hy 3 h>me central source, tadiaitop scaiiered by the spectrum thai lias the form grams will he polarised predominantly in a seiw perpendicular to the line joining the source and HrHli- =/ ma*rV.cjn(riJedi' ll) the cloud of grains. While the shape and orienta tion of the grains influence the unserved polari sation, a strung effect can he present even for where nieiisihc number density of*electrons 01 ener spherical E'ains "' 1*'" nonsphcrical hut randomly gy c and ft»*} is the spectrum characterising the radi oriented grain'.. Electron scatiering also can pro ation emitted by electrons with energy c. This spec duce this type of polarisation, trum has a peai at a frequency (tii ï Linearly polarised radiation can also be produced through ahsorption by elongated, systematically oriented grams. This is the process believed to ^e responsible for the polarisation of visible star!, .it in interstellar space. Recently Dyck & Beichman and its lialf-power points lie just below t/^Z and 119741 have also invoked this mechanism Tor ex above 4v . m plaining the polarisation they observe between The maximum frequency is determined both by 35and 12.6(imin theOriofi Nebula, the magnetic field stiength B and by the election (iii)Finally, the emission of radiation by elongated, energy. Most sources of relativistic electrons are ( systematically oriented grains also wtH be polar thought to obey a power-law energy spectrum n{c> Œ ised, since emission of radiation polarised along €'"*, and the observed radiation intensity then has a the lung axis is more probable than emissiun spectral shape polarised with the electric field vectoi perpendi cular to the long axis. I ,\K 1» I'D| AHISAMON (il II II KICKOS4 (.AI A\\ M < H I 1 11 hoi mechanisms lit and Int. ihc observed spei Ihe actual shape >>t inieisteltai grains Irtim will depend i-it the spcttfuin I.! the pdmc Perhaps ihe rmrsr intnfmaiive observation- inwv- souue nt radiation. <,n the si/e i.t ihr Jusi grains .nul in(f mains will ionic inn- medium-tesulutmii spr.ir.i; • »i a representative vcrtiplcx index "I fefrailHrt» Ibis 'ifiserijîionv «me observations or this type sh"ulu J' index nt ri'li-Kduii depends mi tin- Jicmkal ..oiiipn- least exhibit siime "1 the vpe.tra! résonantes ui tl.c \itnm •'! thr grains, lin mecti.imsm tiiil. the gtain (train material Hie wink ni Dyck & Beichman 1^ -i/e. ihcmiiJl ii'iiipiiMti-'H Jin I iiTIipcialiire delei- particularly interesting in thai respect sim-e IT \J,ows nunc tin- expelled spiMnini. ffic degree nl linear horh a strong absorprmn leature ai l'»um and a large pularisalimi in pn-cesses (nl jnd lull depends un the iriLieasc m polarisation at ihis wavelength The |fipm •ivpcLt ratio (shapel of ihc grains and on the degree ot spectral feature has gene rails been associated with systematic alignment of the pi a in s relative m ihc ob silicates. (Juite generally we might expect that inter served direction ot polansjimn stellar dust will consist ot a mixture • i. GAIN I.N POLARISATION ON PASSAGE THROUGH A MEDIUM We can think of a medium which is cither a part S + 4; j'n(i'ja.o)B(c.eK:Nic(hi'd*.dîïde = nl the source nl" observed mlraicd radialmn. or sim- ply a cloud through which the radiation passes before ^-S (A(vjr + hi-| t nd'.fl.oiWi'.fk-] reaching an observer. The medium can affect the ohseived polarisation in many ways, including for S(E + hnhcdvdï>df (4) example depohnsaiion 1 h tough Faraday rotation - an effect that would dominai? only at the loneest wave where A(ci and B(e) are 0;e Einstein coefficients. lengths. However.we will, for the purpose of ihis paper. While these coefficients jie generally associated with restrict ourselves 10 processes in which ihc infrared systems like atoms and molecules, they hold equally radiation e«r be absorbed, spontaneously emitted, or well for grains. For atoms and molecules, the tlrst emitted Ihrougji stimulated emission. Si altering of term on the left of Ihe equation is normally thought radiation will therefore also be excluded, but at long of as some type of pumping term, if excitation or infrared wavelengths scattering by the smalt inter de-excitation of the upper level is significant: other stellar grains is in any case less likely than absorplion wise Equation (4) is quite generally correct, for any 01 émission. system. Let us think of a grain with some characteristic The Einstein coefficien-s are not independent. In cross section for such healing processes as irradiation thermal equilibrium a SOL ce musi emit blackbody by starlight, collisions with gas alums or healing hy radiation, and this can onh . ie (rue if the coefficients cosmic-ray particles. While ihe cross-section for these are related by the equation three sources will differ widely, we can write a term S representing the grain's healing rate due to these m=~ BW (5) sources. Lei us also think of the grain as embedded in an infrared radiation Held whose spectral pholon den sity is n(c)= /n(wJ/,0 Wîî/4rr, where n(f.0*> is the We see that stimulated emission may be important, specific density for radiaiion propagating along the provided two conditions _ ; fulfilled. First, the fre direction (0,0). quency of photons must be low: n{vj),$)?8m>2fc3. If a grain typically spends a fraction of its time In general, stimulated cmiss .in plays j significant role N(e) in an energy state e and a fraction of its time when hf « kT |cf. Huwit, 1974). Second, the N(E + hv) in a higher energy state (e + hi>), ihen the population (or the fraction of ihe lime spent» in the energy balance in the cluud will be given by upper level must be sizable. Tin' MVoiiii t acloi dépeint!, on The importance and (In- chaiacienMics oi the pumping mechanism, ami i> iiol mimcJiaiek apparent honi obscriations In a cloud «.I >II I am tii}: grams ihal J ic tieaied. sa>. b> star light, collision* m 3 vhivk. oi Through cheinh'jJ attachment, incienienial increases m t aie abrupt ami imoh.,- -iK'ipi-v M| ihe oidet of a lew electron »O!|N IVvti'jx". Jie nuie giadiui. in sieps ot OIJLM 111 • e\ . i! i-vmlt-iicd-emisMon i- th-.-.i:w>,-i-c«i*h!:g pioeess 1 hicute I show, lite erwrgj, IIIMHII ••! MIVII a gum I miei then.- conditions. Nle>- Mf * hi), an-1 I'igure I lime ciitlution of the energy content i of when Mei is «nl\ shplitK smaller than Me * liri a mi interstellar grain. Vie grain uataim a'lUin obsened jinouni ol absorption will bear nt< mcasional abrupt increases in encvy simple lelalionship to Ihe total number o! crains m through absorption o) uarLgiit. COMIIIC- the line ot sight. Instead, n will depend on N(f» rav excitation or atom» collisions m Mf • hi». shocks, m this particular example. Vie slower cooling is due to emission of radi- Hie polarisation produced will also depend on anon ai tuns wavelengths, l'or a ivpicul this ditlerence. because the poiarisaiion ot the stimu gram, the total energy r mieht he some lated photon is identical lo that ot the photon induc Ji>1 times prettier tiian the individual ing ihe transition. The (lansitioii piohjbilit> IUrl is excitation steps, and the cooling of the higher lor photons whose elecrnc-lic-ld *ettoi is paral grains u-ouU therefore tend to follow lel lo the mean orientation of the lone aves ol the lines oj approximately constata slope, tor crams. Hence, a photon polarised alone that ditcciion non-exmie grain substances t] mote likeh to induce successive simulated tiansi- tions on its path through the cloud. Lei us now look at two examples to see uhclhei ihe conditions envisaged here are at all possible" If the Orion Nebula lar infrared and subinilli- fa) Tlic Orion Sebula metre source turns ot t lo he somewhat more com pact ihai» our present .evolving power of — f would We can loud at Harper's Jl°7-l| °0//m map ol permit us lo resolve, wc may find that stimulated ihe Orion Nebula. The observed flux is roughly emission dominates spontaneous emission ji far infra 10"* * W cm"2 um~'. and the radiation comes from a red and suhmillimctre wavelengths. solid angle resolved only 10 roughly HT7 si. This (hi Microwave Mater Regions leads to an averaged isotropic number density in the source, my.tf.ol ^5x Iff* cm"3 Hz"1 sf1. while Coldreicl). Keeley & Kwan 1147.*) have pmposco HwVc3 - 8 x iff" cm"3 Hz"'. This means ihal if the thai some 100 pm radiation may be trapped in re observed radiation is uniformly distributed over the gions exhibiting OH or HjO maser action. They envi minimum resolved solid angle, ihe radiation density is sage that this radiation produces a rapid relaxation loo low by a factor of - I0~ to produce a significant •mong degenerate sublcvels of the maser states. In .amount of induced emission. However, if the ob order to be effective in this task, llie relaxation rates served radiation actually comes from one or more must be comparable to the spontaneous infrared tran smaller sources, stimulated emission could play a sig sitions. Kwan [1974] suggests a radiation tempera nificant role. Tlicie also is a further consequence, ture for the 100prn lines of T = 1000 K for HjO involving Equation ( 5), which should still be consider masers. Since kT» he. stimulated emission effects ed. Since \{v) Œii'Bfp). ihe ratio of stimulated to should be taken into consideration. spontaneous emission should increase as the fre One obviously intetcsiing question is under what quency decreases provided that the number density conditions a high degree of stimulated emission also of photons decreases less rapidly than n(vr «f2 at leads to a gain in intensity for a beam passing through low frequencies. Data assembled by fcnekson el al. ihe medium. This depends only on whether the quan [19731 indicate that the observed intensity l . Hem lasec iiiatcuaN m the lahorjlo*-.. and we mi- fi,,,, wutk WJJ v.l».> \.\SAi.-nHj..! M,K n.t tomplciely rule uni llie ei in le me <>l •amibtly tl-dM^PJ* hehavmp puni tiuieiuls in ininttclUf "-pate REFLRENCES 1 Dwfc. J M .1 ïk-Kli/tun. ( A . t.- he published 4 Harper. A . tu ht* .uiMishcd : I tu.ks.-u. t !• . Swill. < I». %'ltehotn. M 5 Haiwit M .\uNiHied !*>l P'-M:. ji.-'f. Mord. Ai AiifUis-»». {,!>.. (ai.,!. 1 J , Kun 6 K»an. i . tu hr published IV. A i.iver. | (>. 4ur,,phvt. J IH3. V ? iVhtifcsvfc. A t. Kadit. Astr-pf VSKS * H ï r. ll'T.l) mm.SïnhJiKiw». 1'»"" .'. (.MldK-kli. I-. KeWcy. f) A & Kwan JV H/r « Stem, w . JW^/IVÏ. J 144. M* i l'H-(.i l'/ni ./ IK2. sS|i"71| I' M Hit. I jr:i p'.ihjhl-. iinsinu-rpretinn «lui Mm are *:nuticd hei.au'* s.iu j-c tjlkim: <•: «am >nn said, ''in there M'tmv In he some ointusKui be i/esot ~ Lan go up or down wi.'.. •'.:•.' aid ol sa> an wftared M HARWIT rîte relationships wliub I drew up photon •re meant to hold after the excitation has iai.cn place and it is nue that you expect some kind (if them»! K.W. M1CHÎ-.L: Bat l&'i Mimulaud equilibrium <" be sc( up within (he grams. An upper iissiim. and lower hut also a whole set of thtm leveW are set up hm upward and downward tcantrttuns ate possible M. HARWIT: Sltmulated emissi.*n iial*4-.%'heie between these levels. You cart absorb a photon to go in thermodynamk- equilibrium- The question is fiom the lower to ihc upper just as you can go from whether the radiation fieH in interstellar space is in tlie upper TO the lower. tense enough to make the stimulated emrssum prob able. Any macroscoptt: body gites stimulated emis P. CLMJO: But are you saying thai after a lime. sion. a-t the grain energ) decays, the distuihincc of the population from thermodynamic equilibrium will V. PfcTROSIAN: I think thcte is some confusion decrease"! here between sttmublcd emission and maser action. M. MARWIT: I would think (hat the emission rate M. HARWIT: The maser action is something for ol pirn ions aruund 100 pm is only — few/sec at most. which, as 1 said, you would need some kind of an odd I would expect thai after a visible photon has been iituaiion bul you can have a small amor» of gain absorbed, ihc equilibrium within the grain would be and you can have del ration from the loiaj apparent set up rather rapidly - even before the first few pho- absorption coefficient. M IURMJ t.l WRKiHl Since the piains arc m thenno M HARWU (hie muii he caieiul to dïMiiipimli d>nanncal equilibrium, one neeJs to multiply tlic relaxation time to a lowri energy slate li mi iclav- ahsmpiiim cross-sec non o,.by ( 1 c"'"'^''10 [»t the aiion lune l'or the reiliititbutiori ol J h so r bed eiu'iRy elfeciive cioss-section l'nless the gram radiation lime within a grain i> slioriei than ihe relaxation time, iheie tan ho no niasinc CALCULATION OF INFRARED SPECTRA FROM OtST IN PLANETARY NEBULAE N Epchl«it'.E-Bi»%«>)r«i",JP ttaiureau* Astronomie Infrarouge. Equipe de Recher che Awoofr au CNRS h lias been diown l>> previous authors, eiihei observer* of iheoietictans. 'hat middle- and tji-mlu- icd esn^s hi'fiî pUnesaiv ncbutjc ts tint m ihrrtnai le-eniiSMoti d1 si d lai uliMVHihrt radiation by dust plains Calculations ut gram tempnatiiic have hee» n*r- lurnieJ hy Krishna Swamy &OIV1I |l'»fcKj Irelerrcd lit hereafter a- KSOt rot NW 7027. anJ lot a taipe number I>| planeuiy nebulae hy Ter/tan & Sanders |Il>?_,| Irclcn ! to as TS) We have repealed Iheii vikablMios jnu attempted m rniprow: ,m their method- Oui method has been applied to chemical vt'sWiiuetm other than graphite. The Meltai l.y cumimium oi the Mai converted inio Lya is the grain licaunn process. The tempera ture of the giains is obtained from the eneigy balance between i:V absorbed and 1R re-emitieti L'niil now. calculations have been made assuming graphite grain* m lire case or planetary nebulae; wc have introduced guphne core-ice mantle, carbonates and silicates. In their works KbO and TS set the prams ai the edge t#f the H 11 region of the nrbuk. in the nettttaj tegum It is now cleat that stwh an as sumption is certainly mil realistic. Indeed, the IU uin map obtained by Becklin. Nengebaucr & Wynn Williams U''73] for NCC 7027 due tn ihe dust emu- Mun ill» very well with the a cm map representing the HMKEU *&*•*( »*C«a*S fice-frce emission. Then, grains and ionised gas ob viously coexist. Absorption efficiency as a function of Nevertheless, an important port of the dust as wavelength for the mw grain models seen on an optical plate is located at the edge of the studied. The velues for the 0.05 tt/x pure r-hula. where optical extinction h a maximum, if is graphite particles arc represented by the itien necessary when computing the infrared radiation continuous line. Tlie graphite~corej * (Jraupe infrarouge Spitai, Observatoire de MCIKJOA, ice-numile (0.0$ jtm graphite core and t-rstsce O.tSpm ice mantle) case is represented ** Itttivtodi I jut». Univenstadi tree*. Italy. by the dashed Une, IMi \ id ntn\ i m y*» i in .1 i r «AI i 11 M of j I'IJJU'IJTV ni't'iilj jiiil jvitup*. al! n-mpli-v 1 lus ci-iuiion is u-diuvit ii' H 11 M I --.-«ion*, t,- lAc ml.- J..V011111 iw.. dusi omi poiu'itl* j f*.*i .'in- iiiMilc ihc umiM-ii ii'piup jini J I " n A - l-ilviil- 1 4nfi" » I « iolc .'in' 111 the iwiin.il it-cii'ii Dm ii-Milt>. »IH-II In (fj «nh i-fu-i-'i.ioltk .•l-.M-f.jt-ori-. ..* ('Liiu-un m-l-ii v.l..-n- f il x.i) is i)it- MHIJI I V.I liny ,l.-.ln,nl I-.-11 la-.' acivc well -Ailli M.K.*II JII j-siittipin-ii ilu- H' ol-senjtiom and nxiLVU-d l-«i tin- miotsu-1l.ii f'.x- ilictiiid! djH'lil'iium t--inp-*i.iltiio Viwooit I'MiiKlixi' vmli udio iHL'nMiii'tiicnt'% 1 ilio j'-wp IA 4C:J IK.J» lv«(im-i» ttoit .iH-llkwiil •>! ciains jt I21i» V i> Sit*!.m's urn vUiil. and 1 j iiii-jii at'si-ipiiMii I'llitH-iM vnollKHiil - ••" I v!X,i.> -4-s- • t>.•)!*>.),.hi •- UOl-.3k.t1l.Hod t>\ ilr-ratio» UW IlllUIIOtl OM IS p\CI\ 1<> JjSSk.ll lotlliuljl- ttliore '• ir. Uw udlu- i't llif puni Mjkt'ii iviiiiil li. ^•...idini: 10 tin.- Mu- tlwoi> |siv Van K\C Hul-t 1 '•* 0J5juni loi fiiaptinc mn* jiid II l>«in tnt lia- in'- ttiLkiainjMnplic. I•«»"•) lh.- i.-inples. n-iij,.mo in mjtiili- iriaphili- ii'uM. ly i« the udutn-n flux ln-in itw Mai. QtM is (he mtiatvd jhsotpnon cltiiii'in in» - h.5 1 0 4" .\ lui i-tjpliKc lOfMkwm. BiX.l^i isilie Pljrwk lunnn-n jt itu* n-m «!,,.(. - l.7ï HUM loi II.OL. pcrjime T . and 1 1 is ihe ullUMnlci .mM-ipiinn c llio jfi-'iiiMmatioii used In KSO jiul [S is noi LlflUl'lKV 1 Jul m I lie- n-Jn-fiamt sidr •>! (In- ln-ai-luLi'iio fqtu- fobk 1. (firifwcj train ftfuiithnum temperature.last' I lopHI^ VPUIJ K'H* cm ; s" Y 's" K 41K 9 0 \G(" 654 3 9.32 14 J 100 6:10 9.K> 8.1 BD+30°3h39 1.41 2.5 MX 324: 9.53 18.6 6720 9.KS 34.4 67H1 10.04 53.0 68Û4 10.13 15.7 6826 '1.89 12.7 6853 9.35 169.0 7293 9.31 3W.0 6818 9.85 9.) Our values KS graphite values * TS graphite values AHOS 'H |K SPI1 IRA IRCIM IH M I lu m lii.l«<) uticri IIJCW valut-. »l <> <*| JIC intn- A^wmmit iliai -ill ihi' I vi ph.a..ii- . Jntftt mil. ilic Itt mii-)ir;il ilm inicpul hcmmcx |>n>- lu itiluiej radiât imi. jnd lliji m. uili. i pnfti"nil tu I c\(ii>îieni «. «(ivre a i\ alw.jsv ercit rt AS CM'-U. we uftlaiiwd jll upper tltlill t. ili.m 4 jbcïi*een * jmj H .U-pnttiin? un ihr M»r* '»! \ m» ^jfutbinMî itj\ iu*tK«.* (K'V« pciioiinrii Î,KI.M tjkttit: ml*» J.^MIIIU the tttmpk-lf iiil.wjti.m ni the IK -Me -I tlic ^ujiii'ii ln,..i!MM !!.<• ,jit\iu ..i «--.cul tirhwlje iM.I ~u:\ N<.( ioi.iWt uhtjinril fte -ire llicn te.: MW Ilil • Ht" î(«*''. I< 41 K) haw IH-CII LJUIIJIOI HlMilc tin- M II Ifilli'li. JS pi'IIHeil i' witli IWM- kjlut-v ut (.'uni Iciujifialuu* < î JJ* -i JW.k!m4ft\),nft,)iu'.i> / i ,/v., r . ={ „$*.—ï-*K-a- f //?\ \\ «GC657Î —f •*—«*!»»-«»- i- - •s-o-i""'" ikt -V- ^ BO 30*3639 Lui\ f'h /' * \\x- , I t •' ' -T7 \ '< / / \ IC4W / / O i LOG* ( MCROM) /•'«KH--1 experimental and computed spectra for //if Ow?-*" morfWs o/ A'GC 7027. NGC6572. BD+Sff* MJ9 and SC 418. Vte tfieoretica! fret free contribution and some radio measurements are also pLuted fur comparison. In tlie near infrared, at 1.75. 2.2 and J.4 um the rabies are due to SWitzcbauer A Carmin [l97of and Winer a al. 119721. Vie measurements in the 7 - 12pm window arc from Woolf J1969} and O'illett et at. f!V72/,fry>m wiwm the 20 tun spectral values are also taken, flic radio measurements are taken from the 'Catalog of Radio Observatums of Planetary Nebulae'(NattamlResearch Council of Canada). SCC AS 72 D=i " XGC7027 D = 4 1C41S D'O BD*.iffy MJ9 D«2 (J) Pure graphite; (2) Graphite-carefice-mgntle; 13) free-free radiation. \ ni tm IN. i m ssuii i M .\ 11' HMI il M Tabic ' < \>mpmifJ train iqinUbriuni taw ? .4. I-IHI-1-H- ,-ai-. v. = ° 0:^ \ —t—-•h-'-rf-l,-- i iff—>-\—' _ J! i_ JUi-i—.— 12 3 4 L06h I MICRON) Expérimentât and computed spectra for the Case-2 model where the dust is considered to be withm the HII region of the nebula. The comments for Figure 2 are also valid in this case. a KGC7027 CO 1C41S CI ••• NGC6572 C"2 BD'XPJoM CJ (I) hire graphite; 12) Gmpbtte-core/ke-mgnrle; (St Pure graphite. Case 1; (41 Free-free radiation. I I rtMU\ (Jl Ik SCH'IJM (K'lM (H SI IN SI HI I -U h> cMmtJlr ihe I MI lîu\ iiwsiiE" the H M tcgimi. p-*»\\ Hiutlr ihe H II !C^i"îi 4titl rhe «•«ill- ..tevi-usK 1 I( .llo win* Olfcll M '!^!, wc tic line a laUor I as the «ibtjined lor ihc M 1 icgion Mill fema n>4iid ratm "I the number nt times that a phulnti l.yu is Very recently we have obtained • rnperaturr', !<• »&'3!fefr<1. irnir* if* mc» lire pain. m the latJiin n! MIKJIC mixrnp in b'ith i.j>e^ JSi :t*f> lietttK.t • \ the nebula R Then ihc ty« llux L\ enhanced by a Kna^eA Thomson. I'»"1] tacim M because of it being îsnttopu I onseijuenlly. the puin tempera I uic within the nebula will lu Uni ... T„ .'uliide the Ijjwiiimi rh^ term and much higher O'Dett has detenmned the \ehuia * I value tor Mime planetary nebulae r>> atsumirif! I ha I ionised ie£i<>n Hllre)U>.n the '* S-itatf »1 the He i iv depopulated by pfioln- CONCLUSIONS REFERENCES I. GIHMI. l.C, Merrill. K.M. & Stem, W.A., Ap J 7. Van de Huhî, HO. Light Scattering by Small Par 172.367(197?). ticles. Chapman and Hall. London (I«57) 2 Knacke, R.F. & Thornton, PASP 85. 343(197?). K. WicJcramasinghe, U.C.. Intersielbr Grains. Chap- 3. Krishna Swamy. K.S. 4 O'DeH. D.R...-Jp./ ISÏ. msn and Haii, London \ 1967). L6MI96H). 9. Willrwr. SP.. Becklin. E.E. & Visvanathan. N.. 4. Neugebauer. G & Garmirc. C... Ap. J. 161. 1.9) Ap. J 175.699(1972). (I'170). 10. Wooll". HJ..AP.J. 1S7. L37(1969). 5. 0'Dell.r.R..^. J. l«. 1094(1965). IK Yada, 8. & Osaki. T.. PAS J 9.82 ( 1957), 6. Terzwn. V. A Sanders, D.. Auron. J. 77. 3S0 (1972). E.E. BECKLIN: It seems io ine Uiai your piopo- th the 2.5" scans of NGC 7027. sal that the 20^m flux in NGC 7027 is ermtied from an axes just outside lite ionised region is incomaîen! N. EPCHTEIN: We ck> not think that the spatial KHI N HMCIIIVI Hl SNOll Ml A IP ll-UI-M Al 1110 k mt .vilaiiih al .\Hlkl 3U.1 il tiiMlu-t il..- U- ri-M'jl tlu> i-MMniiï i>t j i.'.m «nia Jmi IJM-I JI ihe aiii.niiil ni ciaplilU* illMnluitfil in donnai inli-nkliai l'.lti-.-t IIK-I..MI-.-,U.^ ^•.m- imli.jU'h .i vi-i\ sin.tll amniu- -I paplnii' ttlns, ..| i.miM- ma\ iioi apph willnn plaiirian iu-hiil.n-1 MJ |l\Kii'W "MjiiJjid" n iiuiKlox .jiiti-'i •((fil UV.iNI.Jl*, .»t tlK-)ll.»i.Mlt .lllMlllIU I *"ll|J f\w JI icrnivutau^ .ihnu- |iM K .nul ..'ii.iinU i liki- In Mi^Ot llu- jinsMliilil) thai it the i.i- is nul .il .MMK \l«' .. K'ILT.! irnpi.-ii-.l i'tior..;!u-ITU MITI.A iiijifi- v>: U:<) fli . Nrt tathi-i •>! ijlp-t.'iC|>li-\ Di-'li' )l-,.h-.-n A. BJÎI.-V».. I," J i'. r"'"l <»>^ n,> ci ..Int. ,- tnk'x i.it l . N. I) jiui H), lin: \apmit pu-N-un- UIIMV ini Mlk'ati- K-jlun-^ jt 10* "i in jMatiiMjix IH'IMII.I.- MiKl.mli.ilh icJiiifJ m M.iiK-ihiiii: hvm.-.-n uv ..ml \jv n J\ llnv Wnlllil ]M'lllllt J niikh Itillpct lll.-lllli.' jt \ \1VW) (iKIIMllKl. Il H..-K- i- ru- Mlk.ii,- 1 he tt-iniH-i.iiiiii'\ ili'mcil «IJII'IIJI J* H-nl.>» Mitjii'-t^ .m.l il k'o% i'i.i['..ijuL JI Trtfc CiVVTO-iïUST RATIO !N THE ORION NfcBULA M. Perinotlu & P. I'atriarchi Astrophysics! Ohsenalory «f Arcetn.ltaiv ABSTRAIT -\hmit M\IV sptclia h.iu' hecn ohrjinoil usinp an (.".Hi. (.7 Id mten-.iiy line tan-.. Pie resglls _-re mrei- imaye tube with (lie nebulai spectto>:iaph ft lite pieled in tenus ol well-mixed EJ> and dust. r»-r onl> A.stJt*" JJ'cm rt'IU'i.!)», m J position U f- ln>m in ihe leiilral origin regions, bur e*en in lite \>-. area, itonb ol the itape/iumaciossih. siat fM*J?5mto (lie where ilie coefficient of dn-i eximcîioii vi.sini.-d pei ;ra> area of the Ofinn Nchula. Twcntv-live spcct.a I'iu'Tiin is loutid lo he lareet lhaii in ihe bnghi .eiilre haw been -.elected lui accurate meaMlteini-nis nl itic ol ihe nebula. i!ji miensm and of the electron densiu b> lilt (S il| P-ere iv now no doubt that a Mpnilica' ml continuum is mote tnan expected I com atomic pro ntdi.M i-, jxsociaied wiih II II reuiotis Mo\ ..r. apart cesses. In particular, trom study at live spots in the Horn the physical properties of the (yams, she pmb- Onon Nehub. which have been assumed to be re Ictus i.l the location .it ihe dun within the nebula, ol presentative ol the whole nebula, thev concluded that tin* dcaree nl Us mixing Willi the gas. and nt' its con the iws-io-dml ratio decreases with increasing dis centration rcUiivc in the ea-> fus a gm'tî mixing, are. tance itoni the Ttape/ium. the quantity NH.-NJC^.J in our opinion. siiJI unresolved, even lot a well «Y.3 = wartcrmg cross-section tor a single at Nj grains Mtuhed oSicct hliv the Omm Nebula. Horn an optica! pei cubic centimetre) tanging fiom 14J x I0:" ir. the ponil ut'WW. ihc évidente tor dust comes from ihe brighter regions 10 5 x 102" in the outer parts of the teddening ol ilie stats appaienily embedded in Ihe nebula, while ihe conesponding value in the trtiet- H II region. Iront the absence ol stars ol a given mac- slellar medium, according to Wickramasittghe |I"tw|, miittkr HI some areas ul the nebula, from the ff.hjcfl- i> 20 x I0:D. Therefore. 3 gavEo-chm ratio seven ing Milt'oied by line emission, and from studies of ilie limes larger than in ihe general Held has been claimed commuons emission of ihc nehula. The-definite prool for the central pans ol the Orion Nebula. H'jwcver. a ol the existence ol dust m 11 H tenions stems Imm detailed companion made by Munch &. Fersson Ihe wtnk ol Wunn A: Rosmo |t'>5(.