No. 60 - -.June 1990

--, Planning the VLTVLT Interferometer J. M. BECKERS, ESO

1. The VlVLTT Interferometer: VLVLTT Reports 44 and 49), the interfero­interfero- approved YLTVLT implementation. P. LemaLena One of the Operating Modes metric mode of the VLVLTT was indudedincluded in described the concept and planning torfor ofoftheVLT the VLT the VLTVLT proposal, and accepted inin theIhe the inlerferometricinterferometric mode of the VLTVLT at

1.1.11 Itsfts Context Adaptive Optics at the ESO 3.6-m Telescope The Very Large Telescope has three differenldifferent modes of being used. As four separate 8-metre telescopes it provides theIhe capabililycapability of carrying out in parallel tourfour different observing programmes, each with a sensitivitysensilivity which matches that of the other most powerful ground­ground- based telescopes available. In the sec­sec- ond mode the light of the four tele-lele­ scopes is combined in a single imageimage making ilit inin sensitivity the most powerful telescope on earth, almost 16t6 metres in diameter if the light losses in the beam eombinationcombination canean be kept low. In the third mode Ihethe light of the four tele-tele­ scopes is combined coherenlly,coherently, allow­allow- This faise-colourfalse-colour photo illustrates the dramatiedramatic improvement in image sharpness whiehwhich is ing interferomelrlcinterferometric observations with the obtained with adaptive optiesoptics at the ESO 3.6·m3.6-m telescope. seeSee also the artielearticle on page 9. unparalleled sensitivity resulting fromtrom I1It shows the 5.5 magnitudemagnilude star HR 6658 in the galacticga/aeUe eluslercluster Messier 7 (NGC 6475), as the 8-metre apertures. In this mode theIhe observed in the infrared L·bandL-band (wavelength 3.5pm),3.Sllm), without ("ullcorrecled",("uncorrected", left) alldand with angular resolulionresolution is determined by the "corrected","corrected, right) the "VL"VLTT adaptive optics prototype" switched on. The diameter of the distance between the telescopes (up to10 uneorrecteduncorrected image is about 0.8 arcseconds, eorrespondingcorresponding to the instantaneousinstanlaneous "seeing"seeing"9 diskodisk. 120 metres), rather than by the resolu­resolu- When corrected, the image sharpness increasesinereases nearly fourfold; the diameter is now only 0.22 tion determined by the individual tele-tele­ arcsec. This corresponds to lhethe diffraction Umitlimit at this wavelength; the diffraction rings are weilwell visible. The improved sharpness reveals that the star is double; the angular distance between scopes (set by the atmosphericalmospheric seeing, visible. The improved sharpness revea/s that t!Je star Is double; the angular distanee betw8en the two eomponentscomponents is 0.38 areseconds.arcseconds. or by the diffraction limit of single Although it is not evident on this picturepieture in whiehwhich theIhe intensity sealesscales have been normalized to 8-metre apertures while using adaptive the same level, theIM eentralcentral intensity of thet!Je eorrecledcorrected image is much higher than that of Ihethe optics or speckle interferometryj.interferometry). uncorrected. SyBy coneentratingconcentrating Ihethe light belter,better, Ihethe effideneyefficiency of the leleseopetelescope is eorrespond­correspond- Following an in-depth study by the VLTVLT ingly inereased.increased. This means that shorter exposure times are possible or thaithat fainter objects can InterferometryInlerferometry Working Group under the be observed than before. chairmanship of P. LenaLfma (published in thatthat timetime inin anan earlierearlier articlearticle inin thethe thethe change-overchange-over fromfrom thethe useuse ofof thethe tiontion planplan andand proposalproposal viewview thethe de-de­ MessengerMessenger(P. (P. Lena,Lena, TheThe MessengerMessenger53, 53, sub-arraysub-array toto thethe fullfull VLTlVLTI requiresrequires aa velopmentvelopment ofof interferometryinterferometry withwith thethe 53,53, 1987).1987). minimumminimum ofof steps.steps. VLTlVLTI toto bebe aa gradual,gradual, step-by-stepstep-by-step one.one. SinceSince thethe acceptanceacceptance ofof thethe VLTVLT AlthoughAlthough suchsuch anan integratedintegrated ap-ap­ TheThe plan,plan, however,however, differsdiffers fromfrom thethe origi-origi­ proposal,proposal, thethe VLTVLT finalfinal definitiondefinition andand proachproach maymay appearappear obviousobvious toto thethe read-read­ nalnal proposalproposal inin somesome aspects:aspects: (i)(i) itit design,design, includingincluding thethe finalfinal sitesite testingtesting er,er, itit isis byby nono meansmeans anan uncontroversial,uncontroversial, arguesargues stronglystrongly forfor aa configurationconfiguration ofof thethe whichwhich willwill soonsoon leadlead toto thethe VLTVLT sitesite obviousobvious philosophyphilosophy toto everyoneeveryone inin thethe 8-metre8-metre telescopestelescopes whichwhich isis moremore op-op­ choice,choice, has been rapidly proceeding. interferometryinterferometry community.community. There firstfirst isis timizedtimized forfor interferometryinterferometry (see(see sectionsection TheThe implementation planning of thethe in-in­ thethe skepticismskepticism by many about thethe actual 3.1), (ii)(ii) itit provides forfor thethe expansibility terferometricterferometric mode isis an essential part availability of thethe 8-metre telescopestelescopes forfor of thethe array withwith more auxiliary tele-tele­ ofof that.that. lnterferometrylnterferometry places itsits ownown interferornetricinterferometric imaging.imaging. Certainly, thesethese scopesscopes andand delaydelay lineslines (to(to be provided requirementsrequirements onon thethe design and location largelarge telescopestelescopes willwill not be available forfor by additionaladditional contributionscontributions by ESO of thethe 8-metre telescopes,telescopes, onon thethe sitesite a significant amount of thethe timetime forfor inter-inter­ member states),states), and (iii)(iii) itit provides forfor choice and development, and in thethe de-de­ ferometricferometric imagingimaging until thethe astronomy thethe incorporationincorporation of adaptive optics inin finitionfinition of thethe observatory infrastructure. community wants toto use them for that.that. thethe auxiliary telescopes.telescopes. InIn addition toto thethe 8-metre telescopes, Before their use forfor interferometricinterferometric im-im­ thethe VLTVLT includesincludes twotwo smaller movable aging will successfully compete inin timetime 1.3 Why Large Aperture 2-metre-class telescopes (the so-called with other uses, a "user-friendly" capa-capa­ Interferometry?Interferometry? auxiliary telescopes), whose design and bility for interferometric imaging with thethe configuration has toto proceed in parallel VLTlVLTI has toto be demonstrated. That will In thisthis context thethe question is some-some­ with thethe others. To aid in thisthis planning a have toto be done with thethe auxiliary tele-tele­ timestimes asked on what is really gained by VLTVLT lnterferometrylnterferometry Panel was formed, scope sub-array, which will also exploit going toto largelarge aperture interferometers.interferometers. whose members represented thethe exper-exper­ ways of reaching thethe maximum possible Doesn't an array of many small tele-tele­ tisetise inin interferometryinterferometry inin thethe ESO sensitivity. Itlt is our conviction that thisthis scopes do as well,weil, or even better? The member countries'.countries1. This report can be done, and thatthat thethe resulting user answer to this question is important be-be­ summarizes the implementation plan of demand for the use of the 8-metre tele-tele­ cause it determines the part of as-as­ the panel for the so-called VLTVL T Inter-Inter­ scopes for interferornetricinterferometric imaging will tronomy at which the VLTlVLTI will be par-par­ ferometer (or VLTI)VLTI) as proposed to ESO. follow. Second, the design of the ticularly useful and for which it should This plan is out of necessity incomplete 8-metre telescopes cannot be op-op­ be optimized. Although an increase in since the site for the VLTVLTremains remains to be timized for interferometry alone. There-There­ collecting area in astronomy is generally chosen. fore, compromises are necessary which thought of as giving an increase in sen-sen­ ripple through to the design of the entire sitivity, this is by no means obvious for VLTI, including the sub-array of auxiliary interferometricinterferornetric imaging. It has been 1.2 Philosophy Followed in the 1.2 Philosophy Followed in the telescopes because of the philosophy argued in fact that little is gained in Implementation Plan argued in fact that little is gained in Implementation Plan described above. Certainly, an inter­inter- limiting sensitivity by the increased Right from the beginning the panel ferometer designed without the con-con­ aperture in the case of multi-speckle, took as the basis for its studies the straints associated with the VLVLTT (site, broadband observations. This is the desire to make use of the unique oppor­oppor- fixed telescopes requiring the use of case at short wavelengths (up to the tunity provided by the presence on one delay lines, alt-az mounts, limited Johnson M band without the use of site of four identical, state-of-the-art number of telescopes, etc.) would in adaptive optics, up to the H band with 8-metre telescopes to do interferometric some aspects be more powerful than the use of adaptive optics),optics). The combi­combi- imaging. Its definition of the VLVLTlTI is thus the VLVLTI.TI. These advantages, however, nation of the fact that the number of inin the first instance instance based on the cohe­cohe- fade in in comparison with the power re­re- photons per speckle is independent of rerentnt combination of the largelarge tele­ tele- sulting from an interferometerinterferometer with tele­tele- the telescope diameter D with the de­ de- scopes. The sub-array of auxiliary tele­tele- scope apertures of 8 metres. crease of the maximum spectral band­band- scopes is truly auxiliary to this goal. ItIt This philosophy isis also directly in tune width which can be used with largerlarger serves two main functions. First, it com­com- with that of the VLVLTT Proposal in which apertures results in a very slow increase plements thethe main-array of 8-metre tele­tele- twotwo movable auxiliary telescopes are at visible wavelengths in sensitivity, itit 1 3 scopes toto give more interferometric "joined""joined" toto thethe 8-metre array with the being proportional toto DD"~./ . The VLVLTlTI isis baselines. Second, itit provides for an purpose of giving better (u,(u, v) plane cov­cov- thereforetherefore not weilwell suited forfor thatthat kind of interferometricinterferornetric capability by itselfitself which erage and permanent interferometric observation, unless thethe largerlarger "pre-res­"pre-res- isis available 100 % of thethe time.time. This func­func- usage. lt It is therefore perhaps not sur­ sur- olution" provided by thethe individualindividual titionon isis of use not only when thethe fullfull prising that thethe panel's implementationimplementation 8-metre telescope apertures is of impor­impor- powerpower of thethe 8-metre telescopestelescopes is is notnot plan resembles closely thatthat of thethe pro­pro- tancetance forfor thethe astronomical observation. neededneeded forfor the the observations being being posal, going mostly intointo a more refined Things change when spectral resolutionresolution carriedcarried out, butbut also during the impor­impor- definition of thethe array componentscomponents tak­tak- largerlarger thanthan a fewfew hundhundredred isis wanted. InIn tatantnt initial initial phases phases of thethe VLVLTI,TI, forfor thethe inging intointo account thethe need toto optimize thatthat case case thethe sensitivitysensitivity of the multi­multi- 2 commissioningcommissioning and debugging of thethe performance of thethe array forfor both on­on- specklespeckle observations increases increases as DD2,, interferometer.interferometer. The latterlatter resultedresulted inin thethe axis and off-axis operation. The im­im- makingmaking itit an importantimportant goal forfor thethe VLVLTI.TI. desiredesire toto incorporateincorporate thethe VLVLTlTI sub-arraysub-array plementationplementation planplan sharesshares suchsuch featuresfeatures LargerLarger gainsgains withwith telescope telescope aperture aperture intointo thethe main-arraymain-array inin suchsuch a a wayway thatthat withwith thethe originaloriginal proposalproposal asas thethe numbernumber resultresult inin thethe singlesingle specklespeckle modemode whichwhich andand sizesize ofof auxiliaryauxiliary telescopes,telescopes, thethe em­em- occursoccurs without without adaptive adaptive opticsoptics inin thethe phasisphasis onon longlong wavelengthwavelength coverage,coverage, aa JohnsonJohnson NN bandband andand above, above, andand withwith the VLT adaptive optics at wavelengths 1' TheThe VLVLTT InterferometryInterferometry PanelPanel isiscomposed composed 01of J.J.M.M. significantsignificant (>(>3 3 arcsec)arcsec) interferometric interferometric the VLT adaptive optics at wavelengths Beckers,Beckers, R.R. Braun,Braun, G.G.P.P. DiDi Benedetto,Benedetto, R.R. Foy,Foy, R.R. field-of-view,field-of-view, beam beam combination combination in in air, air, asas shortshort asas thethe HH oror KK bands.bands. InIn thesethese Genzel,Genzel, L.L. Koechlin,Koechlin, F.F. Merkle,Merkle, and and G.G. Weigelt,Weigelt, useuse ofof delaydelay Iineslines withwith aa longlong stroke,stroke, andand domainsdomains thethe sensitivitysensitivity increases increases pro­pro- withwith A.A. Labeyrie,Labeyrie, P.P. Lena,Lena, J.-M.J.-M. Mariotti,Mariotti, and and D.D. commoncommon usageusage ofof beambeam combinercombiner (and(and portionalportional toto DD~4 forfor anyany spectralspectral band­ band- DownesDownes asas consultants,consultants, and and D. D. Enard,Enard, M.M. Faucherre,Faucherre, H.H. vanvan derder Laan,Laan, andand M.M. TarenghiTarenghi asas probablyprobably delay delay lines)lines) forfor 8-metre 8-metre and and width.width. TheThe entireentire infraredinfrared regionregion isis there­there- observers.0bSe~erS. auxiliaryauxiliary telescopes.telescopes. BothBoth implementa-implementa- forefore anan importantimportant regionregion forfor thethe VLVLTI.TI. AsAs 2 2.2. TheTheVL VLTT Interferometer: Interferometer: AreAre WeWe ReadyReadytor for It?It? lRS 7 2.2.11 CurrentCurrentEfforts Effortsin inOptical Optical t------< InterferometriclnterferometricImaging Imaging ]" FigureFigure2 2summarizes summarizesthe theproperties properties ofof existingexisting opticaloptical interferometersinterferometers as as weilwell asas thosethose inin thethe construction construction andand plan­ plan- lRS IGNE ningning stages.stages.There There areare atat thisthis momentmoment 66 ~--- operatingoperating interferometers interferometers available available \\\ IRS IGC (GI2T,(G12T, 12T,12T, MARKMARK 111,Ill, MMT,MMT, Soirdete, Soirdete, Sydney).Sydney). TheThe interferometersinterferometersshown shownare arebroad­ broad- bandband amplitudeamplitude interferometers interferometers only, only, andand dodo thereforetherefore not not include include thethe nownow discontinueddiscontinued Culgoora Culgoora intensity intensity inter­ inter- ferometerferometer and and thethe 10.610.6 [!mvm BerkeleyBerkeley heterodyneheterodyne interferometer. interferometer. All All inter­inter- ferometers,ferometers, ex exceptcept for for thethe MMT,MMT, areare non-monolithicnon-monolithic interferometersinterferometers (with(withthe the telescopestelescopes on on separateseparate mounts)mounts) requir­requir- inging pathlengthpathlength adjustments adjustments using using e.e. g.g. delaydelay lines. lines. AllAll existing existing interferometers interferometers routinelyroutinely acquire acquire fringes, fringes, oftenoften withinwithin minutesminutes and, and, when when weil well engineered, engineered, limb angle 30° shortlyshortly afterafterthe thestart start ofof thethecommission­ commission- ingingof of thethedevice. device.Technically, Technically,the theviabili­ viabili- ,» tyty ofof opticaloptical interferometryinterferometry hashastherefore therefore V/~· beenbeen amplyamply demonstrated.demonstrated. TheseThese exexist-ist­ S inging interferometers,interferometers, generallygenerally ofof a a pro­pro- totypetotype nature,nature, havehave givengiven usus thethe confi­confi- dencedence and and expertise expertise needed needed toto gogo onon ;,/V::,o<>I>" withwith the the many many second-generation second-generation y? el..::'e machinesmachines shownshown inin FigureFigure2, 2, whichwhich areare ~\-'t ~,~ nownow underunder constructionconstruction oror onon thethe draw­draw- L inging board.board. » IQ InIn contrastcontrast toto mostmost existingexisting first-gen­first-gen- \: erationeration interferometers,interferometers, whichwhich focussedfocussed Figure 1: Contour map of the Galactic Centre in the Johnson K band (2.2 ym) with an angular Figure 1: Contour map of the Galaetie Centre in the Johnson K band (2.2 11m) with an angular onon stellarstellar size,size, binarybinary star,star, andand as­as- resolutionresolution ofof approximatelyapproximately 0.70.7 arcsec.arcsec. TheThe GalaetieGalactic CentreCentre isis thoughtthought to to eoineidecoincide with with thethe trometrietrometric observations, observations, these these second­second- loeationlocation ofof IRSIRS 1616NW/Sgr NW/SgrAe.A *. Superposed Superposedis is thethelight light eurvecurvedue due totoan anoeeultation occultation byby thethemoon moon andand thethe resultingresultingreeonstruetion reconstruction ofof thethe finefinestrueture structure inin thetheIRS IRS 1616area area (shaded(shadedareas areas andand dotsdots generationgeneration devices devices emphasize emphasize two-di­two-di- inin thethe eirele). circle). TheThe angularangular resolutionresolution providedprovided atat thisthis wavelength wavelength byby thethe individualindividual 8-metre8-metre mensionalmensional imaging imaging using using a a number number ofof teleseopestelescopes (055(055 arcsec)arcsec) equalsequals half half thethe dotdot sizessizes shownshown at at IRSIRS 16NE16NE andand IRSIRS 16E.16E. TheThe simultaneoussimultaneous baselines, baselines, phase phase c!osure closure resolutionresolution ofof thethe VLVLTlTI exeeedsexceeds thatthat byby aa faetorfactor ofof 1515 (004(004 arcsec).arcsec). CourtesyCourtesy R.R. Genzel.Genzel. techniques,techniques, and and other other imaging imaging methodologiesmethodologies taken taken from from image image syn­ syn- thesisthesis effortsefforts inin radioradio astronomy.astronomy.