|. who have |1'»71| for an area with a diameier of about 6' sjiiwtt tnMH the anticoiieiatum beiwe-en hydrogen- centred in the Trapeîium. between the Fa surface line emission and continuous emission in various brightness and the reddening of the hydrogen Calmer nebulae. Hut the continuum in (he visible spectrum lines, is claimed to dettonstraie. goad mixing of" gai cannot he piedomnunlly an ainmic continuum. This and dust in Ihc Orion Nebula, a fact that points loa ts Hue "i course Nu the smicttites where ihe ann- constant gas-to-dust ratio in the nebula [sec also cotrelalio» has been proved in exist. Pctrosian, P>7„1) and. at the same time, because the reddening is appreciable, to a not very low amount of (TIMI and collaborators p-Dcll & Hubbard. dust in the central areas of the nebula also. Clearly I'WS: OIK-Metaî.. i*î(*[. have found quantitatively, ihe problem of a quantitalive determination of the from measurements of the continuum and of the gas-to-dust ratio from measurements of the contin- hydrogen-line emission, thai the observed nebular lj)£ M PI RINOTTO t P PATRIARCH) uum and hvdtogcn lino emission is complicated t<> We are interested heic in the behaviour of the the knowledge ol the actual position of the exciling central areas close to the Trapezium on the north side slar($l. In fact it we bring an exciting stai neater to and the adjacent casf;n dark bay. Wurm & Herinotlo a pas ant* dust complex, the emission by the pas 11472) have reccnlly discussed the problem of the remains the same (m as tat as tfte ionisation docs rtoi Jmi location in the bay area, presenting a different vary I, while the continuum scattered by dust is evi view to that of Munch & Poisson |I97|) The lasi dent 1> siiongly enhanced. There ate arguments, essen authors place the dust cloud mostly in fionl of the tially ot a k me mat ic nature, lor not putting the Tra emitting layers, while the first authors give arguments pezium stats in the centie of the Nebula jWuim. to support a solution with gas and dust mixed. Wurm Wol and l°to: Zuckcrmau. 197 .ï], and therefore & I'ennotlo. however, were not able lo reconcile the llie use ot other methods for studymp the gas-to-dust observations ol Munch and Pcrsson with llicu solu ratio is highly dcsuable. tion We are dealing in this work with a method that In ihe present work, we have extended the spec makes use of a comparison between the surface troscopic observations made by Wurm & I'cnnotlo brightness in a hydrogen lecombinaiion line and the 11^721 in position V of the Orion Nebula, with sev electron density. For a cfU. The results, show considerable photographic effort across a particular ing the run of the surface brightness in 110 and of the direction in the nebula, first that the situation is not electron density, are presented in Figure 2. The long so simple, and secondly thai this analysis can provide tick denotes the eiongated condensation within the a means of selecting zones with different gas-to-dus* bay area running approximately north-south, one arc ratios. minute east of 6t Ori D. For log F{H0), we had a GAS-TO-DUST RATIO IN ORION NFBULA N Figure 1. fttflN It/ photograph of the Orion Nebula with position '6 'of the slit running W-Efntm north of the Trapezium through the star P1925 into the dark lane, maximum scalier in individual points ot +QJQ ind Toi log Ne of+ 0.15. Despite this scatter, which is not very low, we believe that the mean curves presented aie fairly representative of the average behaviour of •he two quantities. The small-scale fluctuations are, of course, unoothed with OUT spatial resolution, and only the largest-scale features become evident. Fig ure 2 discloses that the Hff flux is proportional to the electron density both in the central bright areas and in the dust lane, bat to different degree*. Things are clearer in Figure 3 (readings in Fig. 2 made every 8" in abscissa), where the upper points (scales top and left) refer to the dust lane, the lower circles (scales bottom and right) to the central bright regions. If we approximate them by straight lines through the ori gin, we have different slopes in the two cases. Some points at the beginning of the bay ate» ac tually fall out of scale in Figure 3. They also belong Figure 2. Spectroscopic measurements of the inten to the upper straight line. We then hive F(Hg) = K Nç sity of H$ and of the electron density in both zones, with a Kç (ce»lre)/Kb (bay) ratio of from the (S11} doublet. The kmg tick about 3. If we consider half of the maximum scatter denotes the north-south conden atkm Ï of our individual observationi to be indicative of the east of'8, OriD. The maximum scatter in errors associated with the mean curvet displayed in individuel velues is shonm. 194 M. PHUNOTTO * F PATRIAHOll Ftgure _. the extreme values oï (his mu* would devi ate by a factor of less than ?. Going back to Equation (21, this means thai Nj ox » Î in both zones and that the extinction coefficient by dust is about three times larger in the du» lane than m the bright region, litis result can help to reconcile the solution for the dun lane pro posed by Wurm & Perinouo with the additional red dening found by Munch & Peisson in the bay area with respect to the central bright zones. Against the solution with the dust lane in front of the emitting layers, we have: (i| ihc linear relation between election density and hydrogen recombina tion line emission just outlined, which can be inter preted only if the dust is mixed with the gas: and ACKNOWLEDGEMENT We would like to thank Prof. L- Rosine. Director of the Asiago Observatory, fa use of the observa REFERENCES 1. Brocklehurst. M., Monthly Notices Roy. Astron. Related Topics. D Reidel Publishing Company, Sx. 153,471 (1971). Oordttcht-Hoaand, 1973, p. 445. 2. Munch, G. & Pereson. SE., Astrophys. / 16S. 9. Wickramasinghe, N.C.. Interstellar Grains, Chap 241(19?!). man & HaD Ltd., London, 1967. 3- O'Dell, C.R & Hubbard, W.B.. Astropftyi. J. 142. 10. Wurro. K..Z. Asrrophys. 52, 149(1961). 591(1965). 11. Wurrn, K..Z. Astrophys. 58.1 ( 1963). 4.0'DeB, C.R., Hubbard. W.B. & Petmbert, M.. 12. Wurm. K. & Pcrinotto, M., Proc. Liege Symp. Asrrophys.J. 143.743(3966). Planetary Nebulae. Mém. Soc Jtoy. liege, V. 6 5- Osterbrock. D.H. & Rather, £., Astrophys. J. (1972). 12». 26(1959). 13. Wurm.fC&Ronno, L., Mitt. Hamb. Stemwarte, 6. Pramben, M. £ Tones-Peanbeit, S-. Sol. Obs. No. Î0,1956. Tomntzaitti y Taeubayg *. 21 ( 1971 ). J4.Wurm, K. * Schuster, RE. Z Astrophys. 61, 7. Perinotto, M.. Astron. A Astwphys. 10, 421 222(1965). 0971). 15.Zuckerman, B, Astrophys. J. 183.863(1973). 8. Petrosian. V-. IAU Symp. 52 Interstellar Dim and 195 DUST AND CAS WITHIN THE ASSOCIATION Cy( OB 2 H Ebûer S. K. Voelckex Max-Flanck-Institut fur Astronomie und Landeattcrawaitc, Heidelberg, Germany On the basis cf UBV data gathered i-y Reddish el consequence, the weak radio emission seems to be the aï. ii966i«id infrared observations by Voeîcîker 4 result of low gas densities, and not of internai dust Ebâsser |i9?3j. a mode! of the spatial distribution of extinction. Our model and the radio observations dust and stars within the highly reddened Cyg OB 2 indicate a gas-locust ratio ol about 10:1, which cor association has been derived. We find a density in- responds to about iO* solar masses for the total gas cteasc of about two order* of magnitude for the dust content. as welt as for the stare less than 10 pc distant from It B obvious that these numbers are liable to con the centre. The resulting total dust mass is about 100 siderable uncertainties. What do they mean if their solar masses, as an average for different models of order of magnitude is correct? If the remaining dif grain composition and sizes. From star counts, the fuse matter were not ejected ;o a considerable extent total stellar content of the association can be esti after star formation, these fijpres indicate that a high mated to be about 10* solar masses. percentage of the original ratter was transformed The radio continuum emission of this association into stars. As an explanation of high dust-to-gas is surprisingly weak, although numerous OB stars are ratios, Wickomasinghe &. Reodish [I968| considered present. Wendker [19701 reporta an extended source the accretion of solid hydrogen mantles onto grains. (G80J + 0.8) with an emission measure EM = According to our model, tr.e temperature of the 10* cm"* pc. As far as we know, no compact H II grains could wefl be more th; i 30 K and this process regions have been observed around individual stars-, therefore seems unlikely. Apart from other hypo which speaks against high gas densities. Since we do theses, we want to point ou* that the anomalously not find any infrared emission from stellar dust shells, high dust-to-gas ratio raigh. .idtcate that new dust it seems unlikely that high extinction occurs near the was formed together with the stars of this association. stars with a considerable reduction of the ionising UV The profosteUar cloud had a mass of the order of 10* flux- Assuming a gas-to-dust ratio of 100:1, and the solar masses, about 17 dus' included. If the same same relative density distribution for the gas as we high fraction of the dust as c f the gas went mo the obtained for the dust, the individual H U regions of stars, about 100 solar masses if dust had to condense the early-type stars overlap. The gas within the asso anew according to the obserr-d quantities. This does ciation should therefore be ionised completely. In not seem to be an unrealistic*, y large amount. Reddish, V.C.. Lawrence, L.C. & Pratt, N.M., wesdker, HJ., Astro». *jid Astropftys., 4, 378 Publ Obs. Edinburgh 5.111 ( 1966). (1970). Voelckcr, K. & Elsasser, H., Proc. IAU Sympo Wickramasinghe, N.C. &i.Reddish, V.C., Nature, sium No. $2 (Eds. J.M. Creenberg and U.C. 218,661(1968). van de Hulst) 529,1973. 196 H f-LSASSm* K. VOt-I.CKFK WSCUSSK)N MJ. HABING You did not mention neiittal t>een made that perhaps the reason for the increase*! matlet. U there none'* lias anybody looked foi dusi-io-ga!. rain» is the fact thai the grains have example, foi CO oi HjCO? accreted material. If cosmic abundance applies, the maximum ratio of accretable materia! mass to hydro 1 H. ELSÀSSER: According to out model, the gen mass is never mare than — Id" , whereat you H 11 répons of the individual caily type stars overlap, derive a dust-t»-gas ratio of 10"'. How can ynu ex therefore we do not expect neutral hydrogen in con plain i(m'* I can sec how you might pick up a factor siderable amounts. 1 am not aware of results on CO of J. If indeed the grains accrete more material the andHîCOinCygOB:. extinction would become abnormal and (his seems lo be inconsistent with vaut 8 value being fairly normal, B, BAUCK: First a remark. A few degrees from the Cyg OB 2 association is found the parti H il H. ELSASSER. The total mass of stats is uncer region Cygnus X which is probably excited by an OB tain due to the uncertainty of the luminosity (mass) association much like Cyg OB 2. Next a question. Is il function for faint slats, but a factor of 10 seems to he possible that the embarrassing gas-to-dust ratio found too high. In addition the stai-io-gis ratio would be in Cyg 08 - is a common feature of other OB star come even mote extreme and improbably high- The associations? hypothesis I proposed as a possibility to explain the high dust-lo-star and dust-to-gas ratios docs not as H. ELSÀSSER: We know too little about other sume accretion by the existing grains, but the conden associations in this respect. sation of new grains during the contraction of the cloud and simultaneously to the formation of the A.P. WHtTWOCTTi: In order to explain [he stars of this association. apparent anomalously high rat» of dim to gas (—1:10). have you considered the possibility that M. HARWIT: The lack of radio emission could be grains are selectively left behind at some stase durii» explained by a transient stage in Kris Davidson's the collapse of the protosiellar cloud? (i.e. when a model. There, a gas- and dusl-free bubble is formed strong radiation pressure gradient exists, but the den during the contraction of stars toward the main se sity is sufficientiy low lo admit a large drift velocity quence, when dust and gas arc driven from the highly for the grains with respect to the gas). luminous stars by radiation pressure. If we are seeing this bubble just after ionisation has set in, and the H. ELSÀSSER: If dust and gas separate during ionised gases are streaming from the surface of the star formation so thai a high» fraction of the gaseous bubble, back toward the centre of the empty bubble, mass goes imn tbe stars, the high dusMo-gas ratio is then the plasma density may still be too low to give easily understood. appreciable free-free emission. After this has gone on for a while, the density could increase to the point where normal amounts of free-free emission are ob J. MAYO GREEN BERG: Is il possible that there served. is a factor of 5 -10 missing in the estimate of star masses? Also, you mentioned that a suggestion had 4. MOLECULAR SOURCES AND STAR FORMATION A NEW INFRARED COMPLEX AND MOLECULAR CLOUD IN ORION I. (iatley'. E.E. Becklin*'. K. Milthews*. C. Neugehauer", M.V. Pension *•• & N. ScoviHc**" I Read by M.V Pen. ton) ABSTRACT A new complex of in I tared sources — i' across larger molecular cloud and thu* cause the strung CO lus been discovered in Orion. Associated with this emission. The complex is not associated with a cluster is an extended — 6' molecular cloud producing known visible or radio continuum feature, and intense CO emission. lis measured infrared luminusit> searches over a 0.7° x 0.7U field show no other com is less than -500 1^ The complex is hypothesised to parable unknown 2.2 urn sources. be composed ol pie-main sequence sources. Several A full text of this paper will appear in Astniphvsi- arguments suggest thai these stars heat dusi in the ral Journal Letters. 191. No. 5. 197-1. DISCUSSION M.V. PENSTON: II I may reverse the normal M.V. PF.NSTOS Yes. bui the kinetic lempera- questjon-and-answer procedure and put a question to tute must be close to the CO brightness temperature, the audience: What is the best way of finding sources since CS observations shnw a much more rapid such as this? Is il by searches at 2 urn. lOjim or change as one moves away from the centre of OMC 2. 100 pm, ui by surveys in CO or the I mm contin uum? R.E. JENNINGS: How much continuum radio emission is found for OMC 2'.' AUDIENCE: No comment. M.V. PENSTON: There is a lirait of 0.25 lu at F.. BUSSOLETTI: The temperature that you tuve. SG1Î7 This can be used to rule out tree-free as the i.e. T^ = SO K. is the brightness temperature of your source nf infrared emission frnm the extended CO source, so the kinetic temperature Tj; must he sources. higher. Tfc is in fact a lower limit for T(.; is this cor rect? * California Institute of Technology. *• Hale Observatories, California Institute of Technology, Carnegie Institution of Washington. *** Royal Greenwich Observatory, Hcntmonccuj, Castle, Hailsham, Sussex, England. **** Owns Va [icy Radio Obfcrvatory, California Institute of Technology. FORMALDEHYDE LINE EMISStON AT 4.8 GHz NEAR NGC 7S38 D. Down» &T.L Wilson Max-Planck Institut fur Radioastronomie. Bonn. Germany ABSTRACT The 111- l,o transition for formaldehyde at region NGC 7538. The source of line < 4.829660 GHz has previously been seen toward astro smaller than I'. and spectral features occur at radial nomical sources only in absorption, except for one velocities of -60.0 and 58.1 km/s. The H-COemis- emission line, from the KJc imann-Low infrared sion ptobably comes from a shell of cool dust and gas nebula in Orion JKulnei * "itaddeus. 1971, Zucker- surroundiflf the ewnrwer iosised regiens. man, Palmer & Rickard. 1974]. We report here a The full text of this paper is published in Asm*- second source of HjCO emission, toward the cluster phyt.J. 191. L77 (1974). of compact radio and infrared nebulae near the H II I. Kutner, M. & Thaddeus. P., Astrophys. J. 168, Zudterman. B.. Palmer. P. & Rickard. U.. Astro- L67(1971). phys. J., in press. E. BECKUN: How do your HjCO velocity pro emission features coincide with those of the files compare with the OH maser source profiles? 1720 MHz OH emission features. D. DOWNES: The radial velocities of the HÎCO tO I-MISSION ASSOCIATLP WITH SJMKPU5S H II KHJONS Jtator IHcMrison. Ja> A f-rnsd&S r.nc fer.v.n (entre for Astrophysics. Harvard Oillcpe Observalnry and SmilriMinian AMrophysical Ohspnatm Cambridge. Mass.. L'SA Oîwurmi'tmxiJe ofiiisMtin 'MS lieeii imiirJ near "" fei:i"N itsell Jli^i resniuti.'P line ;i t'liiht SJiaipk-ss Mil reruns Its ptesctke jppeuts ti. WiieulK js>miiietin,. (he hhie side displav depend .'ii jssoujium *ilii a neai-inlraicd excess .ind aie fvpu.'all> - ^ km s wide (1.5/iiiti Jtum ilie uplKal neluila 11 is Mfnplv fus papei will l \ I'lDlAK What is a tvpi,.jl emission ITK-JMIH: SI rM:KSSU\ H)"* pv l.'f die Slurplc-s suimes um daw nhserved ' 203 CO MAPPING OF 100 pm SOURCES ASSOCIATED WITH DARK CLOUDS PRELIMINARY RESULTS M. Simon Department of Earth and Space Sciences. State University of New York, USA M.N. Simon Department of Biology, Brookhaven National Laboratory, New York. USA ABSTRACT The present evidence indicates that the subniUIi- veys in order to study the temperature, optical depth. rr.z'.ic radiation ù>é\ îuu been detected from gaiactic and excitation conditions in these sources. We have sources is thermal radiation from dust within these begun mapping the sources HFE J, 9. 10. and 11. and sources. Since molecules seem to be associated with FJM 3. We have found CO at or near all th* 100 pm such regions of dust and gas, we have begun a pro sources (with the exception of HFE 10 and 11 ), and gram of CO mapping observations of 100/im sources the sources appeal to be associated with small dark that have been detected in the several airborne sut- clouds. 1. INTRODUCTION ftie several airborne surveys in the 100 fim region J=I to 0 rotational transition of CO (115 GHz'i. The [Hoffmann et al.. 1971; Furnisset al-, 1972; Emerson immediate purpose of this program is to use the CO el a).. 197.1] have revealed the existence of many line, because of its convenience and its belter spatial very strong sources which aie associated with H H resolution than is available in the present 100 Mm regions and dark clouds. HII regions are beginning to observations, to rapidly map selected ( 00 jim sources be fairly well studied by the airborne and ground to prepare for more detailed far infrared observations based far infrared observing groups, and by the mole uf these regions. The 11S GHz line of CO is an ideal cular radio aslronumy observers. These observations probe for the study of dark clouds. This is because indicate thai at least part of I lie far infrared radiation the CO molecule is very abundant throughout the of H II regions originates in the molecular sources galaxy [Penzias el ah, 1971; Schwartz el ah. 1973] associated with them, ft is of obvious interest to (in particular, it has been delected and used to study apply this kind of concerted effort to the study of the physical conditions in dark clouds [Penzias et al, dark clouds. 1972; Tucker et ah, 1973; Encrenaz, I974]),and the 11S GHz transition requires relatively low molecular The present evidence indicates that the far infra hydrogen densities for excitation. red radiation that has been detected from galactic sources is thermal radiation from dust within these The molecular mapping and the far infrared sources. Since molecules seem to be associated with observations yield complementary information. such regions of gas and dust, we have begun a pro Observations of the 115 GHz transition of CO may be gram of molecular mapping the 100 pm sources that used to infer the gas kinetic temperature [Penzias et appear (o be associated with dark clouds, using the al., 1972; Scoville & Solomon, 1974], lower bounds M MMi'N A M "^ MMII\ 204 On :)»(' Illnle.'llla! llvJlOlH'll EJ\ .ll'IIMt\. jlld :itl l'Ml nKeivalioiis al M-VCI.II wavelenpttii. is lo determine maie "' tin' \t*l"k '"• çtadifiiiN wiihm tin- -.ouille On tlio [ OBSERVATIONS ft.- M-lfiti-d t! - llHljiin *om.e. Ill I ;.". HI. Il Ue t .1111.1 fOeniKMon .11 ,.t neai lit 1 .'. •> ami lll.'iinun et al- l*'~U Jtid IJM ï |IIHIHYS i't al . IJ\I l and dismiss mu pii'liniman le-ults m the loi I^:\ J,.f .xii mi M) I O nbseiuliom Inspeeii.-n »! loumi: Motion tt,- i,>iinO no CO OIIH\M.«II 111 .m-.i>. :he l'aionui SU :m.es l'unis im the i«i..ns neai jionnd III! HI and II dm inieteM in thi'M- («,. fill :. " and I J ' î shows [haï tiles appeal in be ohivt* .nose lK\.iiise ot then aiioriialou^ hidi ^il.'K- j«.<.ijte ttjs »M'd loi IIH'M- - Tanle 1. Carb'iii-nuiijtixii/c cniisua» twin I'm 11m sunn c * T?ic Naliorul Radio Astronomy •.JtmTVjtory n apciztcd by Astociaicd UnivLTsiiic:. Int.. undei cwiuacl Willi the National Seiunce (oundjliun. HFE 2 I 4"K V4"K ll I 4°K 1 I JV k ^HM^' hUm%> I •, I I I . •40 0 j !• '//{•• riitiiti \; i RIStUSANIHHSCtSSiON Slfieo I In' SJUpplllj! (Iflli lilCI wllh.ll (llC P-ieseltl Ullh this estltnute o! She distal).*' Ar.jr ;:ijl*c 4 .ifis.-rvafioiis «en- IJU'H is it-L(tvel) (.natM- and lite 1 rude tvimute delected COemivM,m .* 5 pc. we ohtjiti \«(t: > ,- >(«) M,., An »p;>ei h.-und lor the II-JVS ol tl.e Joud may ^e .-stimated :r..m the FJM .1 Hits KKljitii M.ut.v iv m tin- t\pm» u-^oi* vinjl ilu-.iM'iip hy assunjiue tliji the vio.i.i i- «jviu 411J tin- ('(1 tihselSjUolis dioys (I lj! ;i I hat .1 1- JVM. HOÎÎJHV Hound, and lf,jî the omened CO Ime iMdih ..«ted »nli j scijJJ .bid >loud. !(«.• f <1 miifiMK ^ ;efkt;s (fie vef.^itv d(vre-s««i *rthm the .ioHa Ihen stvn in In- vtnjii^vi iti lia- apparently deiisesi rccjotis M >£ >R(^V»1 ' (i. a/id tnth A\ t.iwin aid .ri ihe dtuiil I.» ilicnonhssest nt'1 he minimal JUOpm pmilioti Ihe N'tmdari ni dit' ("(.) vii>n IOtXJpL. 7Ins mieeitairiiy ft lite Iwst lliat tan lic temperatures foil the scale where the exptcleU toi a liiuul at tin* latjsc diManee. Ui* sluli peak brifhliieis temperature in the Orion adopt liie viisfaiKe SW \\.. mohvutar source is W Kb M SIMON A M S SlMu\ ftirtùlfv completed CO map of the //H.1 «K*WI. 7W brightness tempera ture contours ore on /Ar time scale as in Figure Z TV position of S On is indi cated. Where we have insufficient data in draw contour Inch. only the brightness temperatures are indicated Partially completed COmap of the Hb'K v HFE 9 region. The brightness températures are staled as Figure 2. The right ascension »5' <4 and declination are given in offsets from /he nominal 100 um position. RA fl950) ft* J?n4 -5' 9 K) -10' 10 13 1 i ' R — 4 pc as a typical cloud size, we obtain M < 104 HFE 9: Our observations of this source have only MG begun and the map in Figure 4 is even less complete than our other maps. No CO emission to the antenna HFE 2: The nominal lOOfim position of thiscloud is icmperature limit 1.5 K was found at the nominal —1.5° to the northeast of the peak of the molecular 100 um position, but CO emission was found to the and far infrared source in M42. A peak of CO emis south. Inspection of the PSS prints show that this sion occurs at the nominal 100 jun source position, source is associated with a small dark cloud. and the source extends to the southeati (Fig. 3). Star The preliminary results that we have presented counts are difficult in this region because of fogging here establish that the 100 um sources FJM 3, HFE 2, on the PSS prints from the outer répons of the nebu and HFE 9 are associated with small dark clouds that losity of M42. The circumstantial evidence obviously are sources of CO emission. Our observations of suggests that this source is part of die Orion complex. HFE 2 and FJM 3 show CO brightness temperature Taking 500 pc, the distance of H42, at a representa enhancements at positions that are within the prob tive for this region, the apparent diameter of the CO able errors of the peak positions of the 100 pm cloud associated with HFE 2 is ~ 3 pc. In the same sources. The present results suggest therefore that the manner as for FJH 3, the mass of the cloud it esti gas kinetic temperature (and probably the dust tem mated to be in the range 2x 103 M© 4. ACKNOWLEDGEMENTS I) a J pfcjiore (M «.knowledge Oie thorough Tucson. We (hank i) Peu--sun. G Righini. and au-isiancc dtinnp (lie ohscrvaiums ol S . Alhauyji. ¥ Solumor* for helpful discussions. I) K REFERENCES i.Bok. B.J & McCarthy. C.C ApJ.79.42 (1974» 1 Pen/us. A A.. Jeffem. KB &. Wilmn, R W . Ap J 1*4. BJ & Oxdwell. C.S. Molecules m the J 165. ;^)(1971» {•atactic Environment. Ifcds. M.A Guidiw and H Pen/ias. A.A.. Soiormm. P.M. JeltVris. KB. & LI- Snyder} John Wiley and Sons. Inc.. New Wilson. R.W.. Ap. J (Lett.). 174. L43 I I972i V.Mk. J'I?.V 9 Schwaru. PR- Wilson. *J. & Epstein. E.E...-1p. 3 r.mersnn. J.P. Jennings. RE & MIHUWIKHJ. / 186.5,^11973). AfH.Ap / IH4.40I {!'>'','» 10 Scimîle N.2. & Solomon. P.M.. Ap. J. (Lett). 4. hncrena/. P.. io be published. I87,L67(I°74). 5. I-'urmss. I.. Jennings, R.E. 4 Monrwnod. A.FM. II. Tucker. KD.. Koinei, M.L4 Thaddeus.P..ibid Ap. J- il.ru. 1.176. LI05 ( |972>. 186. LI 3 (1973». (Y llnffmann, W.F. Frederick. C.L & Emery. 8.J.. 12 Uhcfi. B.i- 4 Confclin. E.E.. Nature 248, I2i ApJ 'Lett. 1.170. LB*»(1*)7I). (19741. DISCUSSION EDITOR The discussion following this paper is not repro both ihe infrared and CO peaks were displaced rela duced here in full as il centred not on (he conienl of tive to ihe radio. The essential point of the discussion rhi' paper itself, hul on a slide which Dr. Simon intro was thai if indeed these peaks are physically separa duced at the end of his talk. This showed an overlay ted then this was a highly significant result. Following of CO, far infrared and radio continuum maps of the comments of several people on the relative positi NGC 6334. The point which Dr. Simon was making onal accuracy of these maps however it was clear that was (hat the peaks of CO emission came closer to ihe great caution should be exercised before coming to far infrared peaks than 10 the radio peaks and that such a conclusion. STAR FORMATION AND CONTRACTION/FRAGMENTATION PROBLEMS A.P. Whitwwrth* Deianmcnl »l Applied Mathematics and Astronomy. University Cutlege Cardiff. Hate. ABSTRACT Wc propose a geneial Irarnework (or theories of sufficiently early and last thai tiiev avoid inelaatii. star furniaiiun. The processes that determine the collisions, and thus remain dispersed b> the subse mass-spec irum said spatwl configuration of stars quent approximate cquipanitmri ft their mutual *ra- formed in association arc discussed, the processes nutional and randomised hulk kinetic energies' h is being evaluated in terms of the enetgy imbalance shown that when a prospective sur-cloud hemmei which drives [Item and the compelitivity of their unstable against contraction, it a]reads exists as a time-scales. We outline a (rend in itic contraction/ well-defined. gravnationilly bound nodule (i.e. rhere fragmentation sequence (CFS) which may be impor is already substantial density contrast between the tant in terminating fragmentation, and hence in deter miduie and the background density defined by the mining the masses of protustellar clouds this trend parent-cloud). Consequently, condensation may pro derives from the interaction between magnetic and ceed efficiently until centrifugal forces become im centrifugal forces. In particular, wc address ourselves portant. We consider the implications of this result to the condensation lime-scale problem; can sub- for star formation and stellar dynamics. clouds condense oui of i contracting parenl-cloud I. INTRODUCTION Stars ace formed when diffuse interstellar matter ils interaction with the surroundings, until Use star condenses to such high densities that it generates becomes visible as a non-accreiing, unobscured ZAM5 internally, and traps, suffieiem energy to support it star. These phases are not well defined, but concur self against self-gravitation. In studying contemporary rent and interdependent. We should also note the pos star formation, it is meaningful to enumerate four sibilities of isolated star formation and second gene phases: A. the constituting of a massive protocluster ration star formation. Nevertheless, the general se cloud Irom interstellar matter, and the initiation of quence is probably actepiabk, and provides a con its conttaciion (where protocluster implies thai from venient framework within which 10 develop a theore this material a plurality of stars is formed in one tical picture. event); B. the contraction and fragmentation of 3 Star formation is evidently a fundamental astro proioduster cloud to produce protostellar clouds; C. nomical event. However, it is stilt only vaguely under the contraction of a suitably disposed ptotostcUai stood. The elegant review of star formation problems cloud lo form a star; 0. the evolution of the star, and by Mcstel ( ( 96S | concentrated on phase B. and asses sed the processes which might initiate, control and terminate the contraction/fragmentation sequence • Until October 1974. SRC/NATO Powdoctonl Fcllo* at (CFS). Advances m observational techniques jnd lbs StcneweH Leiden, The NetheiUftds. 210 M' PMICMUI. ji1i.ul.it lite ,;i.-will . CONTRACTION A cloud "t nue siellai matin is unviable againsi ii'iliiiTion ot the internal /'jfrmd/pressure, hs sudden ntra-Uou Jue t.- jn encrgs. mirulaïke uith the •.••.'lull; and or ri-i.o intimai ion lliis might occur tnl proximate tunn lowing j I'V Hash, oi by opacity exclusion ot heal ingioniMiig agents, willi consequent molecule loi- * r • i\. mation. jL'ctetion ol gas particles on grains, and enhanced cooling h> molecules and grains We include e^. is the seli-gratitaiinnal energy dcnsit\ under thermal instability all iHhei processes which : l^"t;M IOZR*. toi j spherical cJoudt p^, and reduce P[nt (eg damping of turbulence, disposal ot magnetic flu*, and loss of angular momentum, sec P(nl arc effective pressures loi the medium outside and inside the cloud they ate compounded by ther below. mal, turbulent, radiant, magnent, ccmntulgal (l\m It is currently believed by an appaient majority of onlu and 'ram' (pvy\ only) contributions The a&tionomers that most contemporary (populalinn I) dimensions of inequality 111 arc energy density, and star formation in spiral galaxies is initiated by corn- purely numerical lactors have been suppicssed. pressional instability, when inierstellai gas clouds run Cnntractton is initiated by a suitable change in into a galactic shock associated with the spiral pat any one of the three terms in 111, depending on the tern. Available infotmaium on interstellar conditions magnitude of the other two terms. We therefore dis m nut own Galaxy suggest that collapse is inevitable tinguish three types of instability, although these ate for clouds wuh masses M > |0*MQ. It has been pro run completely separable. posed |Sliu et al.. 1**7^| thai shocks exist which are sufficiently strong lu initiate coniraclinn in much smaller clouds. M > 100 M la i Craviiauimal Instability 0 We note that the other mechanisms lor niHiatm}.' The evolution of a statistical ensemble of inter contraciiun (as outlined above) are not excluded by pellai gas structures (including phase-transitions, this picture Firstly, star formation is not rigorously cloud/ciuud collisiuns. and space/time mhomoge- confined to the spiral aims: in oidei to initiate con ncities in the densities of radiation, cosmic rays and traction, and hence star formation, in ihe contempo magnetic flux) may result in aggregations which ate rary interarm gas (or in the pre-spiral nebula, or in sufficiently massive that e„ dominates inequality < 11. elliptical galaxies), we can reasonably invoke both and contraction ensues. thermal and gravitational instabilities. Secondly, the other mechanisms play auxiliary roles in determining ( b) Compmaonat Instability what range or potential profoclusicr clouds exists in the interstellar gas as it impinges on the spiral shock, Contraction can also be induced by increasing and how these clouds respond tu the shock. Thirdly, many of the mechanisms play fundamental roles in pexl, as for example by passage through a galactic shock, by magnetic tunneling, or by sudden ionisa the subsequent phases (B and C). tion of the surroundings. Once inequality (!) is induced, the cloud con tracts until the imbalance is redressed, e^, increases 4 fcl Tliermal Instability rapidly as K" . pexI is probably approximately con* slant, may even decrease, and will be ignored. Thus contraction proceeds until sufficient Pm( is deve Finally, airy reduction in Pmt causes contraction. The true thermal instability involves specifically a loped. Ultimately this must happen at stellar densi- M W MlKMANON A (ON|RA tirs. WIK-I; miileai «MLIKIIII Lvueraie (dermal, ruil'u- ncte demit) is lugii and 'I < rnagncii,. 'idd 11 »eli lent ami radiai" rneii!) Il van happen e-rln'i ni um ••rile ••!. majtneiu l1u\iscMe UseU Irwcn in the ^.i • me. "r ,Miiil)injiii'!i. ot llic lollnwlii); wass (a| the tl.. iiujifietK pn-SMiic increases a% R4 anil 'du- Mm cloud l'écornes "p.iqiic, [he thermal energy i'l com- ply dilutes sclfgravK) It the iharged-parnje demuv prckUtitt arid ihv jiMi^ijtriJ radiant energy ait." is loss. magiKliL fhm is l-»st hy dit fusion ,1 •!.; :;-i,: ;s tiapped 1 lien .isMuijinl pif>Mirf irurc.ises laMer than m.issly disiofted. llur is dissipated resisir.els in ci- K '. I '• I niihnlei-' .ncig) is generated tastei thaï- n is Hier i.w magnetic presume increases mure >iu*h dissipated, the i•imulfrit pn-ssiire increases lasli'i [l'an Mian ti*. id) the magnetic Held mas jlso e\ei; K'- K> angulai Tru'iruTiUim is conserved minutely. (orques wl.nJi redistribute fur even remnvel anauiar llic «.emnlugal pressmc increases \ts K ' and musi nu unen Hi m. so that in part ol the cloud (possibly in eventual!) dominate inequality I I I all •>) il) llic centrifugal pressure increases more -.Inw- ('Miivvrv.V *e nmsidei pimesses wlikli luilhei ly than H~\ (el finally, contraction is furthered itn.re.isr L 3. FRAGMENTATION puring the early stages of the contraction of a (cl How aie the fragmentation and overall gravitation protoclustci cloud, we expect that inequality 111 al energy of ihe protircluster cloud preserved' (This is grows rapidly, due to the ascendency of the sclf-giavt- the condensation time-scale problem considered in tation term es„. When 111 is large, we speak of col Section 4\ lapse. However. if ( 1 ) is large, the cloud is unstable The CVS rapidly amplifies magnetic and centri against fragmentation: for ( I ! is now also satisfied - fugal pressures until they become comparable with albeit less strongly • by smaller masses. This i- more c„. For the case of magnetic pressure, we substitute 1 evident if we substitute foi a spherical cloud. e„ = in ( 1 ) as before, except Pmt *- H <8rr: 3 3 1 9CM /:0PR* = (3C/5) Mn/AU /;») "; p,.xt ~ 0; ano = din! flk'iVm where p.T.m .ire the mass-density, (Gi5H3nM!Vfl)2- gas kinetic temperature, and mean gas-particle mass. (3) We have assumed here that P derives only from I , 3 mt (l2IrG/SH )(4ffMV/3^ >1 thermal energy. Inequality ( 1} then becomes. The cloud is assumed to conserve its magnetic flux |4W.l)pMI(4Gm/l5kT(J > 1 12) F^ minutely by flux freezing [Mestel & Spitzer. I956J. Once inequality (3) is small, the cloud can As the cloud contracts, p increases. We also expect contract - since (3) is pure extrinsic - but it cannot (m/T) to increase due to cooling and recombination fragment. For the case of centrifugal pressure, Pjnt "- (211- H1, etc. hand so (2) is satisfied by progressively JMUVSJTR, and smaller masses. We envisaged hierarchical sequence, in which cluuds contract and fragment to form sub- (8irGp/SJl3)~ clouds, which themselves contract and fragment, until the original protocluster cloud is broken down into (12G/12SLJ(> <6M,0/ffp)"s > 1 (4) dense protostcllar clouds (Hoylc, 1953|. Three fun damental problems remain: (a) How is the CFS able to proceed as far as protostcllar clouds with typical The cloud is here assumed to conserve its angular stellar masses, when the original protocluster cloud momentum Ljf minutely. Once (4) becomes small, contains realistic measures of magnetic flux and angu the cloud can fragment- since (4) is pure intrinsic-, lar momentum? (b) How is the CFS then terminated? but it cannot contract. Al> WIUfAURlH Variable estimates ol II and £1 tot ihe inieMellai tening is opposed bv thermal pressure gradients, iin-Jinn show, tlui both ( 4 IHi: CONDENSATION TtMfc-SC AU. PROBtEM h sccitr. encr gel Kail», tcaiihle tm j itsjiM^e piolu- the tffjvifatioful f-tetituli is upuiH jnpiifio: .• ciuslet cloud in Irjjiiiifiii mi.- %ti, lessiseh smaller ihal the survti..ud\ JM« rhr"Ufcl< -tie tcntr- 4t .:."••: vhiUiU. Jiid niiiiiufclv i>> Jin m pMtiiMcifor clouds rent iimei jnd or miss the ceniR- altogether II vermi which aie iuiul>l> d!ip"wi t" l.xni *tj(^ H.'*f.i'f. fugal prewure n unp-fUjnf live ^VKII: ivviuemth Iragt»ettlatt<>u will mils be pettiuneii! ii ji cat h \(age ii.^-.mitlt.'m. jnd these flk.h ait cvn «dît-* i: «•t the OS Mi'-J>iuth i.iiMknv nui taris ami ÎJ>I nia^rtu t/icswre ù impottam. «.oihssoti* J;< su;tt.e* enough to compete willi the ovcial! I < m I taction <•! impejcd. «me cai.li subcloud must, tn principle llic pjiL'tii LIIIUII. winch lends in rejsv.-mhle the suh- assemble u% mass In un a sepjiatc tlux-tuhe ciuuds It i omjcnvalion is inefficient m ((:<.- setrx: thai it i- Condensation is efficient if. jiier the onset ut sJt»w. the suHch-uds may loose jl! their kinetk energs instability, the density m the luhumid rtsei mucli in mtiaslii •...itisi-.tn. and [he parent J-.ud i-, tl.ci. faslct than ihe hdckgiound density 4s defined by the simply reassembled in a denser, mote Nir^ngly h'>unc i mm actum til the parent cloud. The ctos^secuon of state than helofe jltctnativeK onl> pan »f the kitie- the suhcloud » then much smaller 'ban thai of the tiv energs is UA| and ffagmetitai>>>n i\ prewncO. **,ii. parem cloud- Consequently, when 'he overall con- the subcUnids relaxing l« a Ughtt> hiiirid vonl'igur- traction nt trie parent-cloud brings the subclinics into aijun M condensât)tin is last, but mefdcierti m she close proximiiy in some centtal pnint lor planet at j sense that u occurs Ute in the overall contraction •>! later epneh. they avoid inelastic collisions and thus the pareni cloud, then ^raviutmnal energs is lo»t r.. preserve their bulk kinetic energy. Elastic collisions cnmpiesSiKTt of the parent cloud and again Ihe resui randomise the rr-iividuai momenta, and the sssicm of unt subcluud configuration is tightly' bound. subclouds relaxes (by équipaiution of gravitational If centnfugal pressure is important, these results and kinetic energy I to an open spatial configuration are modified, since some gravitatiunal energy is m- whose extent ts close to thai i>* the patent cloud at evifablv presersed m approximate equipartition »uh the onset of instability. F.ven if centrifugai forces are tlie centrifugal energy. If condensation is very mesïi irnpoitani. lite amftgufatKin is only mildly asprWn cient, the subcluuds reassemble to Ntrm a highly fljt cal. tened gaseitus disc. If condensation is mildly ineffi We might expect that in the absence of magnetic cient, fragmentation is preserved, and the suhclouds and centrifugal pressures, the sunclouds inevitably adopt a moderately flattened configuration The collide al the centre of the patent cloud, tin mattci ewnul point is that the amplification otcentriiugal how small ibey ate. However, any nonur^'ormiiy in pressure is not in itself sufficient to prtWuce highly the system (e.g. asphericity in ihe parent cloud, or tlattcned systems, it is also neccessary to dissipate dispersion in ihc radial distances at which the indivi gravitational energy. Vie retuin to ih» point bier m dual suhclouds form and consequent anisotropy of connection with galaxy formation 5. THE FRAGMENTATION MODEL We investigate the stability against cotmaction of K(M. detives from an admixture of grains, and radi- a pmspecMM subcloud. as it responds to the incieas jtiun escapes freely from the boundary of the sub trig density m the contracting parent cloud of which cluud. Tlie mbcloud is subjected to a uniform exter u is part. The subcloud has mass M. and is con nal thermal pressure p£. which ideally is supplied by strained lo remain homogeneous and spherical with an infinitely hot. inJinitely rarefied gas. In reality. ptf radius R. Tlie gas kinetic temperature T. and the is supplied hy the remainder of ilic parent-doud gas. mean gas-particle mass m. arc constant: the subcloud wfnen ts assumed to hare the same (Jjn) as the sub- has internai thermal pressure ?t. The turbulent energy doud gas. Thus Ctpe) = P^'pç is a measure of the E-fn. magnetic flux F^. and angular momentum L/. density contrast between the subcloud and its back are all three unii'otra and minutely conserved (i.e. ground as defined by tin parent cloud. The subcloud there is no dissipation or generation of turbulence. experiences no other external forces. We wish to the magnetic field lines are fro/en in Ihe gas. and establish fa) the critical external pressure p^.. which there ts no rotational sheer). The continuum opacity for slowly tncteasing pc marks the onset of instability 214 A V «INTMUKUI jpitKi cont taction in the Mibcloud. Ihl the >table Tins is the fusi tesult winch we require The stale «I equilibrium configurations ol the suhdoud wlm.li oh- the suhcloud is determined b\ (M.m.T^vYcAt» lam when pc *- peL. anil their relaxation times Once wheic ilie tasi three ate simply dmicnsn nless mea Pe > pfL.. the su be loud lapidlv approaches f tee-tall sures ot the tuibulent. magnetic, and centrifugal ener collapse, unie» - or unul - centnlugal pressuie be gy content We note in passing that by combining come îniportani. The subscript V denote^ quantities equation )M and Inequality (81. we obtain the tin"I measured at the onset of insMbtliU. ing relations In order to study the stability ot the suhdoud. wr firsi consider the energetics ot ils individual mode* :».(.;*; Ki/ti ^„i < 10 n:i under a Mnall displacement. R - R' = RX = Rt HdXl. d\ « 1. wnh pf constrained to he constant The |bi We now wish to determine the stable cqmli- ihermai kineric energy h^0 = ,'MkT 2m, arid Hie mt- bnum indu Rlpfl to which the cloud will telav il hulen! kinc'.ic enerpy tj(, = ^.fcj,,,- are both invari Pe quickly the subclnud responds to changes in pc. We write the equation uf motion in a dimensionlcss form by introducing the variable i= t/tj-, where it = 1/î A < Sd+J'oVS (81 BGM(-m/5kTÔ) is the liec-fall time from equili brium: For the selfvaviuiional energy we note the general X = odu/dX nX/X3 (15) relations: a = **ltâ E^(R> = -3GM1 /5R =#E = ko n = {3kjcG1toH-5Gl2)inikV2m)in (16) 3 Re = - 2GMm/5r?ckT (10) term due to radiation pressure, which can be ignored during the CFS, but becomes important later (phase I C). Relaxation times for infinitesimal displacements Pec =f3(l+Jo-J£cJ/M J from equilibrium ire given by: (-S^G)3 (kT/Zm)4 (11) STAR KJRMATION 4 < ONTRAfTION/fRACMfNTATION PROBUMS Relaxation time* for riite displacements ire *-vaio- alednumentj)'• *> THE NUMERICAL RESULTS The import an i results are contained in dimension- lew quantities (X.C.r,). which aie themselves expres sed m terms of ike tliîmnutinlcss païamefen which specify the subcloud invariants tfo./i'çj^) and the external pirssure 01. fn this nutation, the results are conveniently independent nf (M.m.T). To faciliiatc tompansiin. we normalise the plot led quantities l0,X,r,> so that unity corresponds lo the value at the onset of collapse for a subcloud <*aÛiJ = H = Ac Q c *r: = 0. We distinguish these quantities by a superscript The normalised equilibrium subctoud star ('las. radius X*_ as a function of the normalised m external pressure 0 . for tf( =,\c=0. and 0' =ftl *>o b>< ^/J)»; % * 0.0,0. i,0.3, as labelled both scales logarithmic. X* = .lX/2t? (18) Figures la - c show quasr-equiiibrtum evolution ary paths - as characterised by the normalised equdi- brium radias XJJ - for prospective subdouds subjected to increasing external pressure 0*. up to the onset of exothermal instability against contraction 1&*XJ). The evolution is uniquely determined by (/"^ r%Jfy- An increase in J'giFiji. U)increases££ and decreases XJ. The same increase in r^fc (Fig. !b) increases &* slightly less, and decreases XJ slightly more. The Figure lb. As Is. same increase in ^c (Fig. Ic) increases&l substantial 0,0,0.1,0.3. as labelled. ly less and decreases X£ substantially more. In the context of condensation, the consequent delay in the onset of instability is compensated by the comparable tJ'tf.Jl) valves in Ihe parent-cloud, and their effect on the rate of change of 0*. In all cases, the subcloud has a large density contrast Ce ;> 3 at the onset of instability. Ffguie 2» (solid lines) shows a scries of ihe uUl'.X") curves which control > subcloud having 3Q~ //C = XC = 0. •* *** external pressure fr* ehan|«. The curves terminate at the zero contrast radius X*. which is the extent to which the subcloud must expand to have the same density as the back ground: the dashed line 1 is the locus u(0*;X*). The dashed Use IC is the locus of the maxima « O'lXg,}, which separate the stable equilibrium states from in Figure Ic, As la. except % = He = stability. Since the radiaûja pressure damping Is 0.9,0.1.O.S. as lebe&d. 216 AT WHITWORTH pn'bahK negligible, w* note the possibility ot pie- instabiun 1m ,i* > O.o-l this not onl> advances ihc onset ot instabilité. hut also increases ihc contrast on the onset to t_. where (\.< ('„ < 1(1 The dashed line t([ ts the potential curve uIS(X*l corresponding, to free-fall ai the onset of instability we note the divergence tel wren uls(X"t and w^*=l_\*l 1-icure Tr> (clashed line» is an enlaigemrnt »! the ul,J*=!l P^.,\*l curve from l-igure _a in the vicuutv ot t-ouilibnum. The solid lines aie lelavuimn times rI4(i*.X*) for displacements tiom equilibrium within the potential well (Xf^.X") l*e have considcied two damped cases. ij= 0.5.1.0. hut only the undamped case, rj = 0.0. is relevant to the suhvequcni dis cussion) We have also marked iheavy bar) tlie iic-e- 1 lall time of the parent-cloud T*pl^'l= 1(0* I"*- In- */*? less the subcloud is super-compressed. X—Xm. we have 7j(^'J£*l < rfLt^'l. so the sub-cloud must res Sfltd nines dimcnsionless piitential pond quickly (o changes in the external pressure cJ3* curia ulfl*:X*l as a funci urn of the The general validity of this statement is con normalised suhchud radius X'. for a sub- firmed in Figures 3a - d, where we plot r*0h3'l = cloud wilh f„ - Hc= /c = 0. and for rftf'JÇl. T*liff*)= TrV.X;i and rty$*i agatnst representative values of the normalised the external pressure p*. for subclouds with (^(V ^. external pressure 0* (as labelledf. Dashed ^t-l= (0.0.0.0.0.01. (0.3,0.0.0.0). (0.0,0.3.0.0». and curvet: I. locus uffi'.Xp. where X* is the (0.0.0.0.0.3). respectively. The relaxation lime for zero contrast radius: It. locus of the infinitesimal displacement T*0 is representative until maxima u(tS*,X„\t)i HI. potential function ff*-{Sç. when r^j-00 necessarily. In this limit, the relax UfjfX*) corresponding to free-fall at the ation time rtl for displacement to the zero contrast onset of instability. Tfic .V" scale is loga radius X*. û a more meaningful measure of the sub- rithmic. cloud's ability to respond lo increases in p"*. The free- fall collapse time for the parent-cloud is an absolute lower limit to the time-scale for appreciable changes in $*: in all cases, T*, < r?