2.22.2 OpticalOpticaland and RadioRadio anan exampleexample ofof its its potential potential application,application, dividualdividual 8-metre 8-metre telescopes, telescopes, thethe VLVLTlTI Interferometry:Interferometry: FigureFigure 11 showsshows anan intensityintensity mapmap inin thethe KK willwill increase increase thethe angularangular resolutionresolution withwith SimilaritiesSimilaritiesand and DifferencesDifferences bandband ofof thethe GalacticGalactic Centre,Centre, anan areaarea ofof anotheranother factorfactor ofof 1515 usingusing thethe veryvery highhigh particularparticular interest interest atat the the VLVLTT location.location. sensitivitysensitivity comingcoming fromfrom thethe 8-metre8-metre TheThe VLVLTlTI willwill rely rely stronglystrongly onon thethe ex­ex- TheThe presencepresence ofof thethe veryvery brightbright compactcompact aperture.aperture. ThisThis sensitivitysensitivity will will bebe furtherfurther pertisepertise gained gained with with interferometric interferometric im­im- sourcesource IRSIRS 7,7, onlyonly 55 arcsecarcsec awayaway fromfrom enhancedenhanced byby thethe possibilitypossibility of of realreal timetime agingaging in in radio radio astronomy astronomy withwith inter­inter- thethe GalacticGalactic Centre, Centre, allows allows accurate accurate sensingsensing of of thethe position position ofof thethe inter­inter- ferometersferometers like like thethe WesterborkWesterbork array,array, sensingsensing of of thethe atmosphericatmospheric wavefront wavefront ferometerferometer fringes fringes on on IRSIRS 77 whichwhich is is thethe VLA,VLA, MERLIN,MERLIN, thethe VLBIVLBl networks,networks, disturbancesdisturbances needed needed forfor thethe VLVLTT adap­adap- probablyprobably unresolvedunresolved byby thethe VLVLTI,TI, oror andand thethe AustraliaAustralia Telescope.Telescope. BothBoth opti­opti- tivetive optics.optics. ThisThis willwill resultresult inin directdirect veryvery anotheranother unresolved unresolved object object in in IRSIRS 16,16, calcal andand radio radio interferometryinterferometry relyrely onon thethe highhigh angularangular resolutionresolution imaging imaging (.055(.055 andand subsequent subsequent fringe fringe tracking. tracking. This This simultaneoussimultaneous measurement measurement ofof the the am­ am- arcsec)arcsec) ofof thethe entireentire IRSIRS 1616 regionregion (size(size allowsallows longlong exposures,exposures, whichwhich givesgives sig­sig- plitudeplitude andand phasephase ofof interferenceinterference fringesfringes ofof thethe isoplanaticisoplanatic patchpatch ==2020 arearcsec)sec) nalsnals exceeding exceeding thethe detector detector read-outread-out overover aa numbernumber ofof differentdifferent baselinesbaselines asas withwith thethe individualindividual 8-metre 8-metre telescopes. telescopes. noisenoise eveneven when when usingusing highhigh spectralspectral theirtheir basic basic observable. observable. Aigorithms Algorithms for for ThisThis by by itself itself demonstrates demonstrates a a veryvery im­im- resolution.resolution. TheThe GalacticGalactic CentreCentre providesprovides derivingderiving astronomicalastronomical imagesimages areare there­there- portantportant feature feature of of thethe useuse of of a a large large perhapsperhaps thethe finestfinest demonstrationdemonstration ofof thethe forefore veryvery similar,similar, ifif notnot identical. identical. TheThe telescopetelescope forfor interferometryinterferometry because because it it VLVLTlTI power,power, and and of of thethe advantagesadvantages waysways toto arrivearrive atat the the measurementmeasurement of of allowsallows thethe "pre-resolution""pre-resolution" ofof featuresfeatures inin gainedgained withwith itsits largelarge apertures.apertures. ItIt isis how­how- thethe interferenceinterference fringes fringes areare howeverhowever aa complexcomplex target target like like thisthis one.one. StartingStarting everever notnot unique,unique, similar similar examples examples can can veryvery different.different. ItIt isis instructive instructive toto com­com- withwith thethe well-resolvedwell-resolved imagesimages ofof thethe in-in- bebe givengiven forfor otherother objects.objects. parepare thesethese differences.differences. 3 1000,------, near the Galactic Centre (Fig. 1) for fringe position monitoring or tracking. OVLA U) Radio interferometers limit themselves LJ.J o Z generally to one Airy disk using one :::::; LJ.J "feed", although multi-feed systems us­us- U) ;a 100 ing a few Airy disks are now in develop­develop- I­ ment. Z LJ.J Radio and optical interferometry thus Cl Z CHARA share much, including the intellectual LJ.Jc.. BOA LJ.J ou challenges associated with developing Cl /',A ERLANGEN CHARON MMT NOAO VLT high-resolution imaging techniques, but Z 10 ERLANGE$ CHARON0 • A/', ...A • 0 COAST USNO also differ in many aspects. Initial ...A o • • differences relating to the different '"LJ.J I3T13T IOTA GI3T languages and cultures of the two fields a:l MARKill /', /', ~ A ::J . of endeavour have been resolved, and a Z fruitful interaction and active participa­participa- • SOlR D'ETE GI2T SYDNEY IRMA I~T SOIR D'ETE GI2T COLUMBUS 1 • _ - o0 tion has developed. SUSI • • 0.01 0.1 1.0 .. 10. 100. 2.3 Adaptive Optics: 2 TOTAL COLLECTING AREA (m(m2)) An Important Part of the VLVLTlTI Figure 2: Properties ot of Optical Interferometers. Large filled symbols represent existing The largest gains in sensitivity of the taciliUes,facilities, sma" small filled symbols those under construction, and open symbols those being VLVLTlTI will come from the incorporation of planned. eircles Circles torfor maximum baselines under 100 metres, triangles torfor maximum baselines between 100 and 300 metres, and squares torfor maximum baselines above 300 metres. adaptive optics which will make the tele­tele- scopes diffraction limited at near in­in- frafraredred wavelengths (=2 [.lm).ym). All radia­radia- tion from an unresolved source col­col- The most obvious difference results of c10sureclosure imaging, also in this multi­multi- lected by the 8-metre telescopes will course from the very large difference in speckle case. In the diffraction limited, then be combined in phase, in the area wavelength or frequency. This differ­ differ- or single speckle mode, the relative of a single speckle of the size of an Airy 5 ence amounts to about a factor of 10105. . fringe phase is weilwell established and can diskodisk. The recent spectacular success The much shorter wavelengths in optical be directly measured. Another differ­ differ- with the VLVLTT adaptive optics prototype interferometry places on the one hand a ence caused by the atmosphere is the developed in a collaboration of French much higher demand on the dimension­dimension- rapid variation of the fringe phase with research institutes and ESO (see F. al stability and dimensioning of the time, in as liHlelittle as 10 milliseconds at Merkle et al., in the Messenger No. 58, array, but on the other hand allow angu­angu- visible wavelengths. This implies the use p. 1, and also on page 9 in this issue) lar resolutions comparable to that of the of many observations with very short promises the successful incorporation VLBIVLBl networks over baselines of only integration times, which sets a serious of adaptive optics in the VLVLTT early in its 100I00 metres. The much higher frequency limit to the sensitivity of optical inter­inter- commissioning. Its application will pre­ pre- of optical radiation (10(lo44 to 10lo66 GHz) ferometers. dominantly be determined by the availa­availa- eliminates the use of heterodyne tech­tech- Then there are differences resulting bility of stars within the common-phase nologies with their limited bandwidth from the different treatment of the radia­radia- field-of-view, or the so-called isoplana­isoplana- «(< 1 GHz), except at the lower frequency tion. Detection techniques at optical tic patch. Wavefront sensing in the visi­visi- end and when high spectral resolution wavelengths are photon-noise limited ble and near IR (2 [.lm)km) will result in full 4 observations (R > 10lo4)) are needed. except at near-infrared wavelengths sky coverage at about 5 [.lmym wavelength Also, whereas in radio interferometry where readout noise still dominates. At and above, and major sky coverage at heterodyne techniques allow the use of radio wavelengths detection noise is al­al- shorter IR wavelengths (e.(e.g.g. 100100%% for electronic delays to compensate for the ways detector Iimited. limited. The difference in the central areas of the Milky Way at varying pathlength differences, optical noise characteristics necessitates 2 [.lm).ym). Present experiments using artifi­artifi- interferometry has to use optical delay differences in measurement reduction cial, laser-generated stars for wavefront techniques. techniques. Another difference is the sensing, promise to extend full sky cov­cov- Also the effects of the earth atmo­atmo- ability at optical wavelengths to build erage of adaptive optics systems to sphere are very different. Only at the interferometers with a wide interferome­interferome- shorter wavelengths (1 [.lm).ym). 2 very longest wavelengths will the VLVLTT 8­8- tric field-of-viewfield-of-view2,, giving interference These lower wavelength limits to the 4 metre telescopes be diffraction limited, over a field comprising many (> 10104) ) Airy utility of adaptive optics refer to the whereas this is the case for all radio disks, allowing e.e.g.g. the use of IRS 7 combination of all the collected radia­ radia- telescopes. The VLVLTlTI will therefore tion in a single speckle. But at shorter either work in the so-called multi-speck­multi-speck- wavelengths an adaptive optics system le mode at the very short visible 2 In the following I will distinguish c1early clearly between built for e.e.g.g. 2 [.lmym (as is planned for the so-called interferometric intetferometric and unvignetted field-of­field-of- wavelengths, orOr use adaptive optics to views. For an unvignettedunvianetted field-of-view the lightliaht VLVLT)T) will not suddenly fail to function, make the telescopes diffraction limited from the differentdifferent-~artsparts of the entrance pupil instead it will become a so-called partial at the longer near-IR wavelengths. In the arrives at the beam-combining stationStation unvignet­unvignet- adaptive optics system. In this mode, ted, but not necessarily in a condition to allow multi-speckle mode the fringe phase ted, but not necessarily in a condition to allow computer simulations show that a frac­frac- interferometry between the different telescopes. varies across the seeing image on the An interferometric field-of-view has to be unvig­unvia- tion of the light (5 to 10% at visible speckle scale. Recently developed netted, but in addition has to combine the rays wavelengths) will still be combined in a methods using bi-spectralbi-spectrai image analy­ from the different telescopes in phase (within a single central bright speckle with the sis (or speckle masking) allow the mea­mea- fraction of a wavelength, the so-called "phased rest remaining distributed over the mul­mul- field-of-view") or coherently (within the coherence surement of the relative phases for the length, resulting in fringes, the so-called "coherent ti-speckled seeing image. Even this different baselines, needed for phase field-of-view"). minor concentration in the partial adap-