_. Consequently, instability against contraction can not be appreciably delayed beyond the instant that £*=££, and may be somewhat advanced by pre insta bility. The contrast Cc at the onset of instability is given by Equation (6) and satisfies the limiting rela tions (12): the contrast Cp at the unset of pre-in- stability satisfied the limiting relations Cc < Cp < 10. so that all subdouds can. in principle, become un stable with C= 10. Unless - or until - centrifugal pres sure is important, the subcloud approaches free-fall collapse (or magnetically diluted free-fall collapse; on a time scale which is shorter than that of the patent- cloud by a factor ~C^(i.e. 1.41 to 3.16). and con densation is highly efficient. If centrifugal pressure is important, a meaningful discussion must include departures from spherical symmetry. Contraction of both the subcloud and the parent cloud is impeded in Figure 2b. Dashed curve; a typical potential curve the two dimensions normal to £2- The condensation from Figure 2a. u(&*-0.666;"*}. i" '"* problem reduces lo a competition between two vicinity of equilibrium. Solid curves: re dimensional contraction of the subcloud normal to laxation times rf(X*) in the potential il. wluch necessitates loss of angular momentum; and well for TJ= 0.0,0.5.1-0. as labelled: X* and T" scales are logarithmic. STAR lOttMAHON i, CON-tRA^TIONfi-RAfiMfrMATlON |*KUt>i>M5 217 figure 3a. S'tUti iiiTvc. normalized relaxation times Figure 3b, As 3a. except J~0 - Tr , ()"r displacement tn the :cn> nmtrdsl radius Xp, as a functnm of the notrmi- ised external prtrmire $*. fttr a mhdnttd. **"'« JT, = l< s Ac = n- Hesheti etme. free-fall time fur the parent-ctniid jfp. •~i>ih states are tttgan: irar. «fie-tfiincnsiimal fijttemrsg o!" (he parent-cloud paral figure Jc. As 3a. except Hc = Q. 3 lel w> £i. which may milsaHv approach frcc-fïïl. bui is eventually halted by pressure gradients In this regime condensation is probably inefficient, in the sense thai an unf ragmen ted patent-cloud fim fhtiens to a disc. condensation then occurs on a lunger time scale determined by the efficiency of the processes which remove angular momentum (e.g. magnetic braking, density waves I. Huwcver. if subcleuds have already condensed oui substantially when the overall con- Iracnon of the parent cloud is halted by centrifugal forces, gravitational/kinetic energy is preserved, and the system does not flatten appreciably (see below). Figt&e 3d. As M except J(c = 0.3 7. CONCLUSIONS flic important result is Ihal. unie» centrifugal large -5û ~p - whenp/p0 -(p. '6p0y\ This result in pressure is important, condensation is efficient, be itself was questionable, since the first-order analysis cause prtepective subdouds establish themselves as could not legimatdy he sxtesded so far. bat 3 later such, beforr they actually become unstable against evaluation of second-order terms (Hunter, 1964} contraction: following instability, they (hen tend confirmed the conclusion. Nevertheless, the choice of tapidly io free-fall collapse (or magnetically diluted 5po/p0 remained arbitrary. The analysis offered here free-fall collapse) art s time scale much shorter than seems more realistic, particularly in the context of the time scale for comneiion of the paient cîoud. the Hoyîe CFS regime, firstly since it includes pres We first compare this conclusion with that of sure, and secondly since H derives useful constraints Hunier |1962|. who applied first-order perturbation on 6PQ/P0 which .ire valid before the medium be amlysii to the gi-owtJi of subcondensations in a free- comes prcssureless: namely I ^op^/pg^ 9; this sug failing, p£es$u'£tess patcni-cloud. He concluded that gests that perturbation analysis is inapplicable. if the initial density in the parent-cloud was*i0, then Of the various multiple stellar systems observed j small localised enhancement bpn would grow to be only one group, galaxies, contains obviously flattened 21S A.P WIUTWUttTII members. By contrast, a wide range ol multiple stelbi In the context "1 contemporary population I Mat piMems elliptical galaxies, globular and gala»in- ejus formation, the apparent lack of markedly flattened 01 Ins. OB and other loose associa linns - ate tint tightly bound system* places even more severe eon- markedly liai in addition, vine ol the smallci sys -tiaint- up'>n ihe «indentation efficiency II seems tenis appear In be onli weakly bound, tf ar jll li unlikeU that ptolocluster clouds have negligible 1 , wmk reasonable :o inieipiei these ptopenies. at K-..-t 1 although low pitch-angle collisions with a trailing partly, m terms ol the preservation ot gunialional -pual \hi*k nuy tend to reduce L£> We therefore kmrtiL energy against inelastic elision lossr-. jm! iev]uiie that when centrifugal force*, hall the overall ilns immediately places constraint- un ilir oMidcnsj .nnirjtitnn the IT'S lias advanced fast enough to cre Hon efficiency ate ilie lime lag necessary tor the realisation and tte surmise that galaxie- formed 'nm: primeval solution nl the localised centrifugal problem H\ wit- ptotogalacnc c)oud( basing a di-pet-ioii in -pevific pan-on nub the ptologaljitic cloud, the ptoto- anguh -momentum \i a L^.M.jnd mass M. and that Justei „ loiul nuy be at a disadvantage in cteating «his dunnc the ejrfy crapes before centrifugal présure-- time lag. it H lus undergone (ewer fragmentation became important, the OS advanced upidh. due to Magvt However, this is compensated l>y a giejlei con efficient condensation Consequently, the -nullest densation ctliiictKy. since the Lontcmpoiary gas subclouds realised the» centrifugal problem and ..-if- and n-n-iiihiiics throughout (he cmh -tapes »l could start to solve 11. before ccntnlugal loice- ha.! ihr ( IS iKl mi -Il • U, -ee ligation I :i thereby amplified sufficiently fo halt the overall coiiiuiiion advancing the "ii-et ol instability jl eat.li level, whilst at R - 5LJ CM In this scheme spiral gaiaur- the Ifiemul and JicmiLal hjtu'ue ot (etc protogjbc lie formed from proiogaljctic clouds with laiget 1 ,. gjv JJ. tfi.ye» .11 I midi - (i. -ee Hoylc 1***1.*- until and 01 smaller Ms When centrifugal forces halted the heavy elements are injected following the tiisl geuci- overall contraction, a large part of the pas was ^tiN jlion ol star- l*Ae also note, therefore, that an early highly diffuse, having had insufficient time w <*i|ve generation of star- in elliptical galaxies might enhance Us localised cemnlugal ptohlem. Tins pas dissipated the Liindeusation etticicncy substantially) its £ia<. national kinetic energy parallel 10 Q. in m-;*». l-urthei in M gin mlo conttaction/ fragmentation tie collisions and flattened m lomi a thin Toiam.^ P'ffllerm would seem lo reuuiir the following, (a) A disc Such discs have been shown to be unstable to a mine sophisticated 1 ragmen latum model which at number ol perturbations, which includes ifie develop tempts 10 include departures Irom spherical sym ment of central condensations 1 of the Galacin. metry . magnetic h'aking ami flux loss, generation and Centre), bars and spiral density waves. During the fot- dissipation of turbulence, and variations of lT.ni): it mat ion ol the spiral galaxy, some more condensed may be possible to neglect rotational sheer and cen portions ol the gas avoided collisions, preserved ilien tral condensation unltl phase C. (b) A code lo follow kinetic/gravitational energy, and ultimately became the CFS. For example, we might evolve binary hierar the population II halo stars. Conversely, elliptical chy, in which at each stage the suhcloud mass is galaxies formed from clouds with small Lf and, or f Mj+i = M./2. and the subcluud experiences an exter laige M When centrifugal forces halted the overall e nal pressure p j i = P, ..where (Mj.Pjj) ate the mass contraction, the CFS had proceeded further -viz lo ( + : and internal pressure ol the parent-cloud: once the subclouds less massive by a (actor ~(M ,M<.I (ijtV S continuing contraction of the subcloud is insured, the ]f ) in proportion lo the whole galaxy : and most s parent-cloud translates to a binary system, and the of the mass was concentrated in subclouds which had subcloud tu a parent-cloud. The CFS should end in a already made substantia! progress towards solving single representative protosiellat cloud massM . (e) their localised centrifugal problem. Thus the initial p A statistical theory to predict a spectrum of prom- star formation rate was higher and left little gas for stellar cloud masses, Np(M„). In addition we should future generations of star formation; hy the same tike: (d\ theories for prtascsC and D, which predict token, the system preserved most of its gravitational/ what Traction of M actual!V forms the star, and kinetic energy, and relaxed to a mildly oblate spher p hence how N,{Mp) relates lo N,(M,), the initial stel oidal configuration. This picture seems consistent lar mass spectrum; and I. Aaisclli. S J.. Mtrnphvi. unj Spj-e Sti 13, .1:4 10 MeMel. L . {Jiian J ft„v. ,ii/m« .%.. 6. U>\ &. 2.C.amii..t,M-.. Aitmpliyi J )3H. ! 1)5011'>M| llMestel. I. A Spu/ei, L-. Jni . M .1. IbyasÏM. (' . Ann. K«'f «lithw. ti .-iimjpfti-j. 4. A\tnm. S.» 116. 50.t ( I'ddi 17! i !«»«.) 12 Sslpetet. t>.....|wn/pii>i J IZI. )f-\ i p*5t,| 4. Hoyle. F . Aur, DISCUSSION M HARWIT Yt»a have presented one particulari thermal energy imbalance 111 it ifus picture is cor- sequence of events Mut y*»u believe tan lead to Maii feci, then la) very simple genmrttiL ti moderations fdunaiiim. Can yuu estimate flow many utitet right1 show which basic configurations «it munt-n «is and now equally probshtc • sequences could he made up" fruguettc Held structure will, jnd *hich will not. In slum, how unique do you fe<*! your sequence is aîli.» the CFS lu piEKced further: fM very genera likely tu foc'' energetic and mechanical considerations theft show irm die CFS lends ultimately to produce configura- A l\ WHITWORTH: h is evident that stars do noti lions which will noi allow further fragmentai ion. thai t'oitn alter a unique pattern i»l event* The sequence these configurations ate. however, suitably disposed presented above is simply one possibility. It appeals tu contract to stellar densities: and that they must to me, because it seems tit offer a solution to a realis.- have masses equal to or greater llian typical Mellai tically formulated and topical problem: namely, whyY values. docs fragmentation stop, or can fragmentatiun bet stopped with piotostellar clouds having typical stelln» 11. HABING: The structure oi associations, a. masses? ! suppose thai the ultimate theory of slati given loi example by Blaauw {Ann. Ret. Attrtm. formation will be a compiehertsive theory of rnagne-- Astmphys. 2. -13 (lfl64)j.and die occurrence of tohydiodynamic turbulence for a fluid whose equai- clusters of clusters of compact sources, should give tion of state includes ail those interaction* betweeni some information on ihe larger scales in the fragmen gas, dusl ard radiation which arc relevant to the enor tation process. Can you derive useful information mous range, of density, tempcraiuic and scale involv'- from these observations? ed. 1rs !*•- rtt-sence of such a theory, one must hope to deri*e meaningful results by artifkniiy isolatingI A.?. WHITWORTH: The theory is still JI the specific interactions, and thus assessing their effec stage of modelling individual contraction/fragmen tiveness over a limited range. 1 have explicitly ex tation events, using a dimensionless notation. It is cluded second-generation star formation from my t hoped ultimately to develop a code which follows the scheme. The formation of stats in association would i CFS through, and makes quantitative prédictions for seem to require a contraction/fragmentation se comparison with observation It will certainly be quence, as a prelude to the first generation; and 1 I encouraging if there is some correspondence with the have limited my considerations to this phase. It does, scales of clustering seen in radio, IR and optical ob- to n.y mind, seem difficult to avoid the conclusion i servations of regions of star formation and young that magnetic and centrifugal pressures are rapidly i clusters. However, it may not be possible to make a amplified during the CFS, and that consequently they i detailed comparison. The radio and IR pictures are quickly assume the dominant roles in the gravo- highly selective; whilst the optical picture probably 220 \r *tiirwuKiii onU erneices aller the clustering ha*, ha.i lime to tc- ation .nul ionisation pictures ol Hie ccnlral () star, lj\ appteciaMy At the prevent time, uno iJti onl\ and. >n ><> s one external agency this distuption may Hole that iIn- Mruciures .'bserved appeal m be ,onv induce secondary stat lortnation On the latgc scale, paiiblr wiiti tin- broadest outline ol ihc iheot\ the continuing existence ol gaseous discs su spiral galaxies suggests lhai con temporary star tonnaiion is B BAIK K Have \nn any idej conceiting .«..i in vmc sense inclticieni (unless one invokes icplen ishineiH by in I all ol inicrgalactic mailer) Don 1l'»~4. IAI' Proceedings' has estimated tliat in MSI U' UHI1WORTH In ihc sen early su^ . A.P. WHITWORTH: When a < contemporary) H bLSASSHK: What fraction of ihe mass of the pru'nclusfer cloud starts lo contiaci. ils température protoclusiei cloud do you expect in go inio stars" may be as high as T *- 100 K. However, during the early stapes of the CFS. the increasing density n. and the increasing visual/UV optical depth r . enable the A.P WHITWORTH: This is a very fundanenlal v problem. On the small scale J. Mayo Greenberg & Scung Soo Hong Stale Uftiverûty of New York. Albany, and Dudley Observztory ABSTRACT The strength trf ihe 'J^jwi absorption hand in tent with variations in the wavelength dependence of the tadiatton from the Galactic C'entie is used in extinction 3i a function nf grain characteristics is in deduce a range of meatmes of the visual extinction dicated The mass of silicates deduced fmm ihe from 20 to 400 magnitudes A piissihle way of arm u 7 i/m hand apfx-ars to imply a gradient of metal- ing at a unique *3lue of the visual extinction CORSIS- iicst> towards the Galactic Centra 1 iNTRODLCnON Tlic question <>f the total visual extinction lo ihe follow this assumption i h rough to is logical conclu Galactic Centre is critical m discussion of the nature sion. of the radiating source. A value of 27 magnitudes was I'sing a model for interstellar grains which, at derived some time ago jBecMin & Seugebauer, 1968] least in oui neighbourhood, is most ;onsistem with an ihe basis of an assumed intrinsic energy specttum observations JCreenberg 4 Hong. 197.33, b; Green- of the Galactic Centre and an extrapolation from the beig. I374|, we find that the assumption of an aver differential reddening in the 1.65 • 2.2 am region into age exuiKuen carve leads to a vouai extinction in the visual at 0.55 fjm using a, standard extinction law excess of 400 magnitudes, which is quite at variance [e.g. Johnson & Borgjnan. !9t*3|. This had come to with the values proposed to date, in the course of be a generally adopted value and was apparently sup discussing the consequences of the result, we show ported by later utiservations by Spinrad et al. 11971J how it is possible to reduce the extinction, consistent and Borgman 107.1) at shorter wavelengths. Possible with ihe t.7 pm absorption, but tn so doing we arrive lower limits, down to 1S magnitudes or even 5 magni at the fact that the extinction must be far from nor tudes, have subsequently been derived or inferred by mal. Ii appears possible that a mutually consistent Borgman |S9?4| \a the other direction, a value of value of &nv may be derived by combining the near- 75 magnitudes was adopted by Ailken * Jon» infrared colour excess with the appropriate extinction curve. A number of key uncertainties remain, one of It is apparent that the situation is far from set them being the precise optical properties of the sili tled. In this paper we shall derive a range of measures cates leading (o the 9.7 fim absorption. Another is of the visual extinction based on the strength of the whether ihe silicate absorption occurs very close to 9.7 «m absorption bind. the Galactic Centre within 1 kpc- However, then re mains a strong presumption that the extinction to the It may be that the distribution of the dust provide Galactic Centre b> likely to be larger than 27 magni ing this absorption precludes our using the depth or tudes rather than stnajlet. and may be more consis the absorption as a basis for this extinction cilcu. tent with that of Aiiken & Jones |19?3j. lalion. But until proven otherwise, it is still useful to J M*\ ; THE 4.7Mm ABSORPTIO.N AND IMPL!fcl>SILICATE MASS IT-*- depih oî me jf'Mxptii'iî 41 « ~^t:i gives a specifu density of .* "gcni* I cot responding to oli inrj-me ol the ti-ial volume -'I situate maienal along vine I ihe mass is I N4 \ 1(T ' g-,V It should he die Urn* t-.t sight I,- the GaUwiw Cemte U wt assume. noicd that Woolt deuves a value ot 4 .' magnitudes JN [, undoubted!) true, lhji Hie sthcalc nuii-rial is tixm the wine data and Hoigman |l,,71l Muds a .iiuded iiiio panicles whose sue is much smillet than value ol 2 1 magnitudes liom his observations with a W^m It some ol the silicate patliclcs along the path sinallei apeitute He shall use nut irtetiiicdutf tr\ult a.-<- healed sufficiently to tadiate significantly at j\ a hase value and 1r> In estimate b> how mm.h tins lOjjm. then the observed absorption gives a lowet ma> be under or ovetcstimated ^ound "ii ili 3. VISUAL EXTINCTION TO THE GALACTIC CENTRE (n order lo use Ihe total mass of silicate material ment depletions (Greenberg & Hong, 1973a,b; to derive the extinction to the Galactic Centre, we Greenberg, 1974]. The component of the grains must have a model for the interstellar grains. Such a which is responsible for the visual extinction has been model has been developed recently to conform with, shown to be well represented by elongated particles among other basic observational features, the litest (infinite cylinder) with silicate cores of radius ac = data on cosmic abundance and interstellar heavy ele O.Ooum surrounded by modified ice mantles distti- UlSl IS I HI (,\l M'fU (IMXI z?.i hnk-tl m tadti atcordii;)! ju leifullcd mkulaiinm. we \tuli present an .lutitm: Wrc ot how they may be *.jriied HU.,,1 " <">r Is'"' ' >' I "I l lUtvc He te pie ten ted hy i!r.ijm.>) vthvie j,n ^ '! i- thai !ui 3 |3%eii ttitnti si/c. tin- ettcwiivc single variabfe pjtaroeicr Fix a calculated exiin. H>>n uirve r.hiajnr.; î.-i putpinev it! mass am! csiiTKln-n meaMiies use at - v«nt pven elfective mantk FJJIIK «re nuv .ïeltre Odd uni ami am - 0. ' * prti willtnul tonvdeniig M/I- dlMMlxitiont l-urThrim»rr. J'«»f simplicity "iir calculj- rail» rtainth> tnHi\ I mm line i-n are N>r spheres, hut n sl;.>uld K- ORI% tinted that a pntpei Aomnt ••! the etircts .it n..n ^n»>. t ^mtAii m spliertciiy inUmliHcs ufhei «ntall ch-iiiyf, in let us first «inp*n< that the triairts inward the where Hie C.IIHJI excess. Amt>:) Ami>, l. will V tiabclK Tenue ptudticr tmimal «tmctmn. The tula! obijined in the neai intiared. cf 1 am jnd .^m jt number oj such f>iam\ ts. nbtamed by .'ivulme the used by Bcckhn Sc Neuptbauer In te(mv "i the jb- 4 vKptitin m the <,3bc!ic ( entre J( " " am. we ^IM. total silicate volume, V'sl| - 4,'W \ Iff cm'/cnr.ny have the volume 'it a unfile one. I « tr at.' Ft (tally, -vc ithtsin the visual e\iincftt>n a* K Amv = I OWi I) J' C(.xln(amidjm Jmv= I (WMij [)0V ""'I',;, 0*c mt - J M» which may he written as = 4 (Hi { i a 3 t C r;, : D in\. * 1 08(Snt]Ov^m" m "" where J>= distance to the Galactic Ccntie. ac is in wheic the value a( njl) is simpW ja^cn h> «m. and Ov1"" " m* is 'be avciage or effective CXIMU- tton efficiency fact i IT in ihe visual for the core-man tie »J» J» V ïVsrl ,T* dust giains wiih effective mantle tadius am. For tlte grain parameters corresponding to noimaJ Combining Fquaiions (Si. (61 and <71. we obtain the exunciH'd, and lor a representative value letaiionship Irom which am may be derived t^tc ral= |.5iWC find ilm, = 406 magnitudes from FquaHon (3i At the other extreme, namely no tû 1 4 1.0K6Vj,t manllc* whatsoever, the visual extinction is obtained m 3 finm Equation O) with am = ac and noting thai the 0vram)am 3 W>il imfXilaj.' C efficiency factor is now. foi lite cores alone, 0V - P°r stlicaie particles nais Itttemherg. 1M~t|. all o] which ate proirsv. n-ived laipe numherv •>! molecules in the (.atactic itul aie j^icliruici S\ healing nl the grains Hits Centre could account for a nuii'T mnml-unon to the • >!'- 4. RELATIVE ABUNDANCE OF SILICON The column densit> >n average even in Uie solar neighbour• loim ol illume demed Iront Equation (2l i\ I h> \\ hood heiause of the existence >i[ a biper amour» ol 10 g cm: From tlm vi' mler a column density n•l I hydtngen in molecular lotm than previously csti vi/j..'n in the grams as N^, = <• 44 \ 10'*cm: It is mated Vie may thus ieduce the cak.ul.itcd relative not possible to ohuin direcllv the total hydrogenn abundance ol silicon to perhaps three time* the nor- column density to the Galactic Centre because we mal value. This remaining (actor may he an indication Jnn't have a good estimate ot (he amount in mole•- • ol a gradient 5. ACKNOWLEDGEMENTS The work described was supported in pan b> completed while the authors were visiting al the Insti- SASA Crani NCR 33-011-043. and the paper was lute of Astronomy. University of Cambridge, I. Aitken. D.K. & Jones. B.. Ap. J. 184. 127 ( 1973i. System. Proc. Nice Symp.. April l'>72. Centre 2.Becklin, E.E. & Neugebauer.G.. ,4p. J. ISI, 145 National de la Recherche Scientifique, p. 135. <1968). 1973. 3. Boigman, }., in Galactic Astronomy. Ptoc. 1AU 9. Creenberg. J.M.. Ap. J. 189. LSI < 1974). Symp. No. 60 (Eds. FJ. Ketr * S.C. Simonson). 10. Greenberg. J.M. & Hong. S.S.. in Galactic Astro in press. nomy. Proc. lAUSymp. No. 60(Eds. F.J.Kerr& 4. Bergman, J., Astronomy & Astrophysics ( 1973). S.C Simonson). 1973a. 5. Day, K.L-. Sleyer. T.R. & Huffman "I.R.. Ap. J. 11. Greenberg, J.M. & Hong, S.S.. Paper presented at in pre». the Dusty Universe Symp.. Cambridge. Mass.. 6. Grecnbeig, J.M., in Nebulae and Interstellar Mat November 1973b. ter (Eds. B.M. Middlehursl & LH. Aller), Univer 12. Johnson, J.L- & Borgman. J., BAN 17. 115 sity of Chicago Press, p. 221, 1968. (1963). 7. Greenbeig, J.M.. J. Colloid and Interface Sci 39. 13. Spinrad. H.. Licbert, J., Smith. H.E.. Schv.ei7.cr, 513(1972). F.&Kuhi,LV.,>tp.y. 165,17(1971). 8. Greenbe/g, Jjrf., in On (he Origin of ihe Solar 14. Spinrad. H., Smith, H.E. & Taylor. DJ., Ap. J. ('IN l IMK! f'ipuv ÎW IAI Sirnp V. <;. jfcjs 1^ Van de Huht, H< , Cuh! Rm,.i Ob- I V! (,reenherg A Ht van de Hul\U. 1> Rcidel 4.1 H'JMï ( AM)K1!SSI V.mi p. l jNuii thf depth ni H (llftMK tliC band JT Hinni m irljin [•• tlic jhundarur "1 «iujt<-\ m llict.^jvtK t .-titre rmi entirely, •.•imru .mid ihiN ev^ev h>df'prn he lijdUrci i me tot nie lu ••m .jkubliiir e liiij liiai îhiiband thanpfs m depth depending un the temper aime tield and tiit demity Wwl ! dti n«<î umle f turn! the» i\ I MAYO <,Kt fcMjfcKt, h uouid hj« t.. he m hu» >i>u *jn iihuimoii the JIIW! in gtif,t!