4 tive optics case can be shown to en­en- hance the sensitivity of the VLVLTlTI at shor­shor- ter wavelengths very much. As is the case for full adaptive optics at near-IR wavelengths, it is realistic to expect the availability of partial adaptive optics for o o visible light, covering a major part of the sky, early in the lifetime of the VLVLT,T, since they use the same wavefront sensing and correcting systems.

o o 3. The VLVLTT Interferometer: Current Plans

3.1 The Array of 8-metre Tele­Tele- scopes • • o o As described al already,ready, the philosophy • in the planning of the VLVLTlTI focusses on the optimum implementation of the array of the four 8-metre telescopes. • Therefore, that's what will be described first. o o

TelescapeTelescope Configuration ...... :.;> The quality of full two-dimensional in­in- terferometric imaging very much de­ de- pends on the simultaneous availability o o ...... ::::" .... of many interferometer baselines in all directions of the compass. It is impor­impor- tatantnt for interferometry with the VLTIVLTl ······c... to optimize the configuration of the '---- 8-metre telescopes in this respect even 0=-25° in the presence of movable smaller tele­tele- o o scopes. The reasons for that have to do with both the sensitivity of the VLTlVLTI and Figure 3: Proposed configuration of the VLVLTT 8-metre telescopes and the resulting (u, v) plane with its potential for being used in a coverage for different declinations ö6 and for zenith distance angles up to 60 degrees. The base wide interferometric field-of-view mode. of the trapezoid has a length of approximately 120 metres. North is up. At infrared wavelengths, where the te­te- lescopes will be diffraction limited, the maximum sensitivity in the imaging mode of an interferometer using differ­differ- redundant spacings resulting therefore How to Get the Light to the ent aperture telescopes results from in only 3 or 4 simultaneous baselines in Combined Coherent Focus? matching the size of the Airy disks. That a direction which makes two-dimen­two-dimen- results in different image scales, and sional imaging virtually impossible, Figure 4 shows the way in which the results in a "zero" field-of-view (re­(re- especially for regions at the lower decli­decli- light from the individual telescopes will stricted to the size of the Airy disk). The nations like the Galactic Centre (Fig. 1). be combined in the VLVLTlTI beam com­com- sensitivity for on-axis interferometry be­be- The VLVLTT Interferometry Panel therefore biner. comes in that case proportional to 02dD2d2,2, strongly argues for a quadrilateral con­con- At each coude focus of the tele­tele- where d equals the diameter of the figuration for the VLVLTlTI approximately in scopes the relay optics create an afocal smaller telescope. With a d = 180 cm the form of an equilateral trapezoid. Fig­Fig- beam with a diameter demagnification auxiliary telescope this results in a 20 ure 3 shows the configuration which is M of 100, resulting in an 8-cm diameter times lower sensitivity as compared with suggested and the resulting (u, v) plane horizontal light beam being sesentnt to the the use of a pair of 8-metre telescopes. coverage for different declinations o.6. beam-combining system. The combina­combina- When Airy disks are not matched (e.(e.g.g. This array has a total of 6 simulta­simulta- tion of the light in an interferometer has when a wide interferometric field-of­field-of- neous, non-redundant baselines and re­re- to occur according to stringent condi­condi- view is wanted) and when working at the sults in a good two-dimensional (u, v) tions if the performance of the inter­inter- shorter wavelengths, the sensitivity is plane coverage for objects anywhere in ferometer is not to be compromised. To much larger (100(1 00 times and more). the southern sky. These properties are maintain maximum fringe contrast, the For observations of the faintest ob­ob- liHlelittle dependent on the precise orienta­orienta- optics has to be of high quality and the jects, it is therefore very important to tion and baseline length of the array, so polarization effects (retardation effects have access to the array of 8-metre that it can be fitted to the VLVLTT site. Site and direction changes) have to be iden­iden- telescopes optimized for interferometric considerations will determine however tical in all light paths. The requirement imaging. The array as described in the the final configuration chosen, as will be that the rotation of the polarization di­di- VLVLTT proposal is, however, far from op­op- the estimates of the deteriorating effects rections have to be identical also results timum. It consists of the four telescopes of the wind flow of telescopes on its in identical orientations of the combined in an approximate EW line, with very neighbours. More on this later. imagesirrlages as weilwell as of the exit pupils. This

5 insensitive to tilts and displacements of the Cat's Eye optics. Because the EW distances between the telescopes amount to as much as 120 metres, long tracks for the delay lines will be needed. These 60-metre-long tracks combined with the requirements for the size of the optics, their smoothness and accuracy of motion, as weilwell as their dead reckon­reckon- ing positioning pose a major challenge to the implementation of the VLVLTI.TI. The size of the Cat's Eye is determined by the unvigneUedunvignetted field-of-view required. TO BEAMCOMBINER Because of the M = 100 times angular magnification 8 arcsec on the sky re­ re- sults in 1/250 radian in the interferome­interferome- ter tunnel. With a pupil image as far as perhaps 75 metres away, this results in ... a beam size on the Cat's Eye entrance ... DL ' ... DL and exit of 38 cm diameter (8 cm inher­inher- DL I" I... DL I... J ent on-axis beam diameter, combined with 30 cm beam expansion). For a low­low- er cost alternative, a 2-arcsec unvignet­unvignet- Figure 4: Beam-eombiningBeam-combining seheme scheme proposed for the VLVLTI.TI. The afoealafocal light beams from the eoudecoude foeifoci of eaeheach of the four individual teleseopestelescopes are relayed to the interferometer tunnel (the ted field-of-view is also under consid­consid- long rectangular horizontal box) in underground light tubes loeated located at right angles to the eration with a 15.5-cm beam diameter. interferometer tunnel. The latter eontainscontains the delay lines (DL) for pathlength adjustment. The The small secondary mirror MMAA in the output of the delay lines is relayed to one of two beam-eombiningbeam-combining laboratories loeatedlocated on delay line can serve a number of other either side of the interferometer tunnel. functions. In the MARK IIIIll interferometer it is mounted on a piezo-electric ac­ ac- tuator so that it can be used for rapid, small-pathlength adjustments. Also for a is an important condition if the VLVLTITI is to optical pathlength in the beam-combin­beam-combin- number of reasons it is desirable to be operated in the wide interferometric ing optics from the geometric path­path- make an image of the pupil at the en­en- field-of-view mode. The proposed length due to the finite refractive index trance of the beam combiner. By mak­mak- beam-combination scheme follows of air. Lightpath differences in air of 100 ing MMAA curved it can do that without these beam-combination conditions all metres will occur, resulting in changes affecting the image relay or the afocal the way from the telescope Nasmyth of as much as 20 mm, a change which is character of the optics. Since the delay focus to the beam combiner. wavelength-dependent, thus complicat­complicat- line moves in position this curvature has Beam combination in the VLVLTITI will ing broad spectral band observations. to be variable making it a "zoom mirror". occur in air. This decision is based both To compensate it, the VLVLTTwill will use re­re- Techniques exist for accomplishing this. on arguments related to cost and opera­opera- fractive optics of moderate size. tional complexity of an vacuum system The Beam-combining Station(s) of this size, as weilwell as an evaluation that oescriptionDescription oftheof the oe/ayDelay Lines the effects of air in the light path can be Interferometriclnterferometric beam combination managed at an acceptable level. There Figure 5 shows the optical schematic can take many forms including combi­combi- are five effects of concern: (i) image of the Cat's Eye delay line optics which nation in the pupil plane, in the image deterioration due to seeing for on-axis is envisaged for the VLVLTI.TI. plane, and electromagnetic interference beams. This effect is lessened because The afocal light beam entering from in the coupling between single-mode of the large demagnification (M = 100) of the left is imaged by MBME on MMA,A , and fibers. Each way has its advantages and the beam diameter making the effective recollimated by MBME to exit towards the disadvantages, and the mode chosen Fried's parameter rr, o M = 100 times left. Its dimensional and angular charac­charac- depends often on the type of observa­ observa- larger, (ii) deterioration of the isoplanatic teristics are preserved, and are quite tions wanted. Other forms of beam patch size due to the increase in angles by M = 100. An evaluation indicates that this effect is just acceptable for the in­in- terferometric field-of-views under con­con- sideration, provided that the seeing is carefully managed, (iii) pistoning of the light phase due to seeing, even if the 750 effective r r, 0 is large. These phase varia­varia- tions have to be compared to those of the free air above the telescopes, and I can be made small and slow enough by ------;-+1.------====-WMB~ shielding the light path from the wind, (iv) scintillation effects, which disappear +------~2500------when the pupil is reimaged onto the Figure 5: OptiealOptical diagram of the Cat's Eye delay line opties.optics. A Cat's Eye looks very muehmuch like a beam combiner, and (v) the so-called teleseopetelescope with MB as the parabolicparabolie primary mirror, and the little mirror MMAA loeatedlocated in the prime "longitudinal chromatic aberrations" aberrations".. foeusfocus as the seeondary secondary mirror. The dimensions of this delay line are for an 8-aresee 8-arcsec The laUer latter result in the change of the unvignetted field-of-view. A 2 arcsec field-of-view requires about half the size. 6 (ii)(ii) forfor wide interferometric interferometric field-of­field-of- view operation it it is necessary toto pre­pre- serve thethe pupil configuration in detail fromfrom thethe entrance toto thethe exit pupil. This places stringent but realizable require­require- ments on thethe locationlocation of thethe pupil im­im- ages, a locationlocation which changes with time, as the entrance pupil as seen from the star, changes with earth rotation. Motion of the MM, q mirrors isis more com­com- plex now and thethe beam-combining tele­tele- scope has toto be largelarge enough in in aper­aper- tureture toto cover thethe area of thethe VLVLTlTI site demagnified by M = 100, resultingresulting inin an approximately 180-cm diameter mirror.