<<. I:ke Hie ioim »t Hi rïK.Kuies in order *<> be sfcS-.iîKant the lempcraiure tltfïti il"! Oie density and addtes* f Hhet rwdctilcs smuivmi smh elements a* i \ jud yl>^llvl^c^ i t Bftkliii & <. Ntugebaurr Hate »tr-er*amriev iaiiiiinsa Itotitutc of Techiwtitfjj? < amrgw Stiviitiiiiot) ni Waxhiftftfitfi D Earty California Institute of Technology A new ' I um nupilig 11 m Tin- (i.ibciiL {/time Hum indu-ax-cmion lintt icani »n ihe 1 m T-lfunpr ft£nm \x&\ been iitiJc oser a 1"\ ]** Mm wild an aî IJ> Cjmpanas. (Iiiic «sing j convcntionat phtttti» angubr r«$uhition of \.Z' Tlie tiwp was construe: eil iwwi L'nlike previous maps, ihe present tbia »cir Figure i. -« 22 ftra wp o/ the central 1° of the Galactic Come in the form of a video picture. The intensity shown is essentially linear with flux, pie peak flux from the centre of the Gglaxy lias been truncated at 1/5 the observed level. The angular resolution is 1.2', ! I BIlKUV U M t i.iHAIIH A l> I \Rl \ obtained *iib IMIK a \mide mcjsunnj; beam, itic /eto tu'ii i lu't clore also it'Ilea s the mass dtstrirnilinn le»l?J OÎ lilt IIUp *3S Ukeil J* the JiefSKe llliX I" f Jsl S.me CM.ICMCC tin daft dusi clouds can he seen and weM ot ".lie (.jLiciic ( enire throughout the imp including the area around Sgr H; The new map açtees. with the m*wc limited map which » ttoithem oi the fiabcin- t'eitiic. fheic ol Bcklm A. VujrerMiiei |l«t>S| the hughiest pot appears ii' lu' no evidence ol a dark cloud near the non ol ihe (..atactic Centre aica i* legated JI the pusi- hnghicst portion nl the map. This result \f> supported linn >>i the radio si'UW Spt \. ar.d i\ clcarh dun h> limned wans at I.(»5 j/ni which indicate rhat over £4«J jioiiii ihe çaïjclic plane Hie ' 2#m ladutio» the «eritial lew arc minutes of the Gahciu Centre ilir proK- ACKNOWLEDGEMENTS We *ould like to thank the stall ol the Las Cam- National Science 1 oundation (Giant GP 3S545X)ami panas Obscnaion. lor then hospnahiv. and especially the National Aeronautics and Space Administration Messrs A-Zuniga. A Guerra. LPapic and M Wagner iCtjni NGl 05-(ll)2-207t Financial support tot this work was provided hv the REFERENCE 1 Becklm. fc.fc. & Neugehauer. G. Ap. J 151. 145 DISCUSSION V. PETROSIAN: Whai is the accuracy of tlic dit- ation is similar to the observed radiation between 40 icrcnital extinction estimates'' and 300 urn in (he same region. ht. BECKUN Probably to a factor of 1.5. D. LEMKE: Can you give the total 2.2 pm flux as integrated from your large map? Would you expect C. ANDR1ESSE: Would not the presence of the an extended source at the Galactic Centre if you look dust lane, which is visible just east of die bulk of the at it with an 1 " beam and absolute chopping? 2.2 tJm radiation, affect the position of the maximum brightness at 2.2pm' Is i! possible that this explains E.E, BEt'KLIN: i do not have the answer to your the difference between the positions of maximum first question, but the answer to your second ques brightness at 2.2 and 10pm? tion is yes, it is clear from the map. E.E. BECK UN: The maps are on a completely J. BORGMAN: For total extinction at 2.2 *mi by different scale. There is no indication of a gradient dust in a centra! H II region, one would expect that in the absorption which could move the position of there should be a 0.7 mag. 'hole' in the 2.2 Aim distri the 2.2 #m peak. bution. Apparently you do nol sec that. Can one make a realistic estimate of the extinction on the R.E. JENNINGS: Would you picase discuss the basis of the observed 10 - 20 fim radiaMon? relationship between the shorter wavelength 1R sources and the far infrared source at the Galactic E.E. BECK LIN: The extinction within NGC7027 Centre? is only about 0.5 magnitudes at visual wavelengths, (0.05 mag. at 2.2^m), yet almost all of the Lya E.E, BECKUN: From about 3' to 30* diameter, radiation is converted into 10 - 20 fim radiation. the stellar luminosity deduced from the 2.2 ^m radi* J. BOKGMAN. J- KOORNNfclT & M. do VRll-'S Table 1. flw«'n of domuuini infrared sources Reference RA Titis paper 17h42m29.59s+0 irjs -28°59'19.3"+ 1" Rieke & Low 11973] 17 4: 29.45 + 0.15 - 28 59 17 +2 Burgman 11Q73* 17 42 29.70 +0.15 -28 59 19 +2 Ekcrsetal. [19741 17 42 29.50 +0.10 - 28 59 22 + 3 with ilic peak located at the co-ordinates in the first Downes & Martin (1971 J. Tlie agreement with th* line of Table 1; the corresponding galactic co-ordi- infrared position derived here is within (tic combined nales are 1 - 359.94°. b =-0.05°.Tlic agtcemenl with uncertainties and wc suggest that the compact radio our earlier détermination (Bor^Tian, 1973] is quite source must be identified with the dominant 10 - satisfactory, and there is also good agreement with 20 jim source. It should be nulcd that the other infra the results of Rieke & Low 11973J *. The last line of red sources in Rieke &. Low's 10.5 pm map are well Table 1 gives the 6 cm radio position of Ekers et al. outside the error box of the radio position. In (ho 119~-,} : this position relates to a sharp maximum of following discussion il is assumed thai the compact the 6 cm continuum flux, very likely corresponding radio source has a thermal spectrum. to the compact source in Sgr A West, described bv 3. THENATUREOFTHEDOMlNANT10-2<>pm SOURCE Figure 2 shows the spectrum of the source. The observed 3 - 25 pm brightness of the dominant 10 - 3.7 • 12.2pm data have been measured with a 7" 20pm source which would be observed with a 7" 10 1 diaphragm. Unfortunately, in the far infrared there diaphragm to be 1 x Iff W/m , equivalent to 5 are no data with the required angular resolution; scal 3x 10 LQ. The total infrared brightness . • be ing down to 7" of the available data (Harper & Low. slightly larger if the far-infrared radiation unexpected 1973; measured with a 5' diaphragm) is rather mean ly shows an appreciable concentration. ingless. At 1.6Spm and 2.2 pm we have taken the 7" In relation to our claim that wc have resolved the diaphragm data interpolated between the measure dominant 10 - 20pm source, ii should be pointed out ments of Becklin & Ncugcbauer (1968) which relate that the scans in Figure I indicate a sharper maxi to the point of maximum flux density at 2.2 um. mum than expected from a flat-topped energy distri However, this point is displaced approximately 4" to bution. Further, the cxtenlion in RA. though be the west of the dominant 10 • 20 fim source (cf. lieved to be real, is only little more than is expected from a point source. Our instrumental resolution is Becklin. this conference), which means that tire diffraction limited and is inadequate to resolve fea 1.65 pm and the 2-2 pm data -mist be regarded as tures smaller than 2". upper limits. The same holds i 22" diaphragm data at 1.08pm and 1.18pm from Spinrad ci al. Wc will now discuss some suggestions on the (1971). Adopting a flat spectrum between 12.2 and nature of the source; the discussion is based on a comparison with known classes of luminous infrared 20 pm [Rieke & Low, 1973], we find the integraled objects. * Rkke Jl LOW state that they have corrected their decli nation foi 2" cWerenlûl (V - 10.5;») atmospheric re fraction at an elevation of 30°. According to the refrac 3.1 A COMPACT H il REGION tion utile and formulae of Pcimdorf [1957], um should be 1.3 , which tends to improve the agreement with our The spectrum in Figure 2 is reminiscent of the value. spectrum of W3 (Wynn-Williams el al„ 1972] and DOMINANT 10 - M fia SOURCLS IN GALACTK" CKNTRh A seen non fW50t Figure }, Scans in RA (decl. -28* 59' 18.4"} and declination (RA f Off -28"SÏSÛ" Declifiotian (1950) shows ihe characteristic features of several mfrared- figure Z The spectrum of the dominant 10 cmiuing H 11 regions: at 10-?Ouman infrared excess 20 am source (solid circles). Vie four is observed two orders of magnitude over the Dux points, connected by the full drawn !he of the ionised plasma (as extrapolated from the radio lave been measured with a T circular fiux). in the near-infrared, even ihe upper limits plot diaphragm ai the position of maximum ted m Figure 2 are lower than the predicted flux, 12.2 pm flux density. Vte S and 20pm conftrmmji tiie presence of appreciable absorption. points apt from Becklin & Neugebauer Tlic observed 3 - 25 pm luminmity is significantly i I969f. Vte 6 cm flux density las been larger than would be expected from the absorption of taken to be 2Jy IDovmes & Martin, LQ photons by the dust. Tliis may indicate that a 1971; Eken & LyndenBell, I972f. The large fraction of Lymart-contintium photons is direct other points are discussed in the text. For ly absorbed by the dust; in alternative suggestion is comparison, the spectrum of W3 (AI tliat the source contains unresolved non-ionising 1RS I has been plotted (open circles and infrared components. dotted line; data from Uynn-Mlhams el The compact H II région may be embedded in a at. 197J). larger H II region, coinciding in position and dimen sions with the thermal source Sgr A West as well as temperature at 12-2 Jim of 100 K in a dtaphngm of the more extended 10 - 20 ym infra .adtatiort. The T\ the corresponding optical depth is 0.031. The (8.1 - 12.21 colour temperature of the dominant colour temperature varies between 200 and 270 K 10- 20 pm source is 270 K, compared to a brightness over the are* occupied by the extended 10 - 20 pm 232 J. BORGMAN, J. KOORNNKEF A M. radiation [Borgman. 1973). We suggest that a con 3.3 A PRESTELLAR OBJECT siderable fraction of the excess emission at 34 pm |Sutton et al.. 1974| as observed in a 30" diaphragm Wc will compare some properties of the dominant should be ascribed to the cooler dust immediately in 10 - 20 pm source with those of W3-1RS5 and the front of and behind the extended 10 - 20pm source. BN object in the Orion Nebula. Each of these ohjects shows the 9.7 pm absorption feature. However, the two comparison sources have the 'stellar feature* of 3.: A PLANETARY NEBULA being smaller than 2" in diameter and are associated with OH and HjO emission, whereas there is no radio The shape of the spectrum in Figure 2. including continuum emission.. In contrast, the dominant 10 - the supposedly flat radio spectrum, is in good agree 20 pm source is genuinely extended (4" x 6"); there is ment with the spectra of sorrw planetary nebulae no molecular emission in the immediate vicinity; (he JGillett & Stein, 1970J; the 9.7 pm absorption fea 9.7 pm absorption feature is probably not associated ture in the Galactic Centre is unknown in planetary with the source, hut with dust in the large cloud of nebulae, but it has been shown (Bergman, 1973| that cool stars; and we have identified the source with a this feature probably arises from absorption outside compact radio continuum source. It may be that wc are observing an advanced stage of evolution of one the space occupied by the 10 - 20 pm source. The s or more massive protostars, which have become suffi observed luminosity (3x 10 LQ) is, however, ai ciently hot to ionise the compact radio source. least an order of magnitude too high for a planetary nebula; several, probably at least, 50, would be need ed which makes the suggestion unlikely: even a num ber ratio of solar masses lo planctaries as low as 10* would require a mass concentration of 2 x 10* MQJPC3. 4. CONCLUSIONS On the basis of the present evidence, we favour an roughly with Sgr A West. These hot sources of dust explanation of the observations of the dominant 10 - radiation are superimposed on the much more lumi 20 pm source in terms of hot-dust radiation; the dust nous and extended source of cool dust, healed by is locally heated by O-sUrs ot protostars which have lale-stars; this source radiales predominantly at XX become hot enough to ionise the hydrogen in the >50pm [Bccklin & Neugebauer, 1968; rediscussed vicinity. A similar mechanism, leading to somewhat by Borgman, 1974| and causes the 9.7 pm absorption lower temperatures, may be valid in an extended feature. region of JO - 20pm radiation, which coincides S. ACKNOWLEDGEMENTS It is a pleasure lo acknowledge the efficient sup- prior to publication, ihe improved position of the port of ESO's svafT during trd» procnm»e. We compact radio source, are grateful to R.D. Ekers for making available to us. 1. Becklin, E.E. & Neugebiuer, G.. Ap. J. 151, 145 It J., Astron. Asrwphys. 29. 443 (1973). (1968). 4. Borgman, J-, Proc, IAU Symp. No. 60 (Maroochy- 2. Becklin, E.E. & Neugebauer, G.. Ap. J. 157, L31 dore), in press. (1969). DOMINANT 10 - M Jim SOURCES IN GALACTIC CENTRE 233 5. Dawnes, D. & Martin, A.H.M., Nature 223, i S 2 Î0. Peraidorf, R..JOSA 47. Î67(Î9S?Ï. (19711. 11. Rieke, C.H. & Law,FJ„Ap.J. 184. 415(1973*. 6. Ekers, R.D., Goss, W.M., Schwartz, U.J., Dowries, 12-Spiruad, H., Liebert, J., Smith, H.E., Schweiicr, D. & Rogstad, D., to be submitted to Asiron. F.&Kuhi, Vf-.Ap.J. 165,17(1971). Astropiiys. 13. Sution, E-, Becklin, E.E. & Neugebauer, G , Ap. 7. Ekers, R.D. & Lyndcn-Beii, D., Auropfi. t.tlt. 9, J., in press. 189(1972). 14. Wynn-WiLiams. C.G., Becklin, E.E. & Neuge S.Gilku, F.C. & SUin. W.A.. Ap. 7. 159, 817 bauer, G.MNKAS 160, Î 0972). (1970). S.Harpet, DA. & Low. F.J.. Ap, J. 181, 781 (1973). DISCUSSION D. DOWNES: in your comparison with W3, d0o positions of bright stars which are about 4' away. the IR spectral points refer to the whole 20-30i"" First, we aligned the cross hairs in the eyepiece with ares, or only to Rieke & tow's source no. I '' the infrared diaphragm by observing a star in both che visible and the infrared and then we went to the near- 1. BORGMAN: The 5 - 12 Jim points in Figure 2 by visual stars. A giid of stars was in fact used to have been recorded with a 7" beam. ensure that there was no distortion in the scale. C. ANDRIESSE: How real, from an observationall J.A. FROGEL: Do you have any reason for sup- point of view, is the distance of 4" between the posing that the lOijm source is actually very dose to centres of the near-infrared source and the dominanitt trie centre of the Galaxy, rather than anywhere else lûff m source? along the 10 kpc line of sight? J. BORGMAN: It is near the limit of what 11 J. BORGMAN: There » no lOrwn survey which weald be inclined to place confidence m; Seckîifiit shows that this is a unique source m the area. Quit* a finds that the centre of the 2.2 urn brightness is dis5- number of people have, however, looked at larger placed 2" to the west of the dominant i© - 20f*mTÏ areas than this particular one and we can say that this source. source lies within 2' at least of the dynamical centre of the Galaxy, although the error in that is also of the D. LEMKE: The positions of the infrared source•ss order of 2*. The source also coincides with the radio you gave look very accurate. Against what reference maximum so that, although there is no absolute were they determined? proof, it would be unreasonable 1 think (o assume that this source just happens to be in the line of sight. J. BORGMAN: We derived them from published 235 MULTICOLOUR FAR-INFRARED PHOTOMETRY OF THE GALACTIC CENTRE REGION H. Ûlthof Kapteyn Aslronomical Institute. Department of Space Research. University of Groftingen, The Netherlands ABSTRACT Results ate presented of far-infrared photometric simultaneously, during balloon flights conducied in measurements of the Galactic Centre region. The ob- the south of France in 1972 and 1973 m co-operation servations have been made in two wavelength bands with CNES. I. INTRODUCTION In addition to our measurements on galactic H II length bands simultaneously. The ratio of the ob regions lOHhof & Van Duinen, 1973;01thof, 1974). served fluxes in both wavelength bands is a function the Galactic Centre has also been scanned. Our aim of the emission mechanism of the radiating medium. was to observe the far-infrared emission in two wave- 2. INSTRUMENTATION The detection system consists of two separate aBows the sky to be scanned through 26° of ele photometers mounted on the cold plate of a helium vation. The gondola itself is oriented by means of a cryostat. Each photometer contains a field dia servo control system that senses the local horizontal phragm, fQier, imaging mirrors and a gaWum-doped magnetic vector of rJtc Earth as a positional reference. germanium bolometer. To select the frequency band, The stability of the servo system is about 0.5°. The use is made of the «ststrahîen reflection principle of skleriai motion gives rise to a series of scans at diffe crystal materials JWijnbergen et ai, 1972]. Each rent hour-angles. 7r.-. offset of the magnetic sensor photometer b fed by a 20cm parabolic reflective f/5 c 'n be changed in both directions on ground com telescope observing off-axis. The two telescopes are mand, thus allowing repeated observations of the mounted vertically in a balloon gondola and look out same celestial area during a single flight. The cooled ward via a rocking flat mirror. A 13° rotation (step aperture stop restricts the lull field of view to 30'. ping motor) of the flat mirror about a horizontal axis Flight altitude is 4.7 mbar. 11. OtTtlOi- 3 CALIBRATION The final results of photometric observations de Jupiter in the two bands gives a brightness tempera pend on the calibration of the instrument. Absolute ture of 140 * 5 K for this planet. This value is m good .jlitrjuoi] H. usually hard lo ad-' ;e. In infiared as- agreement with the results of Annann et al. 11969) iionumv. plar.els have been uscj ainsi often as in- and ArmstniMg ct al. (I972J and will be used in the iiicht calibration standards. A comparison of the further analysts of the dal j. infrared signal as observed fioin the planet yields the The noise equivalent flux densities observed dur observed energy provided that the output of the plan ing the flights were of the order of 2 x 10"" Wm"1 et in ihe appropriate wavelength range is known. To H/"1. This corresponds to a detector noise-cuuivaleni- check the consistency of the results, an attempt has power of 2 x ifJ1IW W?;'-, which is considerably been .nade to calibrate the photometers in ihe labora liiglier than might be expected from Uie detector spe tory. A vacuum collimator and a ihermosiated hlack cifications and the background photon shot nuise body have been used to determine the output of the contribution. We attribute the excess noise to the ef photometer in the relevant wavelength bands. A fit of fects of mechanically driven parts in the gondola. the laboratory calibration with the observations of 4. OBSERVATIONS The results reported here have been obtained dur Some examples of the transmission characteristics of ing flights on 6 June 1972, and 7. 16 June and 2 July these bands have been published earlier by Wijn- 1973 from the Tallard balloon-launch facility ope- bcrgen el al. 11972J - Several scans have been made lated by the French Space Research Organisation through the galactic nucleus with a 0.5° beam. By < CNES). The performance of the balloon gondola was using the position informati'in from the scanning mir satisfactory, except for oscillatory motions m both ror, the azimu'h error from the servo system, the azimuth and elevation. The character and amplitude time recorded simultaneously with the photometer of these molions varied during flight. Reducuon of output and the geographical position of (he gondola the observed signals to an intensity distribution across during flight, each signal obtained is transformed to the sky is complicated by these residual oscillations. celestial co-ordinales. Owing to residual pointing er During each flight, observations were n ade simul rors, the signals show variations in amplitude in diffe taneously iniwo wavelength bands, shown in Table I. rent scans. A statistical analysis of the signals led to the results shown in Table 2. Unfortunately, the ga lactic nucleus lias not been observed ii the 30 - 38um band during the flights 1973 1 and 1973 111. Due to electrical problems, no results were ob tained in the 30 - 38 ^m band for two-thirds of these Fligh! Wavelength bands. *im flights. During flight 1973 III, no reliable results for the galactic nucleus in this band were obtained be cause of the high noise level resulting from degrada 1972 71 95 84- 130 tion of the system. For the 71 - 95 urn band, an 1973 1 71 • 95 30- 38 average has been taken for the flights which included this filter. 197311 71 • 95 114. 196 1973 111 III •154 30. 38 5. DISCUSSION Due to the large beam and the inaccurate pin contributions of the individual sources in the galactic tional information, it is sol possible tu separate the nucleus. The values given in Table 2 are averaged MULTICOLOUR FAR 1R PHOTOMETRY Ot- GALACTIC CKNTRI- Table 2 Wavelength band, Aim 71 .95 84-130 III-154 114.196 Ralio with Jupiter 0.57+0.12 0.94 + 0.14 0.94+0.23 1.19 + 0.24 Flux, 10' »•" 6.2 + I.J S.9 + 1.3 3.7 +0.9 5.8 t 1.2 Flux density. 1011 Wm"1 Hz"1 5.S } 1.2 7.1 + I.I 4.9 + 1.2 5.4 + (.1 Intensity. 1011 W m" ' H*1 si"1 9.7 * 2 12+2 8 +3 9 +2 14 Tb. K 19 16 13 observed fluxes in a beam of 0.5° centred in the ga that the flux is constant over the beam. This is a good lactic nucleus. By dividing the indicated fluxes by (lie approximation of the intensity if the source is larger frequency content of the spectral bandwidth, assum than the beam. For sources smaller than the beam, ing the flux to be constant over the beam, we can one expects a reduction in the flux per solid beam calculait the intensity pet unit solid angle and (he angle by going to larger beams. We see good agree corresponding brightness temperatures (Table 2). A ment between the results of Hoffmann et al. and decrease in brightness temperatures is apparent at Harper & Low. The results of Aumann & Low are in longer wavelengths, a phenomenon that can be ex conflict. With comparable beam sizes and chopper plainer "*y temperature gradients in the outer, pos throws, Hoffmann et al. [1971 a) conclude a size of sibly cooler regions of the source. These outer regions 38'x 15' for SgrA, while Aumann & Low (1970] make ar irtant contribution to (he (luxes at conclude that the diameter of the galactic nucleus is less than 3'. This last conclusion, however, is not clear longe lis. fro... their published data. C of our results with those of other author ^mewhat difficult because of the diffe Our flux per beam solid angle is s.naller by a fac rences earn size and observational technique. Our tor 3, indicating that most of the energy emitted in scanning .jchnique with a large beam is more sensi this wavelength band originates from a region smaller tive to extended sources than the smaJI-lhraw beam- than our beam- Because of the extended nature of the switching technique used by Aumann & Low [ 1970], galactic nucleus, it is difficult to obtain a total source Hoffmann el ai. [1971 a, b], and Harper & Low flux. Our scans aver this region indicate an extent of 11973]. The small-throw beam-switching technique is at least 4° in galactic longitude, with emission in the insensitive to low intensity gradients. Table 3 gives a outer parts at about the 10% level of the values given comparison of the far-infrared data published for in Table 2. Probably the best value of the total source SgrA. flux has been given by Hoffmann & Frederick [1969] The flux per beam solid angle, given in the last utilising a 1-inch telescope with a 2.3° beam. column, has been calculated under the assumption Band Beam F„ fj/ro) (aie min) (10" ffm"' Hz"'j (10" Win"1 Hz"' sr"') Hoffmann el al. [1971 a.b] 80-135 12 33 3.5 Aumann & Low (1970] 40 • 350 10 80 12 Harper & Low (1973) 30-500 5 7.2 This paper 84-130 30 71 238 it oiTHOi 6 ACKNOWLEDGEMENTS These results would not have been obtained wiih- of this manuscript are gratefully acknowledged. om the laborious work skillfully performed by the This programme is supported by the Dutch coi.i technical staff of our department- The comment!, of mission for geophysics and space research of the Dis. CD. Andriesse. J. Bergman. RJ. van Duinen. Royal Academy of Sciences. S.R. Poitasch and J J. Wîjnbergen on earlier versions REFERENCES 1. Armstrong, K.R., Harper. D.A. & Low, FJ.. As- Astrophys. J. (Lett.) 164, 123 (1971a). trophys. J. (Lett.) 17& L89 (I972K 7. Hoffmann, W.F.. Frederick. CL & Emery, RJ.. :.Aumann, H.R. Gillespie. CM. & Low. FJ.. Astmphys. J. fXcrt/170. L89 097Ib). Astrophys. / (Lett. )l 57, L67 ( 1969). 8. Otthof, H. &vanDuinen. RJ.. Astron. & Astro- 3. Aurnann, H.H. & Low. FJ.. Astrophys J, (Lett. I pitys. 29.3)5(1973). IS9. LI 59 < 1970). 9. Oltfiof. H.. Aaron. & Astrophys,. in press. 4. Harper. D.A. & Low. FJ.. Astmphys, J. {Lett.} 10. Wrjnbergrn. JJ.. Moolenaar. W.H. & de Groot, G.. I82,L89(I973). Proc.5tii ESLAB/ESRJN Symp. on Infrared 5. Hoffmann. W.F- & Frederick. D.I.. Astmphys. J. Detection Techniques for Space Research (Eds. (Lett-J 15S.L9(1969(. V. Manno & J. Ring). Reidel, 1972. 