3.2 The Auxiliary Telescopes So far the use of the 8-metre tele­tele- scopes has been emphasized and the definition of the VLVLTlTI main-array has been based on it. As described inin sec­sec- titionon 1.2, the definition of the sub-array of smaller 2-metre-class auxiliary tele­ tele- scopes (d = 180 cm isis assumed here) isis based on itsits incorporationincorporation intointo the main­main- array. That results both inin an ease of change-over from the sub-array to the main-array, in a commissioning and de­de- -L---: bugging of the VLVLTlTI using the always available sub-array, and in a maximizing of the number of affordable auxiliary te­te- lescopes given the limited budget avail­avail- able for the VLVLTI.TI. This results logically in the following definition of the VLTlVLTI sub­sub- , , , ! , , , array (or VISA). o 15 30 45 60 75 90cm

Mp Telescope Configuration Figure 6: Possible eonfigurationconfiguration of the on-axis light beams or pupil images at the entraneeentrance of The auxiliary telescopes are movable the beam-combining telescope. The four large dark circles are the beams of the 8-metre the beam-eombining teleseope. The four large dark eireles are the beams of the 8-metre telescopes. It is proposed that they be teleseopes,telescopes, the small ones those of the auxiliary teleseopes. telescopes. The beams/pupil images are relocatable between fixed stations, simi-simi­ positioned by linear movement of the flatf1at mirrors M,,M , whichwhieh send the light horizontally into the p lar as is the case for the radio Very Large beam-combiningbeam-eombining laboratory, and by movement of the flat mirrors MqMq whichwhieh transfers the light Array and for the IRAM millimetre array. downward into the beam-combiningbeam-eombining telescope.teleseope. MqMq is replacedreplaeed by Mq,Mq , in caseease it is desirable to Array and for the IRAM millimetre array. rotate the image and/or pupil over 180180"0 (as is the caseease when combiningeombining telescopesteleseopes locatedloeated on In Figure 7 a possible configuration of opposite sides of the interferometer tunnel). stations for the auxiliary telescopes is shown. In this configuration the auxiliary tele-tele­ scopes share the interferometer tunnel, combination will undoubtedly arise in bining telescope can be determined by the delay linesIines and the beam-combining the future. For the VLTlVLTI it is therefore the actual observation wanted. Exam-Exam­ optics with the 8-metre telescopes. To impossible to define the characteristics plespies are: change over from the 8-metre tele-tele­ of the final beam-combining station (i) for spectroscopy a linear non-re-non-re­ scopes to the auxiliary telescopes re-re­ now. Instead it is proposed that the VLTlVLTI dundant (e.g.(e. g. spacings 10, 20, and quires the insertion or turning of a single provide for two stations, one containing 40 cm of the 8-cm-diameter pupil im-im­ flat mirror. Change-over can therefore an optical laboratory for experimenta-experimenta­ ages) configuration may be optimum. It be done within minutes. The add-on tion, the other containing a fixed beam-beam­ results in a pattern of parallel fringes in cost per auxiliary telescope is limited to combining telescope with an aperture the image plane whose spacing en-en­ the telescope itself and possibly its between 80 and 180 cm. The latter will codes the telescope pair and whose transporter. provide for common user image plane contrast and relative phase can easily interferometric capability, includinginciuding the be examined with a spectrograph simul-simul­ The Auxiliary Telescopes capability for doing spectroscopy and, taneously for many wavelengths. A con-con­ perhaps, wide interferometric field-of-field-of­ figuration like this can use a stationary To simplify the change-over and the view observations. configuration of M,M p and M,,M q , requires coupling to the 8-metre telescopes it Figure 6 shows a possible combina-combina­ only an 80-cm aperture beam combiner, was decided toto use thethe same typetype of tiontion of the light beams on thethe entrance but suffers in respect toto wide interfero-interfero­ coude optics and telescope mounting of thethe beam-combiner telescope. metric field-of-viewfield-of-view operation. Its pupil as used for thethe 8-metre telescopes. InIn The actual configuration of thethe configuration is not preserved, thusthus giv-giv­ doing so one can use again similar or beamslpupilbeams/pupil imagesimages on thethe beam-com- inging a "zero" field-of-view.field-of-view. identicalidentical control systems, imagelpupillimage/pupil/

7 o 0150"b~ additional telescopes (8(8 metres or smal­smal- I 0 0 o 0 I 0 0 00 ler?)ler?) will probably be locatedlocated at different • 0 0 o ' 0 levels,levels, whwhichich does not exclude their use • 8 00 I 0 @ffi 00 88~ ail~o ~~ forfor interferometry.interferometry. ~.~ ~~.~.i.i ~~"~ Fitting thethe VLVLTITI toto thethe VLVLTT Site • • Figure 8 shows a drawing of the VLTI ~ ~ ~~o ~ 4JJ~pm Figure 8 shows a drawing of the VLTl 150 80 0..... LI0 ' 0 • 0!L.8. 0 000 0 0 0 0000 oo~ on Cerro Paranal followingfollowing thethe layoutlayout ~ ~ ~ ~ ~ ~o ~ ~ ~@~ ~ ~o~ 0 0 8 shown inin Figure 7. 8 00 @ @ 0 0 0000 00600 o~~o The actual configuration for thethe VLVLTlTI ~)@ 00 0 0 MO will be chosen on thethe basis of thethe topog­topog- ~~ o@ GD ~OgO 8 o 0 0 ®:J ::ttn raphyraphy of the site chosen for the VLVLT,T, on ~ ~o o 2m+2m 00 00 thethe wind directions, on thethe seeing o~ ~o i 000 o 2m+8m effects resulting from thethe interplayinterplay of thethe o 0 I o 8m+8m ~ ~015brP 0 wind, thethe site plateau and the telescope o 50 structures, and on other VLVLTT site needs. InterestingInteresting questions remain remain especially Figure 7: Left: a possible configuration of the stations for the auxiliary telescopes (small dots). Figure 7: Left: a possible eonfiguration of the stations for the auxiliary teleseopes (smal! dots), concerning the seeing effects which are The assumed loeationlocation of the 8-metre teleseopes telescopes are shown with large dots (now sfightlyslightly presently being analysed (L. Zago, The different from the eonfiguration configuration shown in Figure 4). The fightlight from the auxiliary teleseopestelescopes travels to the interferometer tunnel along the vertiealvertical fineslines whiehwhich eombinescombines the stations,stations. It Messenger No. 59, p. 22). Such analysis antieipatesanticipates therefore that only one auxiliary teleseopetelescope eancan be used per vertiealfine.vertical line. Additional will have to answer the question on stations on the fineslines eonneetingconnecting the 8-metre teleseopestelescopes to the interlerometerinterferometer tunnel eancan also whether the seeing for the 8-metre tele­tele- be envisaged. Right: (u, v) plane eoveragecoverage options for objeetobject at zenith with the stations shown scopes on the downwind end of the left. Note that in this easecase not al!all eoveragecoverage is simultaneous as was the easecase in Figure 3,3. plateau is much worse than, or compar­compar- able to, that on the upwind end (no one expects it to be better!). If itit is, is, the 8-metre telescopes will have to be 10­lo- cated upwind, but at the cost of the polarization orientations become the ranal and perhaps Armazones). The EW probably much worse seeing effects for same, and retardation effects are com­com- dimension of approximately 120 metmetresres the auxiliary telescopes caused by the parable. The auxiliary telescopes in­in- will pretty weilwell be set by the need to wind interactions with the 8-metre tele­tele- clude the option for relatively simple (as space the 8-metre telescopes in that scopes which are now upwind of the compared to the 8-metre telescopes) direction at right angles to the wind. auxiliary telescopes. adaptive optics. From the VLVLTlTI point of view all three sites look acceptable although Armazo-Armazo­ nes has the advantage of a larger NS TTelescopeelescope Transporters 4. The VLTVLT Interferometer: extension as compared to the other WhWhatat Comes Next? Again following the example of the sites for a given EW extension. This VLA and IRAM array, the telescope gives higher angular resolutions in that Implementation of the VLVLTlTI will start transporters will run along railway direction without the need for longer with the site development after the tracks. There will probably be one trans­trans- delay lines. choice of the VLVLTT site. Extended porter per telescope which will lift the For a number of reasons it is advan-advan­ PhaseAPhase A studies of the major compo-compo­ telescope from one station and place it tageous to locate the VLTlVLTI on a flat area. nents of the VLTlVLTI (auxiliary telescopes, on the next with good precision using a On the longer term, large baselines may stations, tracks, transporters, delay kinematic positioning system. The be wanted, which when located in ap-ap­ lines) will be completed early 1991 and transporter will probably carry a wind proximately NS direction, can use the will be followed by their construction. It shield as wellweil as other telescope existing VLTlVLTI delay lines. In that case the is desirable that interferometry using 3 support equipment. Initially it is the in-in­ tention to move the telescopes infre-infre­ quently, like once per night. As experi-experi­ ence with the VLTlVLTI develops, and as calibration techniques are refined, more rapid configurations (a number of times during the night) may become feasible.

3.3 Site Aspects

WhichWhichSite? Site? For the configuration shown in Fig-Fig­ ure 7 a flat plane is envisaged. To keep the length of the delay line as short as possible and to optimize the (u, v) plane coverage itit isis desirable toto have the flat elliptical area with thethe short axis running roughly EW. This can be done at all VLTVLT sites being considered (Vizcachas, Pa- Figure 8: The VLTIVL TI accordingaeeording to thethe layoutlayout shown inin Figure 7, shown on Cerro Paranal.

8 oror 44 auxiJiaryauxiliary telescopestelescopes (2(2 toto bebe funded tion 01of the auxiliary telescopes, a non-non­ InterferometerInterlerometer a facilityfacility whichwhich willwill serveserve outout ofof thethe VLVLTT budget,budget, thethe others others by zero interferometricinterferometric field-of-view, blind both the needs posed by thethe astronomi-astronomi­ additionaladditional contributionscontributions by researchresearch fringefringe acquisition and maintenance, ex-ex­ cal programmes of thethe non-expertsnon-experts inin groupsgroups inin ESOESO membermember countries) countries) and tended wavelength coverage into the interferometry,interferometry, as wellweil asas thethe needsneeds ofof limitedlimited wavelengthwavelength coverage coverage (.45(.45 to ultraviolet, additional auxiliary tele-tele~ thethe experts inin thisthis rapidlyrapidly developingdeveloping 2525 ~lm)pm) willwill startstart soonsoon afterafter thethe commis­commis- scopes possibly at long NS baselines, fieldfield of astronomy. ThisThis isis a talltall task,task, butbut sioningsioningof of thethe firstfirst largelarge telescopetelescope onon the additional delay fines) lines) will evolve over a as itit could bebe donedone forfor radioradio interferom-interlerom­ VLTVLT site.site. TheThe fullfull VLVLTlTI capabilitycapability (includ­(includ- number of years after this, some of it etry, it should also be possiblepossible toto dodo itit atat inging suchsuch featuresfeatures asas thethe inclusioninclusion of thethe requiringrequiring additional resources. The goal opticaloptica! wavelengths.wavelengths. TheThe fieldfield isis readyready 8~metre8-metre telescopes, telescopes, rapid rapid reconfigura-reconfigura- will be to provide early on at thethe VLTVLT forfor itit and thethe opportunity isis here.

HowHow WillWill thethe VLVLTT MirrorsMirrors be Handled?

SchoHSchott isis nownow puHingputting thethe final touchtouch toto thethe buildingbuilding wherewhere thethe facilityfacility toto pro­pro- duceduce thethe ZerodurZerodur VLVLTT mirrormirror blanksblanks isis to bebe installed.installed. MeanwhileMeanwhile SchottSchott isis de­de- velopingveloping thethe variousvarious toolstools andand equip~equip- mentment necessarynecessary forfor thethe casting,casting, anneal­anneal- ing,ing, ceramization,ceramization, machiningmachining andand testtest of thethe mirrormirror blanks.blanks. HandlingHandling inin particu!arparticular isis aa majormajor con­con- cerncern forfor Schott.Schott. TheThe rawraw blanksblanks ob~ob- tainedtained afterafter castingcasting areare considerably heavierheavier thanthan thethe finishedfinished blanksblanks andand are alsoalso aa lotlot moremore fragilefragile becausebecause of the locallocaldefects defects atat thethe surfacesurface which havehave a tendencytendency toto behavebehave likelike perfect crack propagators.propagators. AnAn additionaladditional difficultydifficulty isis thatthat afterafter castingcasting onlyonly thethe top surlacesurface isis physicallyphysically accessible.accessible. SchottSchott hashas thereforetherefore developeddeveloped a specialspecial handlinghandling tooltool basedbased on suction. TheThe photographphotograph showsshows aa smaller-scalesmaller-scale systemsystem developeddeveloped toto handlehandle 4-m­4-m- diameterdiameter mirrors.mirrors. ItIt isis beingbeing testedtested on anan experimentalexperimental lhinthin meniscusmeniscus realizedrealized inin The picture shows the vacuum pumps thisthls typetype of handling device.deviee. EvenEven inin thethe frameframe ofof thethe VLVLTT developmentdevelopment pro­pro- locatedlocated at the top and the large suckingsueking case of power failurefailure thethe systemsystem canean gramme.gramme.This This mirrormirror hashas beenbeen producedproduced cups arranged as a whiffle tree. The safely hold thethe mirror duringduring severalseveral withwith thethe spinspin castingcasting technologytechnology and triangular structure isis used as a vacuum hours. A similarsimilar systemsystem isis likelylikely toto bebe waswas originallyoriginally 4.14.1 mm diameter.diameter. ItIt has buffer. used forfor handling thethe mirror duringduring itsits subsequentlysubsequently beenbeen machinedmachined down to The tests have demonstrated thethe polishing and forfor itsits integrationintegration intointo thethe 3.73.7 mm diameterdiameter andand toto 7.57.5 cmcm thickness. good functioning and the reliability of cell at thethe observatory. D.D. ENARD (ESO)(ESO)