6 Hoffmann. W.F.. Frederick. C.L- A Emery. RJ.. DISCUSSION R.E. JENNINGS: The brightness temperature of the central frequencies of the wavelength bands that you deduce with a large beam for Sgr A will used, it turns out that l^{:)tfi*'. What this means is surely be difficult to interpret as it contains very not clear to me yet. It is. however, interesting to see different emitting regions' that when I apply the same procedure to the measure ments of M17, this gives approximately the same H. OLTHOF: This will certainly be difficult. relation. When I plot the brighbiec temperatures as a function INFRARED RADIATION MODEL FOR THE GALACTIC CENTRE CD. Andriesse Kapteyn Astronomical Institute, Groningen, The Netherlands ABSTRACT A model is discussed which details the general a dense core with particle temperatures probably •-> view that ihe infrared radiation from the Galactic excess of 1000 ft and a halo where the temperature is Centre region originates from interstellar dust heated below 100 K and falls off rather slowly with the dis by stellar radiation. lis ingredients are the stellar mass tance. Looking in the direction of the centre, the model for the Galactic Centre devised by Sanders & spectrum peaks at about 50/im because of the halo Lowingcr, and Spinrad's model for the stellar popula- contribution in front of the core. The halo also causes lion in the nucleus of M31. Furthermore, a simple the absorption of the 9.7 pm resonance in the par theoretical oscillator model is used for the infrared ticles. The depth of the 9.7 ym band does not change radiative properties of dust particles. Some qualitative much for various directions through the Galactic remarks arc made regarding the treat-nent and its Centre region. Compared to the solar neighbourhood, approximations. the dust-particle mass is relatively small. We expect Though the study is not yel complet':, the follow the size and composition of the panicles to change ing preliminary conclusions are possible. There will be through the region. I. INTRODUCTION This is a preliminary report on calculations of radiation and become thermal radiators in the infra radiative processes in the dust associated with the red. A strong argument in support of a thermal model Galactic Centre. A more complete description will be is, that the observed infrared luminosity is compar published later*. able with the integral stellar luminosity as present in In his review of nuclei of galaxies, Burbidge the nucleus of M31. That dust particles rather than 11970J suggests that the infrared radiation from the ions and molecules emit most of the infrared can be Galactic Centre is caused by nonthermal electron inferred from the rather smooth spectral distribution processes in a number of small sources with strong of this radiation and the presence of a broad absorp magnetic fields. Pottasch [1971] has considered the tion band in the near-infrared. thermal radiation by forbidden transitions in inter Without intending to review the observational stellar ions as a possible cause. But nowadays many facts, we will recall from Borgman's paper [1973a] a astronomers think that this radiation originates from number of characteristic features which have to be interstellar dust particles, which are heated by stellar accounted for by any infrared radiation model for the Galactic Centre. • Amines», CD., van Gorkum, J.H., Ollhof, H. &. de Vries. (a) Spatial aspects J., to be submitted to Astronomy and Astrophysics. In the far infrared (50-350pm). the radiation 240 ça ANntufcsst: comes from a very extended region elongated along graduai decrease of brightness temperature is ob ihe galactic plane ©vet a few degrees, whereas in the served with wavelength lOlthof, 1974). near infrared (10- 20 jim) most radiation comes from From this much simplified description, it be a small, almost point-like region (a few seconds of comes clear that we have to do with a region where arc}. The former region (die haloj includes not only the temperature and density of the dust particles vary the latter source (the core), but also a number of considerably. Greenstein [1970| «cognised that the other sources. Close to the near-infrared core, small- relevant astrophyskaS theory had already been scale structure is visible, which tends to become more studied around 1930. If there is spherical symmetry pronounced for shorter wavelengths. Somewhat arti and the energy source is mainly in the centre, the ficially, an annular region may be defined which in result is "that when you look at the centre you see a cludes the immediate surroundings of the core with very hot star, while at the limb you see a very cool spectral properties intermediatebetweenthoseofcoie thing; the flux is not describable by a unique temper and halo. We want to disregard the additional sources ature*. The difference between Gteenstein's very hot in annulus and halo, whose presence may testify of star and tiic near-infrared source in the Galactic H It regions near the centre and red foreground ob Centre is quantitative rather than qualitative, so that jects. the basic theory needs only small extensions. The aim of our study is to detail a thermal dust lb} Spectral aspens model, so that predictions can be made of the spatial The rise of the halo spectrum from the radio con and spectral distribution of the infrared emission by tinuum to its maximum is steep and probably sleeper the Galactic Centre. These predictions will depend on than given by Jeans* law. Maximum emission occurs a number of parameters in the model, so that a com somewhere between 20 and 100 pm. The gradual parison with the observations allows us to fix some of reduction in emission towards the near infrared is these parameters. As ingredients we use a general slower than given by a single exponential law and mass distribution based on the stellar mass model of contains a remarkable depression of about 2 mag. Sanders & Lowinger [ 1972], together with Spinrad's around 9.7 ;im. This 'band' is present at the core posi model [1966] for the stellar population of the nu tion and in the surrounding structure, with almost cleus of M3l. To describe the dust particles, we use a equal strength. In the near infrared there is a large simple oscillator model for the infrared radiative difference between colour temperatures and bright properties. Although the study has not yet been com ness lemperatures, the latter being almost an order of pleted, a few qualitative remarks can be made here magnitude smaller. At least for the far-intrared halo, a about our fitment and results. 2. HEATING OF THE DUST Towards the Galactic Centre, the matter, both in with Hs(0) = 5.2 x 10* MQ/PC* and Rc = 0.3 pc. The stars and interstellar, tends to become denser. This is numerical data follow from a best fit to the mass because the galactic gravitational Held has a central model by Sanders& Lowinger [1972],the total mass singularity. Kinetic energy probably prevents the within R* being given by matter from coalescing into a black-hole singularity in the very centre, where one expects the density distri 4s n^O) R* (R* - Rc arc tan R'/R^ bution to be flat-topped. From observations by Becklin & Neugebauer {1968] at 2.2 and 3.5 Jim. We adopt spherical symmetry, though the actual which show pan of the direct stellar radiation in the distribution is ellipsoidal centre, it can be inferred that the stellar density falls The next question is how this stellar mass ladi- 1 off with IT '" over a considerable distance (60 pc). ates. Borgman |1973a| argued that for a mass- For distances in excess of 1 kpc, one can expect an luminosity ratio M/L of 3, there is no problem in 3 ÏC dependence. We adopt a stellar detaiîy distribu accounting for the observed total infrared emission. tion n^R). However, M/L is probably closer to IS [Ulrich, 1973] as a consequence of the relatively rich popula tion of low-luminosity stars. We adopt Spinrad's [1966] distribution for spectral types in the nucleus of M3Î, with M/L= 16.7. which is also used by CO. ANIlHII'&St and Tj an R = ?0U pc) = 70 K. It follows thai only tage thai the causality relations of Kramers and for distances in excess of snme 100 pc from the (in Krnnig aie salisfied automatically. In their iccciil lactic Centre is I hi strictly applicable. Foi icasons of itealment of intcistellar emission Caroft el a!. simplicity, we nevertheless have applied (M in ilir | l*»7Jl|. for example, use these relations to derive following analysis, but a more realistic calculation evidence against silicate particles. Moreover, 171 at (he will be piesenied latei. For this we use the theore same lime satisfies the observational evidence fm the tical [Seitz. 11401 prediction that strength of the ansorplton band at *).7jjm |Carofl et al.. Il>7_ï] and its width, regardless of the chemical nature of the bond resonance. With (7) we cannot analytically evaluate (4). s:i 2x t0 c ni <»>,', r" )" + ft- that the temperature field replacing!, h)has to lie com-. pt- ci. It may be cleai that (7) leads to highei tem pi .mites, especially in and near the centre, as the where n0 is ihe atomic density in a pain, ni an aver age atomic mass (about 1G proton masses), "o the cnmsion possibilities at relatively high frequencies are mosi important lattice frequency (we take oi esiimated with (Jli'l = Mi'/^)'. A rough calcu -' \ 10l * Hz in Hidei lo amount tor Ihe ib served ab lai 'n indicates that oui mode) give* Tj > 1000 K in sorption feature centred a' ^.~ tim\ and 1 the dam the cenIn-, so .liai the problem of possible evapora ping of this mode <•> * 5 \ 10l : H/i. tion of ihe giains arise*. II one believes in grains con sivting ol a silicate core and an 'ice' mantle, one car Why this theoretical formula and noi expéri expeel thai the mantles will disappear or du not grow mental data on QO'Jfoi silicates or graphite'' First, in at all m the central region. One might even undei- principle we can as well «eat the problem with nu sund llic appâtent visual absence of dust in the core merical data obtained for such substances, hut the of M3I in teims of a strong thermal disintegration problem is that hardly a consensus cxisis on the |Johnson. 1174]. In any case, one can hardly avoid chemical composition of the interstellar grains. Che the conclusion that the sue and composition of dust mically pure suhsisnces cannot be expected, so thai a particles will not be the same throughout the Galactic- degtee of arbitrariness enters as to which mixtures Centre region. should he studied further. Secondly, a more sche matic theoretical absorption spectrum has the advan 4. RADIATIVE TRANSPORT We are now in a position to calculate the trans sume an average extinction of 2 mag/kpe. This leads port of infrared radiation, emitted by individual roughly to the same mass ratio of stars and dust for grains, along a line through the Galactic Centre. This ihe nearby spiral arms. However, it is doubtful wheth is not a trivial calculation, as observations make it er this is realistic tor a region which in su many as clear that the optical depth of the Galactic Centre pects deviates from the solar vicinity. From our region in the infrared varies from large to small. We preliminary results, we derive that njlOl is lower. Wc have, in general, fir the intensity I recall that Johnsun [1474] noted (he apparcn' ab sence of dust in the cote of M31. -«,1 + KB^T,,! Both KS and B5 depend on the position in the Galactic Centre region, which makes the solution rather complicated. Analytic reduction for a line where ds is a line element, the absorption coefficient precisely through ihe centre leads to the solution 3 R * s = nda7 QM- nd £°" in analogy with ( ! ), and Q(i») 2lic D c is given by (7|. The spatial behaviour of the source term B^v, Td) follows from (6). For nd(0). we initial ly adoj»i the value 3 m~3, which is the density to be iw expected when the mass ratio of stars and dust is I / exp 1 (9) 1000. To justify this number, we «call that Purcell RJD-r) (1969] quite generally derived a lower mass in dust : exp | n.i{0)aR(.Q(i')arctan ] particles in the solar vicinity, for which one can as R* + Dr )H kAtJUriON Wipl I IOK1FII <;.\LACTH H NTKl 243 Figure J. Contribution l(v) in fv ' //: ' w-"1 to (he spectrum ftv lines • Vg.ht through and at V fri/m the Oalacttt Centre. The unhmken curves are based nn a first guess iif the mndei parameters, the dashed curves im an ad-hoc assumption of the dust temperature m the cent*" tiee text). These preliminary results lia-- • «« other pretention than tu find the • -nsity and temperature of dust particles v -ugh the (ialactic Centre region. ence between c»i»ur and brightness temperatures Isee introduction) points to a system where Ihe optical depth cannot be excessively high. When the hot core is allowed to be rather thin optically at 10 pm, we get the resonance in emission from there, so that the depth of the band will be reduced. Very recent rest computations with nj(0)s 0.3 m"3 confirm this- (Actually the outer dust will be heated by the absorp tion at 9.7 pm m addition to the absorption of visual and ultraviolet starlight. We guess and hope to prove Here D is the dislance In the Galactic Centre of thai the infra^d heating is negligible compared to the R.I kpc (Plaut. 1973|. A sliglnly more complicated direct heating.) solution is obtained for lines of sight beside the centre. Inserting TJ(I) from (ft) and Q(t>) from (7). From Figure 1 it is evident that the near-infrared we find numerically the h» sketched m Figure 1 emission is relatively too weak. This has to be as (unbroken lines!. cribed to the too-low core temperature given by (6). Despite large discrepancies in the actual spectrum, It remains to be seen, however, whether an improve some things are aJready striking. We find a maximum ment in the temperature field suffices to account for emission at about 50 um and the resonance at 9.7 pm the observed spectrum. To illustrate possible changes, in absorption, both in agreement with the obser we made a test computation based on (6), but with vations. If nnc could apply Wien's displacement law, an arbitrarily chosen central dust temperature of the apparent source temperature would be only 60 K. 1000 K (see Fig. 1. dashed Unes). Such a change We have seen that this is an illusion, but it indicates works in the right direction, of course. For lines pas that the tenuous cool halo in front of the core contri sing beside the Galactic Centre, we obtain the fol butes significantly to the entire emission. Note that lowing qualitative picture. Unfortunately, the effects the emission towards the far infrared decreases quite are very much masked in Figure I by the excessive sharply, approaching there the v* power law dis optical thickness. Going out from the centre, the cussed by Andricsse & Olthof [I973|. A sharp near-infrared part of the spectrum decreases more decrease is required to account Tor the low flux from rapidly than around 50 urn. which explains why the the Galactic Centre at 350 um [Gezari et al., 1973|. extent of the Galactic Centre source seems to be wavelength dependent. The lower the near-infrared In our calculation, the particle density in the flux, the less selective extinction is possible at centre is assumed to be so high that we arrive at an 9.7 pm- The observed "invariance of Borgman's optically thick core.. For this reason the 9.7 ftn\ reso ( 1973b] parameter a for various positions in the nance, which will not app-'"r in emission for the core, Galactic Centre area is thus understood as a trivial is seen in strong absorption through the coo! halo. consequence A our model. (We have omitted the The calculated absorption exceeds the observed near-infrarea sources which surround the galactic strength of the band by many orders of magnitude. core. A similar argument makes it clear that for all We take this as evidence that we have overestimated these sources o should be about the same.) the particle density. Indirect evidence from the differ- 244 CIV ANDKIi-'SSI S. PRELIMINARY CONCLUSIONS Though [he analysis of our model is rot yet com particle temperatures probably :n excess of 1000 K, plete, some questions can be answered. Does the view and a cool halo, where the temper» tu re falls off that the infrared emission from the Galactic Centre rather slowly so that the emission comes from - very- regiiw is thermal radiation by dust panicles heated by extended region. Even foi the very centre, the spec the local stellar radiation field, stand a detailed con trum peaks at about 50jim, mainly because of the frontation with the most recent observations'1 The contribution of the halo in front of the core- The answer is yes, because the ingredients of out model latter also causes the observed absorption band at are straightforward and nothing exceptional has to be 9.7 ;im, the relative depth of which does not change assumed to arrive at the observed spatial and spectral much if one takes another line of sight through the distribution of the radiation, We adopt a distribu central area. tion nf uii;: pain-lés following that of the stars and a Are such conclusions very dependent on our similar mass ratio of d-jst and stars as is known to model and its approximations? Mow serious is the exist in the solar neighbourhood. The latter assump propagation of certain assumptions? We have yet to tion probably has to be changed Furthermore, a con study these questions, giving special attention to con servative estimate is made for the stellar radiation sistency. When, for example, the grain composition is field heating ihe dust panicles, based on Spinrad's variable, it will certainly affect the calculation of tem analysis of the stellar population in the nucleus of peratures throughout llie Galactic Centre region. We M3I. We haw finally applied a rather unbiased theo hope to gD into these-matters in our final paper. How retical model for the emission propenies of dust par ever, from ihe qualitative results so far. we conclude ticles in the infrared. that the main features of the model described here All this suffices to predict a hot dense core, with are realistic. REFERENCES 1. Andriesse, CD. & Olthof. H-. Astron. A Astro- 10. Greenstein, J.L, Dark Nebulae, Globules and phys. 27, 31° (1973). Protwsiars (fid. B.T. Lynds, Tucson, p. 128, 2. Becklin, E.E. & Neugebauer. C, Astrophys J. 1070). 151,145(1965). 11. Johnson. H.M., Proc. IAU Symposium 52, 215 3. Borgman. J.. Paper at 1AU Symposium 60, (1973). Maroochydore, 1973a. 12. Olthof. H., Paper at ESLAB Symposium 8, Fras- 4. Botgnwn. )., Astron. A Astrophys. 29. 443 cali, 1974. (1973b). 13. Raul. L. Astron. A Astrophys. 26, 317 (1973). 5. Burbidge, G.R., Ann, Rev. Astron. A Astrophys. 14-Poitasch, S.R., Astron. A Asirophys. H, 152 8.369(1970). (1971). 6. CarofT, LJ„ Petrosian, V, Salpeier. E.E.. 15. PurceJl. E.M., Astrophys. J. 158,433 (1969). Wagoner. R.V. & Werner. W., Mon. Not. RAS 16. Sanders, R.H. 4 Lowinger, T., Astron. J. TJ, 292 1*4.295(1973). (1972). 7. Ekers, R.D., Go». W.M., Schwartz, VJ-, Dowries, 17. Seitz, F., The Modern Theory of Solids, McGraw- D. & Rogjtad, D„ in preparation. Hill,pp.631,634, 1940. 8. Gezari, D.Y., Joyce, R.R. & Simon, M.. Astro- IS.Spinrad, H„ Pubt Asffor. Soc. Pacific 78, 367 phys-J. 179, L67 (1973). (1966). 9-Greenberg. 3M„ Astron. A Astrophys. 12, 240 19. Ulrich, MR. Paper al 1AU Symposium 58, Can (1971). berra, 1973. IK RADIATION MODKL FOR THF GALACTIC O-.NTRt 245 DISCUSSION li. BUSSOLETTI: The physical meaning of the C. ANDRlESSfc In our model the temperature ii temperalure distribution is not clear to me in the determined by the siellar radiation only. V.'e hope to sense that you expect hot and cold dust practically prove that this is the main lerm. However, the heating everywhere with a higher concentration in ihe centre. of dust in the halo by absorbing around lOym cer tainly plays a rule, li will be difficult to get a good f". ANDKlHSSfc: Our calculations give a tempera- estimate of this heating by infrared from the core. line field which peaks sharply in the centre and falls off slowly I pc or further from the cenire. In a line of B- BALICK: In the radio continuum synthesis sight towards the centre, you meet both (he cold dust observations made by Sanders and myself, we find in front nf the core and the warm dust within the bright fine structure of size ~- 0.5 pc whose spectrum core. is increasing with frequency and whose brightness temperalure is a few thousand degrees. We interpret V. PETROSIAN: AS you are doing ihe radiative Ihc structure as H II regions: your model predicts that transfer of a rcsonjnl line throughout the Galaxy, I lIns structure is hot dust. Is it possible we have mis think it is unrealistic to ignore the Galaxy's diffe interpreted our results" rential rotation. This could be one reason why you gel such a large dip in your resonant absorption. C. ANDRIESSE: I would not say so. Any new observation showing structure below one arcsecond. C. ANDRIESSB: The line 1 am considering is very which corresponds to l/TO parsec, does harm our broad: the damping is enormous. It is not an atomic model. We base our study on a picture of the galactic line, but a line of a regular lattice, so thai the broad core as a coherent region about 12 parsec in dia ening is much larger than you would expect from the meter. In this region the dust will be hoi. It may well differential rotation. be thai the stellar radiation field, responsible for this heating, also efficiently excites the electron plasma. So we can understand a coincidence of the hot dust P. CLEGG: Is the temperalure distribution in source and a compact H II region with high excitation your model determined solely by the stellar radiation, temperature, about 1/2 parsec in diameter. But any or does the re-radialed infrared play an important smaller structure would disturb this picture so that role? we should start thinking about another theory. RECENT RADIO OBSERVATIONS OF THE GALACTIC CENTRE D Dowries Max-Planck-Institut fiir Radioastronomie, Bonn. Germany ABSTRACT Tins paper reviews recent radio continuum obser ponenl of diameter 45" which surrounds the calactic vations of the (ialactic Centre Region made at Cam nucleiis. as defined by the maximum surface bright bridge, Westerhoik and Bonn, The new maps show ness al 2.2 (im, and a nonthermal component ut dia considerable Tin: structure in the sources G 1.1 -0.1. meter 150" which may he a supernova remnant. Five GO.9+0.1. G0.7- 0.0 (Sgr B2). C0.5 0.0. G0.2 0.1 sources smaller :han 10" are found within a 5 x 5' and G359.4-O.I. Tlie observations of Sg: A confirm field ce-.ired on Sgr A. A radio source of angular dia the general division into two sources - a thermal com- meter <0.1 " may be the actual nucleus of the Galaxy. This paper deals mainly with radio continuum ob Ihe reader is referred to recent discussions by Scoville servations of the Galactic Centre Region, and with el al. [1974], Sanders & Wrixon [1974| and refe the relation of the radio sources to the infrared rences therein. Nor will I deal with the extensive ob sources. servations of radio recombination lines toward the 1 will not attempt to review the observations of nuclear region, which have been reviewed by Mezger molecule sources in the Galactic Centre, for which ct al. [ 1974] and by Gordon 11974[. 1. RADIO CONTINUUM OBSERVATIONS OF SOURCES WITHIN 0.1° < IKl< 1.2° OF THE CENTRE I review the radio progress on these sources shown in Figure I. The sources comprise: because they do appear lo be in the nuclear disc, on (i) GI.I5-O.07. an extended H II region of angular the basis of the velocities of their hydrogen recombi diameter 5.5' x 6.8'. The H II region emits a nation lines or the velocities of HI, OH and H3CO hydrogen 109a recombination line at -21.7 kn/s absorption lines seen in their directions. Consequent (Reifenstein et ai., 1970), and an ammonia cloud ly, I think all of these sources will be of increasing has also been delected in the direction of tiie interest as new infrared maps with high angular reso source [Cheung et al., 1969; Knowles & Cheung, lution become available. 