AdaptiveAdaptive OpticsOptics atat the ESOESO 3.6-rn3.6-m Telescope

F.F. MERKLE,MERKLE, G.G. GEHRING,G~HRING,ESO F.F. RlGAUT,RIGAUT, P.P. KERN,KERN, P. GIGAN,GIGAN, ObservatoireObservatoire de Meudon, France G.G. ROUSSET,ROUSSET, ONERA,ONERA, FranceFrance C.C. BOYER,BOYER, LASERDOT,LASERDOT, France

FromFrom April April 1111 toto 16,16, 1990,1990, the VLVLTT vatory in OetoberOctober and November 1989 system was initiallyinitially designed. adaptiveadaptive optiesoptics prototype prototype systemsystem has (see the artiele article by F. Merkle in The A description of thethe prototypeprototype systemsystem beenbeen testedtested atat thethe 3.6-metre3.6-metre lelescopetelescope Messenger 58, 1989) this was the first has been given earlierearlier (Merkle,(Merkle, TheThe onon LaLa Silla.Silla. AfterAfter thethe twotwo preeedingpreceding test test of the adaptive optiesoptics prototype Messenger 57, 1989).1989). TheThe followingfollowing periodsperiods atat thethe Haute-ProvenceHaute-Provence Obser~Obser- system at the telescope for whichwhieh thethe tablelabia summarizes thethe major data:data:

9 thethe theoreticaltheoretical goaIgoal ofof magnitude 12 10to WavelengthWavelengthrange: range: 33 toto 55 miaometremicrometre 13. After Ihethe mechanicaJmechanical integrationintegration ofof partiaJpartialCOl'Tection correction atat shortershorter wavelengths thethe systemsystem atat thethe GassegrainCassegrain focusfocus (see(see DeformableDeformablemi'Tor: mirror: 19 19 piezo-electricpiezo-electric ac:tuatorsactuators Fig.Fig. 1) itit tooktook approximatelyapproximately three hourshours stroke: ± 7.57.5 micJonmicron + toto alignalign itit with thethe telescope,telescope, toto perlOnTIperform hexagonhexagonarrangement arrangement thethe calibration calibration andand initiaJizationinitialization withwith a a activeactivediameter diameter70 70 mmmm real object on the sky, and to get the TipltillTiphilt mirror:mirror: gimbaJgimbal mountmount real object on lhe sky, and to get lhe piezo-electricpiezo-electricactuators actuators first,first, diffraclion-limileddiffraction-limited imageimage onon lhethe WavefrontWavefrontsensor: sensor: ShackShack HartmannHartmanntype type controlcontrol monilormonitor ofof thethe infraredinfrared camera.camera. 55 byby5 5 subaperturessubapertures ThisThis observingobserving runrun at at thethe 3.6-melre 3.6-metre squaresquareconfiguration configuration telescopetelescope was mainlymainly aimedaimed a1:at: 100100by by 100100intensified intensified ReticonReticondetector detector • verifying thethe gaingain expectedexpected from visiblevisible limitinglimiting magnitudemagnitude9 9 adaptiveadaptive opticsoptics with aa largelarge lele­tele- mirrorfor relerencereference source seleclionselection mirror source scope,scope, Computer: dedieateddedicated processotprocessor • measuringmeasuring thethe effects effects ofof partialpartial 6802068020hast host processorprocessor correction by adaptive optics, and InfraredInfraredcamera: camera: 3232by by32 32 InSblnSbarray array correction by adaptive optics. and additionaladditionalchopping chopping mirrormirror • measuringmeasuring thethe isoplanatic isoplanatic anglesangles atat SystemSystemconcept concept: bandwidthbandwidth 1010Hz{lOO Hz (1 00 Hzsampling)Hz sampling) variousvarious waveleogthswavelengths andand seeingseeing con­con- modalmodalcorrection correction dltions.ditions. mirrormirroreigenmodes eigenmodes TheThe intentionintentionof of thisthis shartshort summarysummary isis poIychrornatlcpolychromaticsystem system onlyonly toto givegive thethe readerreader aa first impressionimpression ofof thethe type type andand Quality quality ofof thethe results results recorcled.recorded. AA detaileddetailed analysisanalysis ofof lhethe SomeSome mechanicalmechanical modificationsmodifications had had nitudenitude 99 fOrfor a a 3.6-metre3.6-metre aperture aperture byby moremore than than 5050 highhigh resolution resolution imagesimages toto bebe mademade atat thethe prototypeprototype benchbench atat usingusing asas aa firstfirst stagestage aa proximityproximity focusfocus coveringcovering thethe J-,J-, H-,H-, K-,K-, l-L- andand M-bandM-band thethe CassegrainCassegrain f/8f/8 focusfocus ofof thethe 3.6­3.6- intensillerintensifierand and aa microchannelmicrochannel intensifierintensifier withwith integrationintegration timestimes rangingranging fromfrom ap­ap- metremetretelescope. telescope. InIn addition,addition, thethe limitinglimiting asas thethe secondsecond stage.stage. Further Further improve­improve- proximatelyproximately10 10 secondsseconds toto 1010 minulesminutes­ - magnitudemagnitudewas was improvedimprovedto to aboutabout mag-mag- mentsments areare plannedplanned inin orderorder toto achieveachieve lherethere waswas nono restriclionrestriction inin integrationintegration

FlglKeFigure1: 1: The Theadapti\IfJ adaptiveopties opticsprototype prototype systemsysteminstal1ed installedat atthe thefI8 f/8focus focusof of thethe3.6-m 3.6-mteles«Jpe. telescope.The Therectangular rectangularframe frameis ispart part ofof thetheopticaJ optical benchbenchtllat thatsupports supports thethesystem. system. ToTothe the16ft leftof ofthe thebench benchis is thetheIR IRamlY arraycamero cameraand andon onthe theright rightside sideis is thethewavefront wavefrontsensor sensorsupport. support TheThe 8h!ctronicselectronicsrack rackattached attachedto tothe theJeft leftside sidewall wallof ofthe theCassegrain Cassegraincage cagehouses housespart partof ofthe thefront-end front-endelectronics electronicsof ofthe thesystem. system. 10 FiguraFigure 2: Images of HR 6519 in the L-Band, wifhoutwithout and with the adaptive optics feedback loop activated. rheThe image diameter shrinks from 0.7 arcsec to 0.22 arcsec, which is the diffraction limit in the L-Band (3.5 14m).pm).

time - will take some time and will be brighter component and 5.74 of the the effects of a partial correction by published elsewhere. tainterfainter one. The separation otof the two adaptive optics at shorter wavelengths. ReferenceRaference stars with magnitudes components is only 0.38 arcsecs. Figure 3 displays the image of the down to 9 could be used torfor the wave-wave­ Apart tromfrom the evaluation of theIhe per­per- 4.7 mag star Cla Hydrae (HA(HR 3748) inin the front measurement and a spectacular formance of the system at the J-, H-, K- and L-Band. The equivalent gain inin imageimage quality can already now be wavelengths for which it was designed, seeing in the visible wavelength range reported. it was the aim of this test run to measure during the recording time was approxi- The observed objects include bright, unresolved test objects to verify the per­per- formance of the system, independent of the oblectobject structure. In addition, a number of more complex objects of par­par- ticular scientificscientitic interest were recorded, likelike q'l Carinae, somesame T Tauri stars, and various others. Figure 2 shows the resolution gain F when the real-time feedback of the adaptive system is activated for the ob­ob- ject HAHR 6519 inin the L-band. The un­un- C corrected image (left) has a FWHM of 0.7 arcsec, the corrected (right) has 0.22 arcsec. The object served itself as reter­refer- ence for the measurement of the wave-wave­ front. Its visual magnitude is 4.81. The asymmetry of the uncorrected object is CI I due to a problem with the 3.6-m auto­auto- t guider which was detected during the observations. OuringDuring the real-time at­at- mospheric correction - the seeing was 0.9 arcsec in the visible range - this artefact was compensated in the same way as all other low-frequency tele-tele­ scope aberrations. The corrected imageimage very clearly shows the predicted diffrac­diffrac- tion pattern. JtIt still shows samesome imper-imper­ fectionsfeetions which are due to some print­print- through otof the actuators of the detorm­deform- E able mirror. The images on page 1 show the im­im- - provement in image quality when the Figure 3: Imaginglmaging of the star CIa Hydrae (HR 3748) in the J-, H-, K-, and L-Band with adaptive system isis applied to the double star HAHR optics feedback. T/leThe dramatic image improvement is visible even in the J-Band where the 6658 with visual magnitude 5.24 of the system was undersampling at least by a factor 0'of 2.5. I 11 FigureFigure 4:4: ThisThisimage image showsshows an uncorrecleduncorrected imageimage (lefl),(left), an imageimage corrected by theIhe tip/tilttip/lilt mirror (middle), and an imageimage correctedcorrected byby thethe tip/tilttipllilt andand deformabledeformable mirrormirror ofof thethe objeclobject HRHR 5646 (visual(visual magnitude 3.87) in the K-Band. The object itselfitself served as referencereference forfor theIhe wavefrontwavefront sensing.sensing. TheThe StrehlStrehl ratioratio belweenbetween thethe uncorrecteduncorrected and thethe tilttilt correcledcorrected image improvedimproved by a factor of 1.3, thethe gain toto thethe fullyfully correctedcorrected imageimage isis byby aa factorfactor ofof 3.5.3.5.