1971J. (ri) GI.13-0.11, a compact H It region of angular dia meter (12" x <30") which has been detected 1.1 THE COMPLEX AT8=1.J° interfcrometrically at 5 GHz (Ekere &. Lynden- Bell, Ï97IJ, and which shows up as a strong peak A map of this source region made al 10.7 GHz is on the 10.7 GHz map (Fig. I). This source is Figun l. Contour map of the source complrx near galactic longitude 1.1°. nude at lti.?GH: win the tlffehbeig HlOmtelv- snipe. Vic fialf-ponvr bcarxwidlh is 77*. Ttie cross marks the ptisttion at which amntniua has been observed /Cheung ct ai. /Vft«- Knowles & Oteung. !»?]/. tine ii >njour unit = |).?S5 ATtf apparently optically thick at centimetre »jve- lengths. like K3-50 and W3(01h. and one might expect it to be delected in the infrared, when the area is mapped ai !0 - 20/jitt with — 5" reso lution. (mIG1.054.1. a nonthermal region of emission of diameter ~fe' x 6" which has a radio spectral in dex of -0.6. and which t probably a supernova remnant. This source is relatively weak on radio continuum maps at frequencies >5 GHz. hut shows up strongly on the Molonglo map at 408 MHz (Utile. 19741 (.lv>Cl.l-0.1 more precipe co-ordinates not available. a remarkly strong source of flux density 150 f.u. BEAM O at 25b MHz which was discovered during lunar occultation observations jTaylor. 196S1. The radio spectra of these four source* arc shown in Figure 2. Il may he that because of the difficulty of separating source contours from the strong galactic ridge radiation, the values quoted for G1.05-0.1 at 408 MHz are underestimates, and that this source and the low-frequency source seen by Taylor are one and the same. An alternative possibility is that a strong pulsar with a steep spectral index exists in the direc tion of Gl.05-0.1. It would be of interest to search this region with fast-sampling receivers. 1.2G0.9+O.1 This source is probably located in the Galactic Centre, on the basis of the H2CO absorption in this direction, but as yet il has not been detected in the infrared. No recombination lines have been found in this direction (Reifenstein et al. !970;Mezger et al. 1974], which suggests that the source is nonthermal. The spectrum of G0.9+O.1, however, is remarkably flat ( I BEAM Contour map <>} 00 '1*0. I made wo It the Westerbork télescope at > (,flz 'Ii'.lf ({oss. private communication i. pw reso 4^30* lution fialf-widths are 5. J" x .W/ source inio compact components. In this respect and The cure of the infrared cloud, seen al 35Ujjm . wiih its flat spectrum, the source is similar to the [Rieke et al., I97.1J is slightly lo ihe north ot die supernova remnant 3C5K. molecular core, although its finite diameter encom passes the region of the compact radio sources (Fig. 6). The fact that the compact iadio H II regions 1.3 Sgr B2 AND G0.5+0.0 in Sgr B2 are not prominent at wavelengths 10 - The new map of the Sgr B2 region, made with the 20 pm. may indicate heavy extinction in the infrared. 100 m telescope al 10.6 GHz with a beam ot" 77" is Such extinction would be consistent with the high shown in Figure 5 [Downes & Gardner, I974J. The density inferred for the Sgr B2 molecular cloud and map shows that both of the H II regions Sgr B2 with the low intensity of radio recombination lines of (GO.7-0.1) and GO.5+0.0 are resolved into a number helium in Ser B2 (see the discussions by Jura A of components of angular size 1-5'. In general these Wright, 1974,andChurchweUetal.. 19J4]. components of intermediate angular size do not coin A remaining controversy in Sgr B2 is the nature cide with ihe line structure components smaller than of the source detected at 3 mm by Hobbs et al. 10". which have been found with interferometers 11971 J. The position of ihe source given by Hobbs et [fckcrs & Lynden-Bell. 1971: Marlin & Downes. al. does not agree with any of the compact sources 1972; Balick & Sanders. 1974: Fclli et al.. I°74,. found at 2.7. 5.0 or 8.0 GHz (Martin & Downes. The relation of the Sgr B2 continuum at 1972: Balick & Sanders. 1974]. Fclli et al. [I974] 10.7 GHz to the infrared distribution and to the report a compact component near this position at molecular line sources at radio frequencies is illustra 10.7 GHz, although it seems odd that such a compo ted in Figure 6. The radio continuum peak at nent would not have been detected by Balick & i0.7GHz. and the cluster of compact radio sources Sanders [1^74] at 8.0GHz. Kapitzky & Dent [1974] seen with the Cambridge One-Mile Telescope at seem to doubt the existence of this compotier' (i.e. as 5 GHz. are located near the position of the mascr shown by a rise in the flux of Sgr B2 at 3 mm), while sources seen in OH and HjO and near the core of the Simon [1973] shows that the 3 mm source could be molecular cloud. Densities of molecular hydrogen in the longer wavelength radiation from the dust cloud excess of 107 cm"3 have been inferred for the core of which is detected in Sgr B2 at 350 pm. the molecular cloud from the detection of short-lived My personal belief is that such a component does transitions of non-metastable ammonia JZuckcrman exist in Sgr B2 and that efforts should be made to et al.. I97I) excited OH |Gardneret al., 1971].and confirm its position and size at wavelengths of I and methyl cyanide [Solomon et al., I971). 3 mm. I) no v. NI s 17" u" RIGHT ASCENSION (1950) Figure 5. Contour map of GO.7-0.0 (Sgr B2) and GO.S-0.0 nude by Dowries & Gardner 11974} with the 100 m telescope at 10.7 GHz. Contour unit = 0. ! 88 ? Ta. RI CI NI KAIllO DUS! KVATIONS (Il - (ÏAI Al'IK f I SJHî ,t L MQwin'«i"»'-«o-f'"wo' HL épatas H.CO v. 1 - • 75-M H« Ï.-1, --• -60 OH 'nl;. J.I., «Mn AFCW81N4TI0N-LIW YELOCif» Ikm % 'i « KCt.NâTOW îf M- IB' OECLittAtiONt 195001 Figure 6. Comparison of the extent in declination of radio continuum radiation in Sgr B2 with the Imif-widths of infrared radiation {Rieke et aL 1973} and molecular clouds. Tlie variation ofH92a recombination-line velocity with declination (lowest scale) is from Chaisson (1973J. Thisfizure from Dawnes & Gardner (19741, who give the references to the molecule data. Outward-pointing arrows give lower limits to cloud sizes, inward-pointing ones give upper limits. Otherwise, the bars give the measured halfwidths of molecular clouds. l.4(;35').4-0.1 The 10.7 GHz map cf this source is shown in Figure 7 The source is locate d on a ridge of apparent- ly ilirrmal emission aligned along Ihc galactic plane. Although ladin recombination tines have been delec ted IIKIII the ridge |MeKgcr et al., 14741 no line has been found in ihe source, and comparison of it-, flux density at 10.7 GH?. with that derived by Linle | )«»74f at 408 Mlfe, suggests llial it is a m>nhViiu;il source, presumably a supernova remnant, with a vpec- iralmdc\ of 0.5 +0.1. There is, however, an inflated source seen at lOOym (Hoffmann et al.. 11711 m the direction ul' G.*5g4 0.1. Tire situation is slightly unusual m thai most ut the 10Q;irn sources in the survey h y Hoff mann et al. are associated with II II regions. 1.5G0.1+0.0ANDG0.: 0.0 Figure K shows the 10.7 GHz map of the region extending from Sgi A to the sources G0.1 0.0 and GO..- 0.0. There is a consider ah le amount of new detail in this map. the main results being as follows, (i) The source formerly called GO.t+0.0 is resolved into at least four distinct peaks and a narrow arc- shaped ridge rising above the galactic plane. Une of these peaks lies near a compact source seen 30" 1 7" 4 TOO* with die NRAO interferometer by Balick & RIGHT P5CENSI0NI19S01 Sanders |ll»74|. (ii) The source formerly called G0.2-0.0 is shown lo Contour maps ofG35V.4-0.1 made with be an extremely narrow ridge with two main the 100m telescope at 10.7GHz. Con- peaks, which lies almost perpendicular lo the lour unit = 0.285 k T„. galactic plane. This ridge is a quite remarkable feature which seems lo run for a considerably larger distance than the bnu.idaries of Figutc 8, and wliich is best seen on coni-j..- maps at lower frequencies. The uppermost ol ihe two compo ^: nents, GD.18-0.05. has a strong H 109a recombi •l&'LV nation line [Reifenstein el al.. 1970J. The lower Éf7^s> component G0.f6-0.i6 apparently has no line [Pauls «1 aL, 1974] and may be nonthermal. Further evidence along these lines is provided by •' ^*vWÊÊfi$3nm the continuum maps. GO-18-0.05 is the stranger S-M'W source at 10.7 GHz, while GO. 16-0.16 is the more ''l'^^^Ww^Ê •• ' prominent source at 408 MHz [Utile, 1974]. (iii)The general background underlying these sources D-28»W and Sgr A constitutes the uppermost contours of what has formerly been called 'the extended ther- -M"» 0 WSÊÈ- Contour map ofSgrA and the G0.2-0.0 ^ilïpyj region made with the J 00 m telescope at 10,7 GHz. Contour unit = 0.285 K T„. RI TINT RADIO OBSI-RVATIUNSOI- CM.M'IIC a NTKI 253 mal source". The continuum emission from Ihis the 42 m telescope at NRAO The (.(inclusion-, ul I'omponcnt ex lends a considerable distance be this study arc that yond the boundaries of Figure K and can besi be (a) the strongest line "mission comes from the seen in Ihc contour maps at lnwcr frequencies narrow arc-shaped region al GO. 1+0.0: |c.g. Cooper & Price, J 964; YVhjlcoak & Gardner. (b) negative radial velocities of 50 km S pre ll>7.1|. It is clear from Figure S that there is con dominate in the ionised gas at GO.OO+0 00. siderable structure in this extended distribution, near Sgr A, in contrast to the positive veloci and thai it is in tact composed of a large number ties of +20 lo +()(j km/i wen in the molecular of discrete sources uf emission measure — ]IJ4 clouds in the direction of Sgr A- enf * pc. (c) in the ionised gas. negative velocities jppeaf. livjThc extended thermal area shown in Figure 8 has on the average, below the ialnclic equator. been extensively mapped by Pauls ct 3I. [1974| positive velocities above the equator. in the H85a recombination line 3t 10.5 GHz with i. RADIO CONTINUUM OBSERVATIONS OF Sgr A 2.1 NEW MAPS The 10.7 GHz map shown in Figure 8. made with a beam width of 77", shows only that the contours of Sgr A have a steep slope on the weslern side of the source and a gentler slope on the eastern side. Further resolution of the source requires interferumctric ob servations or lunar occultation observations. Radk results in the past few years have con firmed the general picture of two main components within the 3' source which was formerly called Sgr A. These two main components are shown in two-dimen- sional maps at 1.4 and 1.6 GHz (Sandqvist, 1974; 1 i Wr^Wà Christiansen, private communication f, 4.8 GHz [Whiteoak et al., 1974] and 5.0 GHz [Ekers ct al.. 1974]. Figure 9 shows the map from Ekers et a). The novel feature of this map is that it combines data from two different telescopes - Westerbork and Owens Valley - to obtain complete coverage of the (u,y) plane. The result of this procedure is a synthe- sised beam of 6" x 33", with a relatively low sidelobe »»' ASCENSION I195CPi level. The map in Figure 9 shows: (j) the broad, non Figure 9. Contour mep of Sgr A. made ai 5 Gtii thermal eastern component, which has an angular size with the Westerbork and Owens Valley of I SO", and which contains most of the flux density telescopes /Ekers et ai, 1974}. Oie con of Sgr A as seen with instruments of lower resolution; tour unit= 5millijlux units per Leam and (ii) the bright, thermal, western component of area, ffàlf-power beamwidtlis are 6.1" x overall half-width 45". Because these components 33"{RAxdec.). were resolved several years ago with radio data which had maximum discrimination in the east-west direc tion, they were referred to as 'Sgr A East' and 'Sgr A components is shown in Figure 10 [Jones, 1973]. West*. Now that two-dimensional maps of these com This plot is also given by Dulk & Slee [1974], and ponents are being made, it seems better to return to the interpretation of the continuum spectra of Sgr A the less ambiguous designation of these sources by is similar to that deduced by Lipovka [1971], al their galactic co-ordinates. though with somewhat different component para The radio continuum spectra of these two major meters. lï LMÏWNfcS trum, and the source probably Iwcnmrs optitalh (hick tor Irequencics less than I GH? S* a TjTt «lSu»Ct> Tire radio continuum map al 5 GHr m Figure ') FlW COWÏCT£S «* suggests thai G 0.06 (1.05 has ai least three subcom CCWSUUT SCLD AIME ponents. Tins line-scale structure has been reported S«r & East OCMvtD previously by Fkcrs & Lynden-Bcll (1'171), Downe* & Martin I!°7l| and Balick & Sanders |l«74| The new Cambridge and Westeibork results show further details of this siiucture Fipure 11 shows the radio contours or G 0.06- 0.05 from the Cambridge data al 5 CM?. alter Hie strongest sidck>hes were removed in an île- ratii-c procedure developed hy S. Gull and A.H.M. Matlin. The extent of the lowest contours is exaggerated in the north-south direction because of the Ilm.ied coverage in ihc(u.v) plane. Superimposed Fiptrc 10. ftaJio continuum spectra of the two main on the radio contours are the positions of the five ciimpuncnti of Sgr A (from Jones. sources seen al 10pm (Rieke & Low. 197.1. Borg- lv?3j. man. 1974|. Also plotted are the position of the poim source at 2J*iin |Becklin &. Neugebaucr. l^ftSJ and the pmtlton of maximum suiface bright 2.2 THE NONTHERMAL SOURCE. G 0.04 0.06 ness at 2.2 pin. (Sgr A EAST) The nonthermal source C-0.04-O.06 has a spec tral index of about -0.5 and a flux density of about 90 f.u. at 5 CHz. The source has recently been map ped with the Culgoora telescope at a frequency of 160MHz by Dulk & Slee 11974). They measure a brightness temperature at the source peak of 63 000 K. and with a correction foi their beam - ize of 1.9'. the true brightness Ic.iperature of the s( urce at 160 MHz is probably > 10s K. In spite of the fact that this source is nonthermal, recent interferometer measurements at Cambridge at 17 and 5.0 CHz [Martin & Downes. 1974| and at Westerboik at 1.4 and 5.0 CHz |G. Miley. private communication; Ekers et al., 1974] show no polari sation to a level of about 10%. Synthesis maps of formaldehyde absorption at 4.8 GHz [Whileoalc et a]., 19741 suggest that the nonthermal source is lo cated behind the actual centre of the Galaxy (see the •3GW ASCENSION (ISSÛO! discussion by Oort (1974) of a possible model of the source location). figure J1. Map of the western component of Sgr A. G-O.06-0.05, made at S GHz with the 2.3 THE THERMAL SOURCE COMPLEX. Cambridge One-Mile Telescope (Martin & Downes. 19741. Qrclespositions ! -5are G-O.06-0.05 (Sgr A West) the peaks of the 10 pm sources listed by Rieke & low [1973]. Vie triangle marks The thermal source G-O.06-0.05 is coincident the position of the 22 pm point source with the maximum of the 2.2 pm surface brightness I Becklin & Neugebaucr. 1968}. Vie cross (E. Becklin, private communication], which suggests marks the position of the radio point that it is actually located at the centre of mass of the source (Balick & Brown. 1974} and the Galaxy. G-O.06-0.05 has a flux density of about maximum surface brightness at 2.2 pm. 30 f.u. on the optically thin part of its radio spec HKJNl RADIO WiSf-lRVATIONS(11-CALACTK f I NTRI 255 A number of conclusions can b** drawn from Fig 2.4 THE RADIO POINT SOURCE ure II. Tlieie is poor agreement between Ihe radio peaks it 5 Gil/ and the sources at 10/jm. In parti The fringe amplitudes seen with the Cambridge cular. Rickc & Low's source 1 and the strongest radio and Weslerbork lelescopes have a constant level of peak are separated h y about 3" in RA and 7" in dec. about 0.5 f.u. at aerial spacing* between 10 000 and There is no radio component coincident wilh the 25 000 wavebngths. This result indicated an unre 2-2 fim source 3. ACKNOWLEDGEMENTS The author wishes to thank B. Balick. E. Becklin. for assistance. 3nd for providing data prior to publi- R. Brown, R.D. Ekers, F.F. Gardner, W.M. Goss. cation. . K.Y. Lo, A.H.M. Martin. P.G. Mezger. and T.A. Pauls REFERENCES 1. Allenlioff, W., Downes, D.. Goad. L. Maxwell, A. 7. Chaisson. h J., Astrophys. J. 186. 555 (1973). A Rinehart. R., Asmm. Astrophvs. Suppl. 1.319 8. Cheung, A.C.. Rank, D.M., Townes, C.H. & (1970). Welch. WJ., Nature 221.917 (1969). 2. Balick. B. & Sanders, R.H.. Astrnphys. J., in 9. Churchwell, E.B., Mezger, P.C. & Smith, L.F.. press. AstroiL Astrophys.. in press. 3. Balick, B. & Brown, R.L., Asirophys. J., in press. 10. Cooper, B.F.C. & Price. R.M.. in Thf Galaxy and 4. Becklin. E.E. & Neugebauer, C., Astrophys. J. Ihe Magellanic Clouds (Eds. FJ. Kerr and 151,145(1968). A.W. Rodgers), Canberra. Autra!. Acad. Sci., 5. Borfc.-rian, J., Proc. IAU 60. in prêts. p. 168,1964. 6. Brown, R.L ABroderick, J.J.,/lîfrop/i.yî./. 181, 11. Downes, P. & Gardner. F.F.. in preparation. 125(1973). 256 o txmMs i: JVwnes. D. * Martin. A.HM., Saturr 1M. H 2 31 MMjter. PG . Chmthweli F.. A Paiib, 1 . in Star. H»»7H and the Milky Way System DISCUSSION A. PEDLAR: Could the recombination lines near K.W. MICHEL: Can you lell from the line shape Sag A with velocities - - SO km/s be associated with of this recombination line which fives 200 km/s •JK 3 kpc arm? whether it b miaoturfaulence or whether it is pre dominantly directed? D. DOWNES: Not the ones detected by Pauls et •1. {1974) at 3 on. The ndial velocity changes too D. DOWNES: No, I think the experiment will rapidly with galactic longitude to be associated with have to be repeated at a higher frequency where wt the 3 kpc arm. can expeel a better signiMo-noise ratio. 257 OBSERVATIONS OF NEUTRAL HYDROGEN IN THE REGION 355° < l" < 10° AND -S° < b" < 5° R.J. Cohen & A. Pedlar Nuffield Radio Astronomy Ubtintories, Jodrell Bank. Cheshire. UK ABSTRACT Tim paper reports op stuGics of the 21 cm hydro- .15' HPBW) and Mark IA < I ? HPBW» radio telescopes gen line hum the central regions of the Galaxy. The ai NR/ L. Jodrell Bank, instruments used for I. THE OBSERVATIONS The Mark II survey was carried oui in September The Mark II survey covered the region 355°< l" 1971 using a 90 K receiver. The Mark IA observations < 10° and - 5 < b < 5? with latitude sequences every followed in the spnngof 1973 using a 130 K receiver. 1° in longitude. The region -3° < b < 3° was sam- The spectral analysis in both cases was achieved byy pled every \i beamwidth (W°). The rest of the region means of a 256 channel autocorrelation spectrometer was sampled at least every beamwidth (Vi°) and [Davies et al., 1970]. This was operated with aa where time allowed every Vi beamwidth. Six of the 5 MHz bandwidth, giving a velocity range of latitude sequences were re-observed at higher angular 1060 km/s and a velocity resolution of 7.3 km/s. Thes resolution using the Mark 1A (J11 = 10°, 7°, j°, 2°. spectra were separated from the receiver pass band byy 0°, 358°). A number of longitude sequences were switching 4 MHz. Integration times of order 10mini taken to investigate interesting features which ap were used and the RMS noise was typically 0.1 K. peared on the Mark II survey. The spectra from each The baselines were calibrated using a reference regioni sequence were combined to produce latitude-velocity at G 10.0 + 20.0 and are believed to be accurate tos contour maps, examples of which are shown in Fig 0.2 K. ures I and 2. 1 THE RESULTS The results of the survey can be summarised in believed (e.g. II. VII. X and XII). The present survey Figure 3. This shows the loci, in the longitude-veloci is in agreement with the recent observations of San ty plane, of all the high-velocity features detected. In ders et al. 11972J "here feature XII is uiown to ex general the survey confirms and extends the obser tend to negative longitudes. The *F feature of vations of Van der Kruil [1970], several of his fea Sanders et al. is also seen. tures being found to extend further than hitherto Six new features have been detected and are label- H.J. COmS* A. ril>l.AR led J] 10 J6 in Figure 3. All these features «cut away liom the palactic plane. ! 1 & ra.^.^4..jli~,..,v s^$SN>'i' JroV^C-p li1 " ' ' --^-"^ ^ B" 0 ^'ilV^I^'- '••. -4 i r':-\ -300 -200 -100 0 100 200 300 V,_(km/s) Figure 1 The I =358° latitude-velocity map as measured on the Mark 11 radio telescope. Contours give antenna temperature in degrees K >m^ e> T^n—M ST Figure 2. The I = 358° latitude-velocity map as measured on the Mark lA radio telescope. Contours give antenna temperature in degrees K. OBSI HVATIONS 01 NUTKAL HVDttUfiKN ,c-r 358 356* "CC 20C VELOCITY Ihr-s ) Figure X hmgitude-velocity diagram showing the high velocity features detected in the survey. The roman numeral.', follow the convention of van der Kruit ft9?0f. and the prefix J indicate features dis covered in the present survey. The small numbers indicate the mean latitude of features. A full description of all the features will be published elsewhere. 3. CONCLUSIONS The observations furnish more evidence for the inclined to the galactic plane at an angle of about 8°, expulsion of gas from the central regions of the Ga as noted by Kerr [1967], In addition, we have found laxy. The low angular momentum about the centre of two new features out of the plane (J2, J4J in the the gas out of the plane suggests that it has been KO, b>0 and IX), b<0 quadrants, whose density, emitted from, rather than fallen into, the centre. ridges point away from the centre at rather sleeper Higher expansions! velocities and lower rotational angles. Furthermore, those positive-velocity features velocities are found towards the nucleus. which lie beyond the nucleus occur at positive lati A second important point to note is the sym tude, whereas the negative velocity features lie be metry about the nucleus in the distribution of gas out neath the plane on the near side of the centre. of the plane. The ridge of maximum H t density is 1. Davies, R.D., Ponsonby, J.E.B., Pointon, L. & de 3. Kruit, P.C. van der, Astron. A Astrophys. 4. 462 Jager, G., Nature 222.933 (1969). (1970). 2. Kerr, FJ., IAU Symposium 31 (Ed. H.van 4. Sanders, R.H., Wrixon, G.T. & Penzias, A.A., Woerden).p. 239. 1969. Astron. AAstrophys. 16,322(1972). 260 ^ COHEN ft A. PEDLAR DISCUSSION M. MARW1T: Can you tell the difference between centic, we would expect them to have rotational an expansion and a rolling motion with axis in the velocities higher than the circulai velocities, for con plane of the Cauucy? servation of angular momentum. A. PEDLAR: An overall rolling motion of gas W. JAFFE: Can you determine the rotation vein- would lead to a high gradient of observed velocity city of the object which threw this miierial out'.' with latitude for the individual features, whereas we only see large velocity gradients with latitude in a few A. PEDLAR: 1 do not think there is a simple way of the fainter features, such as X, i 1 and J 2. to do this. The observed angular momentum gives you only an upper limit to the original distance of the A WHITWORTH: You quote the low angular gas from the centre. Also you do not know what the momentum of the arms as an indication thai this braking forces have been as the gas encountered mate material is expanding from the G.C. Is this a good rial moving at a different velocity. test? A. PEDLAR: If the features originated further out in theQalaxy and were collapsing in towards the INTENSE SUB-ARCSECOND STRUCTURE IN THE GALACTIC CENTRE Bruce Balick Lick Observatory Board of Studies in Astronomy and Astrophysics. University of California, Santa Cruz, USA Robert L. Brown National Radio Astronomy Observatory*. Charlottesville, USA ABSTRACT The detection uf strong radio emiision from (0 <0.1"J struciure in die inner 1 pc core of the bright (brightness température > 107 K), unresolved galactic nucleus is reported. 