matelymately 0.750.75 areseeondsarcseconds FWHM.FWHM. The im­im- H-Band, and Irom from 0.66 toto 0.29 arc-are­ tilttilt mirror inin comparisoneomparison toto aa fullfull correc-eorree­ ageage impravementimprovement isis dramatieallydramatically evident seeondsseconds (limit: 0.07 areseconds)arcseconds) in thethe tion.tion. Figure 4 showsshows anan uncorrecteduncorreeted im-im­ eveneven downdown toto thethe J-BandJ-Band where the J-Band. This improvement at shorter age (left),(Ieft), an imageimage correctedeorrected byby thethe tip/tipI systemsystem waswas undersampling,undersampling, at leastleast by wavelengths will be an important featureleature tilttilt mirror (middle), andand anan imageimage aa faetorfactor ofof 2.5.2.5. ThisThis eorrespondscorresponds toto an torfor interferometryinterferometry with the VLT.VLT. The correctedcorreeted by thethe tipltilttip/tilt andand deformabledelormable improvementimprovement fromfrom 0.560.56 toto 0.23 are­arc- evaluation of the partially corrected im-im­ mirror of01 thethe objectobjeet HR 56465646 (visual(visual seeondsseconds (theoretieally(theoretically smallest possiblepossible ages will help to build an analyticalanalytieal mod­mod- magnitude 3.87) inin thethe K-Band. TheThe ob-ob­ value,value, Le.i.e. thethe diflraetiondiffraction limit:limit: 0.22 are­arc- el for partial correetioncorrection by adaptive op-op­ jectject itselfitself served asas referencereferenee forfor thethe seeonds)seconds) in in thethe L-Band, L-Band, fram from 0.580.58 to ties.tics. wavefront sensing. TheThe seeingseeing inin thethe 0.180.1 8 areseeondsarcseconds(limit: (limit: 0.130.1 3 areseeonds)arcseconds) Another important part of this testtest run visual region variedvaried between 0.70.7 andand inin the the K-Band, K-Band, from from 0.6 toto 0.21 are­arc- was to measure Ihethe eontributioncontribution of thethe 0.85 arcseconds atal thethe timelime ofof thesethese seeondsseconds (limit:(limit: 0.100.10 areseeonds) arcseconds) inin thethe imageimage motion stabilization with thethe tip/tipI measurements. The maximummaximum intensityintensity (Strehl ratio) between thethe uncorrecteduneorrected and thethe tilttitt correctedeorreeted imageimage improvedimpraved byby a factorfactor ofof 1.3, thethe gain toto thethe fullyfully correctedeorrected imageimage isis by aa factorfaetor ofof 3.5.3.5. What'sWhat's NextNext inin Adaptive Optics? This gain isis limitedlimited duedue toto thethe partialpartial DuringDuringthe the pastpast hallhalf yearyear itit hashas been demonstrated that adaptive opticsopties is a correction,eorrection, sincesinee thesethese measurementsmeasurements provenproventechnique technique for high-resolutionhigh-resolution imagingimaging inin the near-infrared domain. The are takentaken inin thethe K-Band atat 2.22.2 micro-micro­ resuJtsresults obtainedobtained withwith thethe VLVLTT adaptive optiesoptics prototype system give only a metre. firstfirst impression impression ofof whatwhat will be possible in the future with systems with Another importantimportant aim waswas thethe mea-mea­ deformabledeformable mirrors mirrors with with severalseveral tens or even hundreds of subapertures, surement of thethe isoplanaticisoplanatie angleangle asas aa comparedcompared toto thethe 1919 actuatorsactuators thethe ESO system has today. functionfunetion ofof wavelength,wavelength, seeing,seeing, andand or-or­ Adaptive optics devices are highly complex systems. The multichannel Adaptive optics deviees are highly complex systems. The multichannel der of01 correction. TheThe system allowedallowed feedbackfeedback loop loop requiresrequires very fastfast and powerful proeessors. processors. Due toto thisthis offset angles between thethe objectobject andand eomplexity,complexity, adaptiveadaptive optiesoptics systems are often eonsideredconsidered as devicesdeviees whichwhieh reference source of up to 35 arc- areare farfar fromfrom beeoming becoming aa general user user instrumentinstrument of an observatory. It has referenee souree of up to 35 are­ frequentlyfrequently beenbeen assumedassumed thatthat onlyonly specially trained operators or the persons seconds.seeonds. involvedinvolved inin thethe eonstructionconstruction 01of thethe system can operate it and that it will As mentioned above, a detaileddetailed anal-anal­ thereforetherefore necessarilynecessarily havehave quitequite aa restrietedrestricted use. ysis of all resultsresults isis nownow underway.undetway. ThisThis However,However, thethe observationsobservations with the VLT adaptive optics prototype system preliminarypreiiminary presentation ofof somesome ofof thethe attheat the 3.6-m3.6-m telescopetelescope havehave now made itit quite elearclear that adaptive optics canean most important results isis onlyonly aabrief brief beeomebecome aa tooltool whiehwhich cancan bebe offered to any observer without special exper­exper- introductionintroduction toto thethe spectacularspectacular improve-improve­ tise. Although the current prototype is operated from three keybords, not tise. Although the current prototype is operated Irom three keybords, not ments whichwhich can bebe expectedexpeeted fromtrom includingincluding thethe infraredinfrared cameracamera acquisitionacquisition system (see the articleartiele by Merkle in adaptive opticsopties at a largelarge telescope.teleseope. thethe MessengerMessenger 58,58, Fig.Fig. 4),4), thethe operation follows a clear proeedureprocedure whichwhieh couldcould be be takentaken overover byby an additionaladditional host computer. All functionsfunetions can be automated without a major increase of the system's complexity. Also the automated without a major increase 01 the system's complexity. Also the Acknowledgements optomeehaniealoptomechanical part,part, which at thethe momentmoment still requiresrequires oeeasionaloccasional human Acknowledgements interaction,interaction, isis nownow eloseclose toto bebe completely remote eontrolled.controlled. The authors' thanksthanks are duedue toto manymany WithWith thethe informationinformation andand experieneeexperience gained during the first test run at thethe colleagues at ESO, Observatoire de 3.6-metre telescope, we are a big step closer to an "Adaptive Optics User colleagues at ESO, Observatoire de 3.6-metre telescope, we are a big step closer to an "Adaptive Optics User Meudon, ONERA,ONERA, andand LASERDOTLASEADOT whowho InstrumentInstrument forfor Infrared Infrared Wavelengths"Wavelengths" which eQuldcould be offered to any visiting astronomer. With the current plans to upgrade the prototype to approximately have contributed toto thethe design andand con-eon­ astronomer. With the eurrent plans to upgrade the prototype to approximately struction of this prototype system. In 5050 subapertures,subapertures, anan adaptiveadaptive systemsystem for full eorreetion correction of a 4-metre-class struetion of this prototype system. In particular, we are thankful to Claude teleseopetelescope forfor thethe wavelengthwavelength regionregion above about 2 I-Imkm will beeomebecome available. particular, we are thankful to Claude InInthe the beginningbeginning itit will bebe aa beneh-typebench-type instrument, but in less than three years Marlot of01 Observatoire dede MeudonMeudon andand itit couldcould bebe convertedconverted toto aa lullyfully integratedintegrated system - as the "aetive"active opties"optics" is thethe MechanicalMechanieal WorkshopWorkshop atat La SillaSilla forfor alreadyalready forthefor the ND.NlT. F. MERKLE, ESO "adapting" thethe adaptive systemsystem toto thethe 3.6-metre telescope.teleseope. 12 The STST-ECF-ECF After the LaunchLaunch of HSTHST S. 01Di SEREGO ALIGHIERI,ALiGHiERi, ST-ECF

One month after thethe launchlaunch of thethe inging toto a stable "fine lock",lock", the the most months during which thethe performances Hubble Space Telescope (HST)(HST) thethe ex­ex- precise trackingtracking mode of HST. of thethe instrumentsinstruments will be calibrated on citement isis high among us at thethe Space Nevertheless, these successes are in­in- celestial targets. SV isis thethe responsibilityresponsibility Telescope European Coordinating termixedtermixed with failures failures toto acquire guide of thethe teamsteams thatthat have developed the Facilitiy (ST-ECF).(ST-ECF). We were able toto stars, which have caused considerable instrumentsinstruments and many of us will be followfollow thethe launchlaunch and thethe deployment of disruption in thethe OV schedule. c10selyclosely collaborating with thesethese teamsteams inin HST inin real-timereal-time on thethe NASA "select" On thethe positive side, all instruments instruments thethe effort of understanding thethe in-orbitin-orbit televisiontelevision channel, projected on thethe big have been turnedturned on and are performing performance of the instruments. In order screen in thethe ESO Auditorium and we according toto specifications or better, toto convey thethe resultsresults of thisthis work toto are now closely monitoring thethe activities thethe Wide Field Camera has obtained thethe thosethose European astronomers who are during thethe current Orbital Verification firstfirst images images (with(with still warm CCOs)CCDs) and directly involved with HST data, we (OV)(OV) phase (an(an engineering check-out of thethe focusfocus of thethe telescopetelescope is is improvingimproving have set up threethree Special Interest Interest HST). slowly but steadily. We are tryingtrying toto Groups, connected with thethe Wide Field With little surprise to those aware of keep the interestedinterested scientists informed informed and Planetary Camera, the Faint the complications of the HST, a number about the progress with the HST by Object Camera and the two spectro­spectro- of problems in the operation of the tele­tele- posting information from various sour­ sour- graphs. scope have emerged and are under de­de- ces on our HST bulletin board, which After SV the HST will finally start the tailed examination. For example, the can be accessed from the outside by scientific observations with the first one­one- range of orientation of the high-gain an­an- logging in intointo the captive account year cycle of programmes already allo­allo- tennae, which provide the high-speed STINFO on the ESOMCESOMCl1 Vax computer cated to the instrument teams (the so­so- data link to the ground via the relay (no password needed). We are also an­an- called Guaranteed Time Observers) and satellites, is limited to 91 % of the whole swering questions concerning HST e­e- to the GeneralObservers.General Observers. If you wish to sky by a cable harness. The effects of mailed to ESOMC 1I::STOESK::STDESK (on SPAN) apply for HST observing time during the this limitationlimitation on the efficiency of the ortoor to STOESK@OGAES051STDESK @ DGAESO51 (on Bitnet). second cycle, look forward to the telescope can be made negligible by a Our direct involvementinvolvement with HST data Announcement of Opportunity which proper scheduling of the observations. will grow in a couple of months, when will be issued by the Space Telescope Considerable efforts are also being de­de- OV will be completed and the engineers Science Institute in Baltimore around voted to achieve a reliable procedure for will hand over the telescope to scien­scien- the end of May 1990, with a proposal pointing the HST. Successful guide-star tists, so to speak, for the Science Verifi­Verifi- deadline no earlier than 15 November acquisitions have been obtained, lead- cation (SV), a phase lasting about five 1990.

PROFILE OF A KEY PROGRAMME A Wide-Angle Objective Prism Survey for Bright Quasars D.o. REIMERS, Hamburger Sternwarte, UniversitätUniversitat Hamburg, F. R. Germany

Quasars are the most luminous ob-ob­ Schmidt (HS 1700 + 6416, V = 16.1, tool to study the intervening matter with jects in the universe which - not to z = 2.72, Reimers et al., 1989). the aim to learn about large-scale struc-struc­ speak about a growing interest in under-under­ One of the reasons for the rareness of ture, evolution of galaxy halos and standing these luminous active nuclei of such objects is that pure UV excess galaxies, and chemical evolution of the galaxies themselves - can be used as surveys like the Palomar Green Survey universe. It has turned out that a spec-spec­ light sources that probe the intervening do not find QSOs with z > 2.2 and that tral resolution of 110o5 5 may be required to matter at large cosmic distances early in because of the low surface density of resolve narrow absorption-line systems. the history of the universe. However, the such objects, wide-angle multicolour or Fairly bright QSOs will therefore be re-re­ number of known QSOs, in particular at objective-prism Schmidt surveys are quired even for the VLT,VLT, and here is one high redshifts, which are sufficiently necessary. A further more practical re-re­ of the long-term goals of this Key Pro-Pro­ bright for detailed follow-up observa-observa­ quirement is the ability to process a gramme: to provide a samplesampie of high tions is extremely small. So, e.g., al-al­ larger number of Schmidt plates on a redshift QSOs for detailed absorption-absorption­ though several thousand QSOs are reasonable time scale, i. e. quick search line studies with the VLT.VLT. known at present, the only high-redshift methods are needed. A further motivation comes from the QSO sufficiently bright for the short-short­ Bright quasars (V < 17) can be used finding of J. Surdej and collaborators -­ wavelength camera of the IUE satellite, forfor multiwavelength studies of thethe cf. thethe ESO Key Programme on gravita-gravita­ and as such a prime (accepted) target quasar phenomenon itself. At sufficient-sufficient­ tionaltional lenseslenses (Surdej et al., 1989) - thatthat forfor thethe Hubble Space Telescope, was lyIy high redshifts, quasars with absorp-absorp­ thethe success rate of finding gravitational discovered only in 1988 by thethe Hamburg tiontion lineslines can be observed at high reso-reso­ lenselense effects is particularly high inin high-high­ Quasar Survey with thethe Calar Alto lutionlution (-(~0.2 0.2 A), e.g. with CASPEC, as a luminosityluminosity quasars (HLQ) with M,Mv

13 <-29. This means, e.g., that all QSOs Q 0530-379 Plate 8398R eso with z > 1.7 and V < 17 are candidate objects which can be checked on multi­ plicity with the superior angular resolu­ tion of the ND. Bright high-redshift QSOs ofter also the possibility to study the quasar EUV with HST. For z > 2.8, both He I 584 Ä and the Lya of Hell at 304 Ä and the corresponding Hel and Hell absorption "forests" are in principle observable with HST. HS 1700 + 6416 just missed the minimum redshift for Hell 304 A. Finally, it appears that existing quasar surveys are quite incomplete at the bright end. We recently found with HS J' .~ 0 +--tt/-lr--/1Hfflftt/-'------++-\I-+4lHHI c 0624 + 6902 01 = 14.2, z = 0.37) the w brightest ever optically discovered QSO o (Groote et al. 1989). This particular QSO has a strong "Iittle blue bump" - a well­ 7000 6000 5000 4500 4000 3500

known excess emission in some QSOs Wavelength (~J due to Fell and the Balmer continuum­ shifted to ~ 4000 It therefore would Ä. R 1249-131 Plate 8437R eso not have been found with pure UV-ex­ cess techniques. With the resolution of the ESO Schmidt objective prism the quasar would have been discovered easily through its Mg II emission line at 3840 Ä. Further evidence for the incom­ pleteness at the very bright end is the 1000 fact that the ratio of bright QSOs 01 < 15) detected by optical to those by other means (radio, X-ray, IRAS) is 5 : 8, ~ quite untypical for QSOs as a class. c o o In the last few years, an automated u 500 Cf) QSO search software for objective­ o Q. prism plates has been developed at Hamburg Observatory and was suc­ cessfully applied to plates taken with the ~ c w Calar Alto Schmidt (the former Hamburg o Schmidt, a slightly smaller "twin" of the 0+-----.-1-'1------1 ESO Schmidt). The plates are scanned with a POS 7000 6000 5000 4500 4000 3500 1010 G in a low-resolution mode with Wavelength [~J on-line background elimination so that ESO objective-prism spectra ofa QSO (upper, Z = 0.29) and an AGN (z = 0.01). Note that at the resolution of the ESO prism, 0111 and Hf! are separated. data are compressed to 5 % (5 Mbyte) per plate. For details of the procedure I refer to Hagen (1987) and Engels et al. (1988). With a new faster amplifier of the POS, developed by the Münster group, cept a few test fields we aim at fields not like OBs (white dwarfs with only He the scan time for a whole plate plus covered by the the multicolour QSO lines) or magnetic white dwarfs may be automated QSO search is only 4 hours. Search Key Programme (Barbieri et al., recognized al ready on the prism plates. All spectra are stored on optical disks. 1989) or other surveys - we expect 50 The first high-quality prism plates for The software has been applied to and QSOs with V < 16 (including about 20 12 fields have just arrived, and we look tested with the Calar Alto Schmidt for absorption line studies) and 400 forward to see new exciting candidate plates, in particular an 8 square-degree QSOs with V< 17 (including 100 HLQs objects. field where we have identified 23 new for a gravitational lense search). Hope­ Collaborators in this Key Programme QSOs to V = 18.8 by slit spectroscopy fully 2 or 3 QSOs with z > 2.8 suitable are the gravitational lense group headed of all candidates. Altogether, several for HST Hel and Hell line studies are by Sjur Refsdal, Hamburg, the Liege hundred new bright QSOs have been among them. A side product will be quasar and gravitational lense group (J. identified on the Northern Sky. large numbers of AGN (Z < 0.08) and Surdej and collaborators), both with in­ Since the ESO Sky Atlas is essentially emission-line galaxies, since contrary to terest in finding further bright lensed complete, the time appears ripe to use other automated surveys, we start ob­ objects, J. Wampler (ESO) who would the ESO Schmidt equipped with its ject selection on prism plates before like to see new interesting QSOs sufti­ prism (480 Älmm) for a large-scale star-galaxy separation. A further side ciently bright for high resolution spec­ spectral survey on the Southern Sky in product will be many new white dwarfs troscopy of QSO absorption lines, and combination with automated tech­ and hot subdwarfs. At the resolution of finally the stellar groups at Kiel and niques. The limit will be around B = 18. the ESO prism, WOs can be easily sepa­ München for bright WOs and 0 sub­ On 200 fields (= 5000 squ. degr.) - ex- rated from subdwarfs, and rare classes dwarfs as by-products.

14 References vey, in Proceed. Workshop on Optical Sur­Sur- ty of Hamburg. veys for QSO, Astr. Soc. Pacific Conf. SeroSer. Reimers, D., Clavel, J., Groote, D., Engels, D., Barbieri, C. et al., 1989, The Messenger 58, 2,143.2, 143. Hagen, H.-J., Naylor, T., Wamsteker, W., 22. Groote, D., Heber, U., Jordan, S.: 1989, As-As­ Hopp, U.: 1989, Astron. Astrophys. 218, Engels, D., Groote, D., Hagen, H.-J., Rei­ Rei- tron. Astrophys. 222, LL1.1. 71. mers, D.: 1988, The Hamburg Quasar Sur- Hagen, H.H.J.:J.: 1987, Doctoral thesis, Universi- Surdej, J. et al.: 1989, The MessengerMessenger55,55, 8.

PROFILE OF A KEY PROGRAMME A PhotometriePhotometric and SpeetroseopieSpectroscopic Study 01of Supernovae 01of All Types 1 2 3 2 M. TURATT0TURATTO1,, P. BOUCHETBOUCHET', , E. CACAPPELLAROPPELLARO 1,I, I.J.I. J. OANZIGERDANZIGER~,, M. OELLADELLA VALLEVALLE',, 4 2 3 5 C. FRANSSONFRANSSON~,, C. GOUIFFESGOUIFFES~,, L. LUCy3,Lucy3,P. P, MAZZAUMAZZALI~,, M. PHILUPSPHIL LIPS^

1'~sservatorioOsservatorio Astronomic0Astronomico di Padova, Italy; 2ESO,2~~~,La Silla, Chile; 3ESO,3~S0,Garehing,Garching, F.F, R. Germany; 4Stockholm4~tockholm Observatory, Sweden; 5Cerro'Cerro Tololo Inter-American Observatory, Chile

Supernovae are unpredictable events. In this framework, our Key Pro­Pro- The regular allotment of telescope For this reason, despite the fact that gramme, dedicated to the study of the time over a span of years, awarded to their interest spreads over numerous photometriephotometric and spectroscopic evolu­evolu- the Key Programme, will allow us to different fields, from stellar evolution to tion of SNe of different types, has been address different questions. the interstellar medium and to cosmolo­cosmolo- proposed and approved at ESO. The From a quick inspection of the Asiago gy, they have been observed, generally, general aim of the programme is to Supernova Catalogue (Barbon et al. with medium/small telescopes, whose accumulate regularly spaced photo­photo- 1989),1989), it appears that the average rate of schedules are flexible enough to ensure metry, particularly for constructing discovery in the last years is of about prompt observation of new objects. bolometric light curves, and spectros­spectros- 20 SNe per year. Of these, about 6 are Therefore, the observations have been copy of SNe from their earliest closer than 40 Mpc (H = 50 km/s Mpc) limited to the first months after outburst, announcement. At the same time, late­late- and reachable from La Silla. Whatever and even in this period hardly on a regu­regu- time spectra of already known SNe will their type, all these SNe stay above the lar basis. be secured. It will be possible to store in detection limit of EFOSC (or EMMI) for The recent experience with SN 19871987AA a large unique database a great deal of longer than 1 year in spectroscopy and has demonstrated the large interest in material for aselecteda selected samsamplepie of super­super- 2 years in photometry. We will be able, this field of research including the ESO novae. Emphasis will be put on observ­observ- therefore, to cover all phases of the opti­opti- community, and also that it is possible ing a few objects in detail rather than cal evolution for several SNe of various to carry out successfully, even within a many sparsely. types. large structure like ESO, a programme needing regular observing for periods of years. Thanks to the use of appropriate equipment and to a dense temporal coverage approved by the OPC, as­as- tronomers at ESO have been able to announce a number of firsts, such as SN 1988A the discovery of molecules and dust for­for- mation, the temporal mapping of the 56CO56Co (+(+57C~)57 CO) decay (both from the bolometric light curve and the measure­measure- ment of the CoCollII 10.52 i-!y line), the first order computation of elemental abun­abun- >­ I- dances in the envelope and the spectral V) Z characteristics of the just resolved shell U.J I­ around SN 19871987A.A. There has also been Z much success in theoretical modelling of the expanding envelope. Successful observations of a samsamplepie of SNe with modemmodern detectors at large telescopes during a pilot programme started at ESO have also demonstrated that it is possible to follow photometri­photometri- cally and spectroscopically the evolu­evolu- tion of SNe, other than the exceptionally Gloseclose SN 19871987A,A, for years (Fig. 1) and, 3700 4700 5700 6700 7700 8700 9700 at least in some fortunate cases, even WAVELENGTH Ä for decades (Turatto et al. 1989). The EFOSC spectrum of SN 1988A at about 444 days after the discovery.discovery,

15 Although spectroscopy is available for which will lead toto thethe determination of early-stage observations are mlsslngmissing several SNe lala around maximum light, light, thethe totaltotal mass of radioactiveradioactive 56CO56Co pro­pro- and an unambiguous classification is we still entirely lack bolometric lumi­ lumi- duced. Regularly spaced spectra of a thenthen impossible. impossible. However, there there are nosities and regular spectral observa­ observa- number of objects will clarify whether all about 70 SNe older than 10 years ac­ ac- tionstions beyond 150150 days. It is not clear, inin thethe documented differences are real or cessible fromfrom La Silla, whwhichich are can­ can- fact,fact, how wide among various objects due only toto thethe uneven spacing of the didates for detection. Although many are thethe differences suggested both by available information. IfIf thisthis variety rep­rep- difficulties arise when one tries toto locatelocate spectra (Branch et al. 1988) and by light resentsresents differences in in thethe envelopes of thethe very faint candidates inside inside thethe pa­pa- curves (Barbon(Barbon 1980) and how theythey cor­cor- thesethese SNe, itit isis not clear how this relatesrelates rentrent galaxy, even a small number of relaterelate with other parameters. This could toto thethe characteristics of thethe progenitor successes would constitute milestones be a problem forfor the the frequent frequent use of stars. inin thethe understanding of thethe evolution of such objects as standard candles un­ un- Beside thethe regularlyregularly spaced observa­observa- young SNR. lessless such differences can be accounted tionstions of newly discovered SNe, a special The collaboration with CTIO, with for and calibrated in a systematic way. effort will be devoted toto thethe identifica­identifica- whom important coordinated observa­ observa- For thethe lessless luminousluminous and rarerrarer Type IbI b titionon and eventual observation of "very tions have been obtained on SN 19871987A,A, SNe, thethe observational status is is at pre­pre- old" supernovae. There exists, in fact, and with thethe Asiago Observatory, forfor thethe sent even worse. Few objects have opti­opti- an observational gap between thethe latestlatest early stages of thethe SNe visible also from cal light curves, and bolometric informa­informa- stages of SNe, which can be placed at thethe northern hemisphere, should also tiontion isis completely lacking.lacking. Even thethe early about 2 years after thethe lightlight maximum, ensure both a better temporal and spec­spec- spectral evolution isis poorly known (be­(be- and the youngest SNRs, whose ages tral coverage. cause of sparse observations). Because are of the order of a few centuries. The the conditions in the envelope have not optical detection of SN 195701957 D inin MM8383 been clarified, since neither a spectros­spectros- (TurattoFuratto et al., 1989; Long et al., 1989) copic temperature nor a thermal equilib­equilib- and of SN 1885A inin M31M 31 (Fesen et al., References rium calculation have been derived, the 1989) indicatesindicates that itit isis possible to get Barbon, R.: 1980, in SNt,SNI, Proceedings of the actual mass of oxygen has not been precious information on the interrnedi­intermedi- Texas Workshop on Type Il supernovae, determined to within a factor of 10, pre­pre- ate agageses even with the presently avail­avail- ed. J.J.C.C. Wheeler (University of Texas, Au­Au- venting an accurate determination of the able instrurnentation. instrumentation. In particular, the stin), p. 16. mass range of possible progenitors and spectrum of the 30-year-old SN 195701957 D Barbon, R., Cappellaro, E., Turatto, M.: 1989, their contribution to the chemical evolu­evolu- inin M83 shows broad [0111][OIII] 4959, 5007 Astron. Astrophys. Suppt.Suppl. 81, 421. tion of galaxies. lines with asymmetric profiles and a ve­ve- Branch, D., Drucker, W., Jeffery, D.: 1988, Astron. J. 330, L 117.11 7. The heterogeneous class of Type 11II locity of the maximum emission of ap­ap- Fesen, R.A., Hamilton, A.J.S., Saken, J.J.M.:M.: SNe represent another interesting field proximately -650 km/s relative to the 1989, Astrophys.ASlfOphys. J.341,J. 341, L55. of investigation. In particular, we will try rest velocity. This could be due to the Turatto, M., Cappellaro, E., Danziger, I.J.: to understand if different shapes exist presence of dust filling the line-forming 1989, The Messenger 56, 36. also in the bolometric light curves and to region analogous to the situation found Long, K.S., Blair, W. W.P.,P., Krzeminski, W.: determine their total energy budget, in SN 19871987A.A. For this SN, unfortunately, 1989, Astrophys. J. 340, L25.

PROFILE OF A KEY PROGRAMME Optical Follow-up Identifications of Hard X-Ray1X-Rayl Soft y-Ray Sources Discovered by the "SIGMA" Telescope G. F,F. BIGNAMI, P.A. CARAVEO, S. MEREGHETTI, lstitutoIstituto Fisica Cosmica, Milano, Italy J. PAUL, A. GOLDWURM, L. VIGROUX, Service d'Astrophysique, CEA Saclay, France P. MANDROU, G. VEDRENNE, J. P. ROQUES, CERS, Toulouse, France

The aim of this programme is to The SIGMA telescope (constructed by 11005- 5-10 1o6 6 sec. pointed observations of search for the optical counterparts of two French groups at CEA/SaclayCENSaclay and the 3-axis stabilized telescope. hard X-raylsoftX-ray/soft y-ray sources (including CESR Toulouse) aboard the Soviet After the mandatory outgassing y-ray bursts and transient events) dis-dis­ GRANAT satellite represents the first period of the various SIGMA subsys-subsys­ covered by the SIGMA telescope (suc-(suc­ breakthrough in one of the last unex-unex­ tems, more than two months of in-flight cessfully launched on December 1, plored wavelength regions in as-as­ operations were required both to com-com­ 1989), also exploiting the soft X-ray data tronomy. Launched on December 1, plete the telescope adjustment (a quite of the all sky survey to be performed 1989, it consists of a gamma camera/ difficult task, taking into account the 131 by the ROSAT satellite (launched(Iaunched on coded mask telescope system (see photomultiplier tubes of the gamma May 31, 1990). Fig. I)1) separated by 2.5 m, with imaging camera, the on-board calibration sour-sour­ It will be the first time that coordina-coordina­ capability yielding a source localization ces and the active shielding device), and tion between on-going high-energy accuracy of 2' within a field of view of to evaluate the background along the space missions, such as SIGMA and 4034c; 3 x 40 4c; 7 and a sensitivity inin thethe orbit. This is now stabilized on a rather ROSAT, and ground-based telescopes millicrabmilliCrab region. The energy range goes constant value of 440 counts/sec, which isis implementedimplemented on a programmed long-long­ fromfrom 35 keV toto 1.3 MeV, and operations, compares favourably with thethe one com-com­ termterm basis. planned for twotwo years, will be based on puted on thethe ground of 320 counts/sec,