1. INTRODUCTION The nucleus of the Galactic Centre has been ders, arc shown in Figure 1. Based on a spectral ana studied intensively over the past few years. Riefce & lysis of their data at 2.7 and 8.1 GHz, Balick & Low 11974] have found five small-diameter sources Sanders concluded that the fine structure was prob of infrared (IR) emission in an extended background ably quite similar to the structure seen in many H II of angular size — 20". Radio synthesis observations regions, and therefore resulted from thermal radiation 4 3 have been made of this same region (called *Sgr A from a dense (Ne 3 10 cm" ) gas at a temperature of West' by radio astronomers) with spatial resolutions 10* K. We therefore observed Sgr A West as part of a of 20" or less at 2.7, 5.0, and 8.1 GHz by Downes & survey of galactic H II regions using the new 35 km Martin 11971J, Balick & Sanders {1974), and Ekers baseline interferometer of the National Radio Astro [!974|. Two such maps, taken from Balick & Sart- nomy Observatory (NRAO). 2. OBSERVATIONS AND RESULTS The instrument consists of three 26 m telescopes 8085 MHz (3.7 cm), and the lobe separations vary separated by up to 2.7 km, and a new 14 m telescope between 0.2" and 2", depending on frequency and located about35 km southwest of the other dishes on projected baseline length. The system bandwidth is top of a mountain. The interferometer operates 30 MHz (limiting the effective Held of view to about simultaneously at frequencies of 2695 (II cm) and 45"), and the overall system noise is about 0.2 tu in 30 s of integration. The instrument performance is quite stable, with the largest source of systematic er * Operated by Associated Universities, Inc., under contract ror arising from atmospheric effects, especially at low to the National Science Foundation. elevation angles. B. HA1.ICK A R.|. BROWN -»i' S0° A ?6?!> W* __.' I. fïpure /. 'Cleaned' synthesis maps of the Ga'actic Centre at 2.7 and 8.1 GHz taken from Balick A Sanders J1974J. The synihesised beam has dimensions 2" x 7" in position angle JO" at 8.1 GHz: the beam is three times larger at 2.7 GHz. The apparent differences in the structure result principally from the different coverage of the (u. rf plane at the two frequencies, Thr sub-arcsecond structure reported in this paper lies very close to the brightest feature seen in the 8.1 GHz map. "I 1 1 " 1 1 'J SGR-a «AS.-.- 200 SYNTHESIZED APERTURE ISO ws'** - 100 - .!» H t SO «-4 1 1 , L_ 100 ISO U(UIOs> RIGHT ASCENSION Figure 2. The projected baseline coverage and resulting synthesised beam pattern available for Sgr A on the 35 km baselines. Hour angles and baseline lengths are indicated along the ellipses. The axes are u, the east-west, and v, the north-south projections of the baseline, measured in 2695 MHz wave lengths. 37« ellipses at 8.1 GHz are larger by a factor of three end the corresponding beam pattern is three times smaller. iNTi-NSh SUH-AKCSI-.COND STKIXTURI-. IN GALACTIC O-NTFU * *û. osoj- 0 a 0 00 tî_ 1 050h o . o». a «S 2695 MH; û 9 S > Q ô -1 • • 0 • • il ° • ,». 3 80 *> 0 •». J • J t • * a g A 0 —2- # 9 « - <5 • 9 • 6 io 80 0 • A h A ». i A ûj • j a * A • • , * r i 0 9 C • A 0 ô. . S 0 * 9 80 9 • o»« * • • A .'» »A 9* • 4- r " A « 0" +ln +2n +3" -3" -Zh -lh 0ft +t" +2h +3h 1 HOUR ANGLE HOUR ANGLE Figure 3. Observations of Sgr A West ai 2695 and 8085 MHz on lS February {circles) and 15 February (triangles} 1974. Right and left circular polarisations are indicated by filled and open symbols, respectively. The upper, middle, and lower sections of each graph correspond to the 35.2, 33.2. and 33.8 km baselines. Shaded areas indicate thai the elevation angle is less than 10°. The synthesised aperture available for Sgr A and sents a vector average of 5 min of observation. The the resulting beam pal tern are shown at 2.7 GHz in scatter of the points is consistent with that of the Figure 2. Observational results are presented in Fig- calibration sources (which were observed every ure 3. The phase reference position used in (he com- 30 min). No believable evidence of polarisation was puiation of the phases was chosen solely to minimise found, so that the polarised intensity is less than 10% the phase variations at 2.7 GHz. Each point repre- of the total intensity. 3. SOURCE STRUCTURE We now investigate possible configurations for the only small portions of the (u, v) plane, it is difficult source structure. Less emphasis is placed on the to select among the possible configurations. The more 8.1 GHz results in formulating the models because of difficult problems of reconstructing the brightness the relatively greater importance of noise at this fre distribution are discussed later. We first list some of quency. the more obvious features of the structure. There are, of course, an infinite number of source (i) Because of the lack of structure in the data, the models consistent with the data. Since we sample source brightness distribution is simple and con- B- BAI ICK «RI. BROWN s»(s of one 01 two dominant components he icss than 0 I ". then ihe tiiigfitncss temperatuio 1 1 S Oil The component soutces appon unresolved, since Tb exc-eds 10 - K al 17 GH/ and I0"- K at the fringe amplitudes show ItMle Jgnot variation 8 1 GHz. oen though the projected h awl me lengths change b> more than a factor of ihier ui each frequency The problem of determining ihe source hrighwess A conservative upper limit to the angular Jia- disinnulion essentially amount) to finding a source meie; r1 is 0 1" At ihe dislance of ihe Galactic disinbulmn wluch explains the 17 (ill? phas^ <•! Centre (*- lOkpcl. the sourer diameter d is less ^1SU° and does not conflict with the remaining than 10'AU 110 : * pel. data. We have considered models of single and double I ml The distribution of component» is con line J (o a unresolved components. The hesl of ihcr models l" \ 3" legion centred al the phase reference posi- consists of a single-point source displaced about I.3" s 17 1 m a ( = 1-. h :9:64 . 6 south ol the phase reference al a 1050= ' -*- l i50 1*150- i 1 = 28°5°-' 16.38"). Sources outside this region 2'>.2ns + 0.005 . fil9?0 -8°5q'|763" + 0.10" would have shown substantial amplitude and Ttic predicted amplitudes and phases are shown in phase variations at l^GH/. Thus ihe sub-arc - Figure 4. L\cept fm the systematic differences be second structure is coinddem (within the rather tween ihc predicted and measured phases at 17 Gllr. large IR errors* with the cent mid of ihc 10pm the agreement with the data is quite gixnl (the agree extended source and slightly west (0.2* * 0.15s; ment with the 8.1 GIfe data is ihe best of all models of the IR point source number 1 discussed by consideicd >. RiekeiLow J1973]. Other models can be contrived to give a bcltei fit (iv)The loial flux density of the sub-arcsecond struc to the 17 Gib phases. However, all of these models ture. S,,. is approximately O.h fu at 17 GHz and are rather unlikely because they predict amplitudes O.Sfu *t 8.1 GHz. The ratio of fluxes. Sg ,/S-. T. and phases in cunflicl with ihc preseni 8.1 GHz data is-1.3. or previous observations on shorter baselines. (v) Assuming the angular diameter of the sources lo 0.75 a 0.50 E * 0.25 000 -3h -2h -lh Oh +lh +2" +3h 3*1 -2h -|h oh +ln + 2n +3h HOUR ANGLE HOUR ANGLE Figure 4. Predicted (.mpbtude and phase for the source model which gives the best fit to the data (35.2 km baseline). The model is described in the text. The units of amplitude arc arbitrary. Vertical ban denote the range of phases corresponding to the estimated errors in position (shown for 2.7 GHz only}. 4. DISCUSSION The high brightness temperature, small angular second structure unique in the galaxy. Other types of diameter, and intimate association with strong [R and galactic radio sources, such as pulsars or detectable nearby radio continuum sources make the sub-arc- x-ray snurces, resemble the jub-arcsecond structure in ÏNTUVII M'»-AR< SKOND SIHI rrriu IM,AI.A(TK f'rvtKi 265 at mosi one 01 two respects Unfortunately, the mice hase been the sue of energetic processes simrla; nature nf ihis structure ..'annul he ascertained from Us to liir.M- now seen in the quasar Bl. Lac hy Oke &. radio spectrum .is determined by lite present nhecrva- Gunu J19741 ïnd others. The possible reasons lor lions alone Batick & Sdmleis [l')74| have shown such aclivits have recently been reviewed bv Saslav, thai the nearby structure of scale sue about 10 has |I'J71|. an optical depth n-*ar unity between 1 and X OH/, so The nature 'it the sub-arcsecond structure cannm it is probable thai the ratio of fluxes, ^>h | ''^j; 7 he established until observations are suhslanMally — 1 .'. is the result of toicground ansorption at the improved. More complete coverage on baselines lower frequency anil is mil indicative <>t physical con- between 10s and 10* ) is a necessity Preliminary stiiuliom in the stmctiire its-elt VLB observations ,,t Spr A made at ç (»H/ un J h'ise- Die in usual nature of the sub-arcscconi siructure line nt It)*"'> ny Lu [l'^l ani co! aboraiors indi and its positional coincidence with the inner I pc cate a possible detection. Additional VLB observa core ut the galactic nucleus strongly suggests that this tions at different frequencies and baselines, as well as structure is physically associated with the Galactic inlrared and x ray observations of higher spatial reso Centre I perhaps it defines the Galacti. (entre). The lution would be most useful. Hnally. we mite that available information sliows that there exist some since the dimensions of the sub-arcsecond structure intriguing morphological similarities between this arc - I light da>. and since the region in whicn the structure and the more energetic nuclei of iilhcr structure is found is no larger than - 1 light month. galaxies m tenus ni their i_":s and brightnesses. variations m the radio flux and structure arc an inte Sandets & Prendergasl |1974] have hypothesised that resting possibility. although now quiescent, the Galactic Centre may REFERENCES 1. Balick. B. A Sanders. R.H.. lu he published in 6. Rieke. G.H. & Low. F.J.. Astrophys. J. 184. 415 Astrophys. /. 15 August 1 974. (1973). 2. Downes. D. & Martin, A.H.M.. Nature 233. 112 7. Sanders. R.H. & Prendergast. K.H.. Astwphys. J. (1071). 188.489(1974). 3. Ekers. R.D.. private communication. 8. Saslaw, W.C.. Paper delivered at IAU Meeting, 4. Lo. K.Y.. private communication. Sydney, Summer 1973. 5. Oke, J.B. & Gunn, J.E.. Astrophys. J. (Lett. /189, L5 0974). DISCUSSION D. DOWNES: Do you detect anything in Sgr B2. of whether this enormously high value is not caused W3 or Orion? by assigning the profile of the peak of the source to the entire source, which might be larger? Can you B. BAUCK. Jr. Sgr B2 there appears to be some allow for an envelope of the point source in view of weaker structure. In W3 and Orion, as I recall, no your observed pattern? structure was found to a level of three times the noise anywhere in the maps; and at 3o many features do B. BALICK: Ye; Because the fringe spacings at not correlate with known fine structure. We have not 2.7 tnd 8.1 GHz each ,ary by a factor of three, and sufficiently analysed our data in the H II regions yet yet no significant variations in fringe amplitude were (aside from Sgr A), so that I cannot give you a défi observed, it follows that no halo between about 0.2" nitive answer. and 2 " surrounds the sub-arcsecond structure. Of course, one must keep in mind (hat this source is C. ANDRIESSE: You quoted an upper limit to found in the direction of complex structure from the the size of the source, so your brightness temperature H II region in Sgr A West. is a lower limit only. This brings me to the question EXPEC TED INFRARED MOLECULAR LINES FROM THE GALACTIC CENTRE E. Bussoletti iMitulo di Fisica. Universita di Lecce, Italy ABSTRACT L.\net:ted iiilensmcs (at Earth) ol miational II; aie delectable with j rescm infrarsd techniques. Their and HI) lines are computed fm Sgr A and Spr B; observation will provide the first direct estimate nl" clouds. Radio molecular data ate used to compute the masses and of the D/H ratio in very dense clouds. half-widths of these lines. It is shown that some lines . INTRODUCTION Strong H3 lines have been measured m absorption molecules in interslcllar clouds. Ii is then possible to in 15 reddened stars by Spitzerel al. [1°73| with the estimate the intensity of these lines in the rotational OAO Copernicus satellite, as well as two HD lines. wavelength range for dense objects (i.e. n^, > The results provide useful information about the 10* cm"3) like Sgr A and Sgr B2 at the Gulâciic physical conditions which allow the presence of these Centre 2. METHOD OF COMPUTATION The usual mechanism for the production of a line 1.45 x : 0* T * ( — + _L )* cm/s .,-, is collisional excitation followed by spontaneous radi k ation. In the case of Hj and, though less strongly, of HD. the lifetimes of the excited levels are rather lonf the radiative de-excitation is therefore negligible com the average relative velocity between panicles witt: pared to de-exdtalion by collision with the Hz mole masses fi, and ;jj expressed in the mass unit of hydro cules. The collision rate between two levels. J, J' is gen atoms. Tj; is the gas kinetic temperature. As given by hydrogen muiecules in the ground rotational stale probably behave like 'hard spheres' during collisions, Cjy « n n 1 a temperature of Tn = I '0-5 K so that it is possible to The rate ol energy emu led m the transition J - J' is calculate the expected value of a for cloud* whose given by temperatuie T^ is known 170 5 I705 while we may finally wnte Tk (7) I •• ~l nJ (5) minna that for 1\-0 a-0 and for T^ » T0 where the populations are normalised to the densities G - 3 Equations {3) - (7) allow the cmrssivittes for of the species for which calculations are made. H: and HD to be calculated. According lu the OAO In the case of hydrogen, we consider the other results, the observations of the HD lines in nine red relation dened stars indicate a value HD/H] — ÎCF6 In dens* clouds, however. HD should he more abundant, since shielding becomes effective also for rtJ (61 'le it. Obieivaijons of Î Oph by Spiizer et al. |1973| indicate that D/H may vary as :x Iff* < D/H < 2 x IT*. In addition, a ditect measurement of £Cen which takes in account ths fact thai the molecules by Rogsrson & York ( Î973J gives D/H ^ 1.4 x l 3. CALCULATIONS The dimensions of the cloud in front of Sgr A line is seen). We have considered particularly this one have been taken from the measurements of Solomon where also NHj has been detected by Mortis et al. et al. [19721 in the CO lines at 115.271 and [1973] with a large p .ak emission between 20.6 km/s 110.201 MHz. This cloud presents two rpaior fea and 28.9 km/s. The angular size of this cloud is slight tures, the northern one centred at 55 km/s. and the ly difficult to determine exactly because of the low southern one centred a! 20Jcm/s (probably the 1 *C0 intensity expected near the cload boundaries. densest because it is the only one in which the HjCO The diameter is, anyway, in the range 5 • 20' so that IK MOM 11 l.AH 1 INt-S mtlM IHt <.M A(7K ' I M HI T-Stei f*»tant.< Diamctci n»i Sgf A Sf-r H2 io4 SgrH2 raasmo crg/s tm' eig/s cm1 SO) 1.44 x Iff10 ft b X Iff3 1.6Ï x Iff" 3 14 x Iff Slj 2 20x Iff" 3.9 x Iff1 •1.06 x Iff* 1.90 x Iff S2l 5.20» Iff" 1.35 X Iff W» 9.90x lff'° 2.62 x Iff' 2.28 X Iff' 1.24 X Iff RID ].86x Iff" 1.31 xlff' 5.55 X Iff* 6.25 X Iff R<2> 6.63 X Iff" 8.82 x lffJ 9.05 x Iff1" 4.20 X Iff W3I 2.37 x Iff" 3.I1X Iff we have chosen 3 conservative value of IS oc in ih< region of angular extent 5.2 ± 1.5{arcmm)J a lower linear diameter. The cloud is taming as it is clearly limit for Hj molecules 4 x IQ* cm'3 has been lounti shown by the velocity gradient. Under the hypothesis The densest core of Sgr B2 (7.5 ± 2-2 pc) gives an that il is gravitâtionally bounded, the virial theorem estimate of nu > 10*cm*1, corresponding to a total 1 gives as a lower limit of the mass of the cloud mass of about Ï0 MQ. Methylcyanide (CH3CN> M = 3 x 10s Mg, which corresponds to a mean mole millimetTe emission lines detected by Solomon et al. cular hydrogen density t\u ~ 10scm"1. The temper [1973] have a strong peak at VLSR = 60 km/s practi ature may be estimated from the UC l*0 saturated cally coincident with the broader one of HNCO line. The brightness température In the centre of this Ho* -30J Cine) at vj^ * si km/s. This emasion line has to be expected equal to the kinetic tempera over about t' in the central area of SgrB2aHowsa ture in a layer where the optical depth r * I (Solo better estimate of the kinetic temperature mon, 19721; for iaC160, a temperature of up to TflOOK with respect to the old one of 17 K is found. It is quite possible, as is suggested by \ = 150 K. other line observations (CHjCN, Solomon et al., These results, which are in agreement with the 1971), that there is a smaller central core with a previous ones of Morris et al. [1973], suggest rela much higiicr kinelic temperature. We assume for this 3 tively high densiUes (njj, > 10*cm" ) in this small object a dense core whete Tfc = 50 K. core. For Sgr B2 we have considered the recent obser The HNCO, Jfcjtp =4I3 - 3I2 rotational tran vations of Morris et al. [1973] in the NH3 line from sition has recently been detected at 88.24 GHz in the source centred at a velocity of 52km/s. In a SgrB2 by Snyder & Buhl \}913]. Veiy recent t ftrssm i TTI I mcasuiemculs bv llockuip el al 11 «>T41 ot p,,. tin- -, I .iipnlc mnmcm ol HMO, give j value ot /i(, which iv j 11 order «f magnitude laigei than previous^ esii- maied. and revise the mini muni h)diogen density re quired !•• escitr cultisiiHialK IK'XO molecules The 4, , Î,. ha> liletimcs tor spontaneous emission ol otik 1 'Il s m con liait to the longer lifetimes id llie I 4„j 4„, tiansition Tins last une should oiigiiuie * ' ! ' tiotn a less denw region |Sntomon et al . I«>?.*. ! Snvdei & lluhl. I"T:| njj, > 10* cm"-' On the ntlin ; _ ! hand, the 4, i i; iiansiiion musi come liom a -j J smaller and dei v upon (<)'(. whetr the density 2 ' I must he n^. "> 10*cm" ' Tttn laM repion lias hern ! . I considered in our calculations. Table 1 icporls die t ' . physical paraiuelets adopted U t Spi A and Sgr HI | ' | riie values id tin.- orthofpara laiio have been calcu- . I laied according to (-quaiiuit (?l The H; and M[J tltixcA at the hatlli are reported in Table 2 Consider ing the present Itnnis ol IR dcicctots. and asMimiii): a reasonable atmospheric and instrument transmission """ ot s . one obtains a detection threshold ot ] I 5 \ |irM cig/cnY s fut ihe telescope on lite NASA ill! . (-141 aircraft with an integration time of I h The I i : ' line intensities both from Spr A and Spi B2 are le- l j ' purled in l-ipute 1 where the llm-shoU! limit is also I 'j i '' pven- I ' ' I '^s "nc can we* lne ",osl!av()Ura f1'c source loi Figure 1I I hxpeavdill intensitiesi I: of Hi andL HD linesI the lines » 0). R( I >. SI ) and R( 01 is Spr B2 at the Harth for Sgr B2 (full bars) and Sgr A 'broken bars I The arrow represents the deieetiun threshold for I hof integra tion time with the 4. LINE-WIDTH CALCULATIONS The radiu lines detected in Sgr A and Sgr B2 can whe.c tna is the mass of the emitting n^olecule. be used to determine the expected widths of Hj and CH,CN ( the narrowest line! in Sgr B2 and NHj in HD rotational lines. If a line is broadened by thermal Sgi A have Av = 20 km/s and Av = 42 km/s. respec motion of the emitters (described by their kinetic tively. Ii is therefore possible to calculate the res temperature TjJ and/oi by small-scale turbulent pective Doppter temperatures motion of the emi'ting gas (described by the RMS turbulent velocity W by small-scale turbulences. The calculations show that Av = 2(Iog 2) \^~ + | motions The OcippierWkhhi expected Un Mj and 111î ) of Sgr B2, an-* iv » 42. ..i/s m Sgf A m the clouds arc negligible (Sgr B2 .iv-,^ Ï I 5 -r Tlie MPW value» tor H: and HU lines are reported : km/s. Sat A. iv^, » I - 1.5km,'sl. toihai wc may in ihe third and fifth column» of Table 2 We can see he suie that the smalî-scaïe turbulent motions of the that a spectroscupu resolving power R = >,'i> ot gas in the clouds prevail in the line hmademng. Wee R=l5xllJ* is necessary for Sgr B2. and have ihcn assumed Av * 20 km/» m the emi raJ core R = (j 7 x i 0* for Sgr A. 5 CONCLUSIWJS Sahmfîhmeift rstdecular data and the UV resultiss ictesvupe become» Sx 10"*' ct&cm2. so that trie ot ttur OA(J Copernicus uielhie love provided usetuil signal-to-noise ratio for this line is expected ra be 10 information Sur calculating the expected fluxes at the« for i h of integration. haith of Hj and HD rotational lines emitted hy Sgr A\ We noie finally that (he rotational wavelength andSgr (32 'he S<0i. Sth. Ki.lt and R<0t lines arc (h,çe range seem» !o be extremely interesting for future most mi crise m Sgr B2 and are quite easily detectablle measurements. By measuring the relative intensities with the preset!! limitations of IR detecton and airF- of the lines, it will be possible to make direct, inde borne telescopes. pendent estimate» of the total Hj and HD densities. We note that the $12) line could be diteclable Hai of (he real kinetic temperature, and nf the HD/Hj (he ground. In fatt, the detection threshold tor a 2 in abundance istto REFERENCES 1. Bussulelti, E.. Astro». S Astrophys. 23. 125 ». Snyder, LE. & Buhl, D., Astrophys. J. 177. 6)9 (W73). (1972). 2. Bussoleth, E. & Stasinska. G . Astron. & Astro 9. Snyder. LE. & Buhl, D., Moure phys. Sri. 243. phys. in press. 45(1973). 3. Daigamo. A.. Black, J.H..A Weisheil, i X.. Astro- 10. Solomon. P.M.. Jeffem. KB., Pensas. A.A. & phytUti., 14. 77(1973). WUson, R.W., Astrophys. / 168. L107(1971). 4. Daiaamo, A. & Wright, EX.. Astrophys. J, 174, 11. Solomon. P.M.. Scoville. N.Z.. Jeffens. KB.. L49(l°72). Penzias. A.A. A WPson. R.W.. Asimphys. / 178. 5. Mocking. W.H.. Gerry. M.C.L & Winriewisscr.G., 125(1973). Astmphys. J. 187. L89 (1974). 12. Solomon. P.M., Symposium on ln:?rstellar Mole 6. Morris, M., Palmer, P.. Turner. BE. & Zucker- cules (éd. M.A. Gordon, John Wiley & Sons. New m».».. Astrophys. J. 186.528(1973). York). 7. Rogerson. J.B- & York. D.C.. Astmphys. 186, 13. Solomon, P.M., Penzias, A.A.. Jefterts. KB. & L95U973). Wilson, R.H., Astrophys. J. 185. LA3(1973). DISCUSSION A.P. WHUWORTH: You have assured lhal also wSJ begin to become selfshieided and then iu HD/HÎ - 2D/H. Since Hj exists only by shielding niensiiy wS increase. iiielf against the destructive Lymw-btnd n Jiiiion, then HD will be substantially leu abundant tran this. K-W. MICHEL If you consider dust in the clouds, the emissiïity of both Hs and HD will be E. BUSSOLETT1: No, on the contrary, at high reduced by a factor 10-100 compared «ith calcula densities like thou found in Sgr A and SfFB2,BD tions based on colliskmai equilibrium. It ought there- i Hi'ssoitm ii-îe .-»e \er> diltWult indeiecl the molecular H. radi- I- BUSSOl.ETTI 1 have mu. but lh. K.W. Michel jtion with an mstiunieni winch does no! piovidc !i>i has in Munich. They are thin. sk> chopping Also, the de-excilalton tatios lot II* lun* been measured (Jodeit and agree with the KJ- WIl.US: You stated that the oitho.para adopied wiue loi (tie lowest lolalioiiaf level KM (he hydrogen population was tempérai ute sensitive (0 - hi£hei levels, howevei.il is predicted to he appreciably I ~J* KI Tliis would imply that the relative cullison «mailer so that calculations on (he basis ol collisions! line intensities would allow you to determine llic equilibrium might have to he revised. i m ho para population in a source and hence an accu rate temperature detctmination of the source- Is this t Bl'SSOLMTI I agree that the inienstn will correct ' be reduced, hut at least SUM and R((H will still be detectable. h. BUSSOLETTI: Absolutely correct. The detec tion of these lines will allow a direct measurement of M V PI-NSTON Haw you checked that (he lines all these parameters jte ofUii.3ll> Ihin'