16 inging aa rapidrapid coordinationcoordination withwith ground·ground- basedbased oplicaloptical observations.observations. ItIt isis worthworth nolingnoting thatthat tMthe rectangutarrectangular telescopetelescope fleldfield ofof viewview fealuresfeatures aa centralcentral area,area, inin whichwhich thethe telescopetelescope isis atat itsits maximum,maximum, surroundedsurrounded byby aa widewide fieldfield ofof decreas­decreas- inging sensitivitysensitivity (the(the half·sensitivityhalf-sensitivity boundaryboundary isis aa 1096x1O? 6 x 119411 ? 4 rectangle)rectangle) withinwithin whichwhich sourcessources cancan stillstill bebe posi­posi- tionedtioned withinwithin aa fewfew arcminutes.arcminutes. InInparallel parallelto tothe the SIGMASlGMA higherhigherenergy energy observations,observations, thethe well~knownwell-known ROSATROSAT missionmission willwill workwork inin thethe softsoft (.1-2(.I -2 keV)keV) X-rayX-ray domain,domain, performingperformingfirst first aasky sky sur­sur- veyvey andand thenthen aa sequeneesequence ofof pointedpointed observations.observations. TheTheproposers proposersof of thisthis ESOESO KeyKey ProgrammeProgramme havehave organizedorganized aa eol­col- laborationlaborationbetween betweenthe the twotwo missionsmissionsfor for exploilingexploiting thethe ROSATROSAT surveysurvey daladata onon thethe basisbasis ofof thethe SIGMASlGMA results.results. ThisThis shouldshould resultresult inin anan improvementimprovement ofof bothboth sourcesource positioningpositioning andand knowledgeknowledge ofof spectralspectral Shape,shape, renderingrendering muehmuch moremore intereslinginteresting andand meaningrulmeaningful thethe searchsearch FiglX8rlgure I;I: The1neSIGMA SIUIVIHcoded coaeamask. maSK. AA patternpattern ofor 4949)( x 53SY absorbingaosoro~ngelementselements (1.5 (7.3an cm tungsten)rungsrenl forfor thethe opticaJoptical counterpart.counterpart.Based Basedon on thethe isis arrangedarranged inin aa URAURA (Uniformly(Uniformly RedundantRedundant Amry),Array), eacheach elementelementis is 9.49.4x x 9.49.4 mm.mm. proposer'sproposer's experieneeexperiencein in opticaloptical studiesstudies ofof ylX-rayyiX-ray sources,sources, thethe additionaddition ofof lhethe ROSATROSAT datadata willwill bebe erucialcrucial 10to thethe successsuccess ofof !histhis profectproject especiallyespecially farfor thethe consideringconsideringthe the eurrentcurrent highhigh levellevel ofof s0­so- themthem havehave aJreadyalready beenbeen observed.observed. searchsearch farfor anan opticaloptical idefltiflcationidentification ofof larlar activity.activity. AtAt thethe endend ofof thisthis evaluationevaluation ThanksThanks toto thethe dimensiondimension ofof thethe fullyfully newfynewly discovereddiscovered sourcessources whichwhich isis thethe period,period, severalseveral GrabCrab nebulanebula observa·observa- codedcoded fl8k:ffield ofof view,view, severalseveral burstsbursts willwill mostmost challenging,challenging, aJbeitalbeit thethe polenliallypotentially lionstions werewere performedperformed toto assessassess thethe in·in- bebe observedobserved throughthrough thethe imagingimaging codedcoded mostmost rewarding,rewarding, partpart ofof thethe programme.programme. orbitorbit capabilitiescapabilities ofof thethe telescope.telescope. 80thBoth masl

Report on the First ESOICTIOESO/CTIO Workshop: "Bulges of Galaxies"

The first ESO/CTIO Workshop was There were eleven invited and about will be published later this year by ESO. held on January 16-19, 1990, in La thirty shorter, contributed papers. A It was a pleasure to work together Serena, Chile. The scientific sessions poster session was also provided. The with our colleagues from CTlOCTIO and it took up 3 days with 2 afternoons re-re­ meeting was attended by about 90 sci-sci­ was good to hear many positive com-com­ served for visits to the La Silla and To-To­ entists from 5 continents. About 30, ments from the participants. 1010lolo observatories. The theme of the mainly young participants, were partially I hope that there will be many more workshop was "Bulges of Galaxies" supported by the conference funds such joint meetings held in Chile and and included all aspects of bulge re-re­ allowing them to attend and to present that they may all be as stimulating as search, both Galactic and in external contributions. this one. galaxies. The proceedings are being edited and H. E. SCHWARZ, ESO

News About the ESO Exhibition

The travelling ESO Exhibition has a setting up its exhibition at the University Free University of Brussels, Astrophysi-Astrophysi­ busy time this summer. Last year it was from July 17 to 29. There will be public cal Institute, Pleinlaan 2, B-1180 decided to duplicate most of the exhibi­exhibi- access; more details can be obtained Brussels, Belgium. tion items, so that it can be shown in from the organizer, Dr. Chris Sterken, ESO was pleased to acacceptcept an invita- two places at ononce.ce. This has paid off and both exhibitions are now booked out through most of 1991. ESO was present, together with its sisisterster organizations CERN, ESA and EMBL, at the "Europa Ricerca" exhibi­ exhibi- tion in Rome, Italy on May 31 -June 10. This major presentation of large Euro­ Euro- RICERCA pean science and technology projects was organized by the Italian Chairman­Chairman- ELHEKA ship of Eureka in connection with the VIIIVlll Eureka Minister Conference. ELA COOPEIL\ZIO\E It you visit Geneva inin Switzerland this summer, don't miss a tour through the '1'[(:\01 jOCIC\ new CERN Microcosmos, just installed installed ELIH)PEA on the CERN grounds near Meyrin, out­out- side the city. In addition to learninglearning about the smallest particles, you will see beautiful pictures of galaxies and stars inin one area of thethe Microcosmos build­build- ing.ing. Here thethe ESO Exhibition is installed until thethe end of August. It was inaugu­ inaugu- ratedrated on May 28 by thethe Directors Gener­Gener- al of CERN and ESO, Professors Carlo Rubbia and Harry van der Laan. The "Free University" of Brussels inin Belgium will be host toto thethe American Association of Variable Star Observers From the opening ceremony of thethe Eureka Minister Conference and the exhibition Europa (AAVSO)(AAVSO) thisthis summer. This is thethe first Ricerca - (Ieft(left toto right)right) thethe Italian ltalian Minister for for Universities and TechnologicalTechnological Research, A. timetime that that this this venerable American or­ or- Ruberti, CEC Vice-PresidentVice-President F. M. Pandolfi, ESA OirectorDirector General R. LüstLiist and ESO OirectorDirector ganization meets outside its home General H. vanvan der Laan. Participating in thethe ceremonyceremony were thethe Italianltalian President, Francesco country, let on another continent. InIn rec­rec- Cossiga, ministers and high representativesrepresentatives fromfrom thethe Eureka member countries and thethe EEC, ognition of thisthis importantimportant event, ESO isis directors general fromfrom CERN, EMBL, ESA and ESO as weilwell as delegates toto thethe conference.conference. 18 tion to present its exhibition at the Council of Europe in Strasbourg, 12th European Regional Astronomy Meeting of France, from September 26 to October 12. During this period, both the Council the lAUIAU of Europe and the European Parliament The preparations for this meeting (see the announcement in MessengerMessenger59,59, will meet in this impressive building, p. 25) are proceeding weilwell and the organizers expect a large influx of Euro­ Euro- situated in a park area near the centre of pean astronomers from all geographical areas of the continent. The meeting the Alsatian capital. This exhibition will will start in Davos Kongresszentrum (Switzerland) in the early afternoon of not be open to the public, but it is ex­ex- Monday, October 8, 1990 and end around noon on Thursday, October 11, in pected that it will be visited by about order to facilitate travel on these days. 4000 delegates, media representatives All prospective participants who have not already done so, are urged to and staff. contact soonest the Chairman of the Local Organizing Committee at the Next, ESO will show its face in the following address: second-Iargestsecond-largest city of Portugal, Porto. Professor Dr. U.U.W.W. Steinlin The exhibition opens late September in Astronomisches Institutlnstitut der UniversitätUniversitat Basel the old steel-and-glass market hall Venusstrasse 7 whwhichich has recently been transformed CH-4102 Binningen into a perfect exhibition site. ESO's Switzerland presence in Portugal is particularly time­time- or by email: EARN:[email protected];EARN: [email protected]; Iyly in view of the current efforts to estab­estab- SPAN: CHGATE::YOGI::SCHWENGELER. lish closer contacts between Portu­ Portu- guese astronomy and ESO. In mid­mid- Correspondence concerning the scientific organization should be directed November, the exhibition will move on to the Chairman of the Scientific Organizing Committee: to the capital, Lisboa, where it is ex­ ex- Professor Dr. L. Woltjer pected to stay until the end of the cur­cur- Observatoire de Haute-Provence rent year. Further information may be F-04870 St-Michel l'ObservatoireI'observatoire obtained from Prof. Teresa Lago, Grupo France de Matematica Aplicada, Faculdade de Calendar: Ciencias, Universidade do Porto, Rue July 15 Registration form to Dr. Steinlin das Taipas 135, P-4000 Porto. Hotel reservation to Davos Tourist Office Future exhibition sites include cities in Aug. 15 Abstracts of papers to Dr. Woltjer Austria, Norway and Spain, as weilwell as in Fees must be paid to meeting account South America; announcements of Sept. 15 Third Circular with Final Programme dates and sites will be made in the next Oct. 8 Meeting opens in Davos: abstract book available issues of the Messenger.Messenger,

New Videos from ESO European Group of Astronomical

Three new video films have recently Librarians (EGAL) become available from ESO: • "Window to the Universe": A film In July 1988 lAUIAU Colloquium 110,110, en­en- description of each library. The main aim about ESO made by the BBC. titled "Library and Information lnformation Services is to foster informal cooperation and 24 min. Available in English, French, in Astronomy" was held in Washington communication between librarians in all German and Italian. D. C. This was attended by 120 people European countries, with a special em­em- • "The First NTTNlT Images": A presenta­presenta- from 26 different countries, including phasis on strengthening and impraving improving tion of the first images from the NTT,NlT, several European librarians, most of links with our Eastern Eurapean European col­col- obtained during the commissioning whom met each other for the first time. leagues. The possibility of also acting as phase; made by the ESO Informationlnformation Inspired by the stimulating talks and dis­dis- apressurea pressure group, for instance when Service. 9 min. Only available in En­En- cussions, and the desire to transmit the problems with publishers or suppliers glish. "spirit of Washington" to other col­col- occur, is not excluded. • "The NTT Inauguration": A summary leagues who were not able to attend, Initially about 70 librarians were con­con- of the main events and speeches the idea of EGAL was born during the tacted and replies were received fram from during the inauguration of the NTTNTT' on closing stages of the meeting. about 40. The first EGAL Bulletin, No. 0, Frebruary 6, 1990, in Garching and at On our return Suzanne Laloe (Institut a trial number, was mailed in May 1989 La Silla. 24 min. Only available in En­En- d'Astrophysique, Paris) and myself dis­dis- to all the librarians on our original mail­mail- glish. tributed areporta report of the meeting together ing list. This brought in some more re­re- The videos are available on VHS, S­S- with a letter proposing the formation of plies and we compiled the first version VHS, MMI1II and Betacam on two an informal group of European librarians of the Directory. This was distributed, cassettes; one with "Window to the Uni­Uni- working in astronomical observatories together with EGAL Bulletin No. 1, in verse", while "First Images" and "NTT and institutes. The response was en­ en- October 1989, again to all the persons Inauguration" are on a common cas­ cas- couraging and we decided to go ahead on our original list. It is hoped that EGAL sette. The price per cassette is 70.- DM. with our basic idea of distributing a Bulletin will become a forum for news, Orders should be placed with the ESO newsletter 2 or 3 times a year and pub­pub- opinions, descriptions of libraries and Informationlnformation Service (address on last lishing a directory of names and ad­ad- routines, queries for help and informa­ informa- page). Please note that the delivery time dresses, telephone, telex, telefax num­ num- tion. Many observatory and institute li­ li- will be about 4 weeks. bers and e-mail addresses, plus abriefa brief braries are relatively small and isolated. 19 Often there is only one person in charge of the library, and their feeling of isola­isola- 1 ANNOUNCEMENT tion can perhaps be alleviated by the knowledge that there are several other The 4th ESO-CERN Symposium on people in a similar situation whom one can contact by telephone or computer. "Cosmology, Astronomy and Fundamental It must be stressed that the success of Physics" EGAL will depend on the willingness of and the 15th Texas Symposium on the participating librarians to involve and the 15th Texas Symposium on themselves actively via the Bulletin, by "Relativistic Astrophysics" supplying items of news and information will be combined into a joint Texas/ESO-CERN Symposium to be held at the which could be of interest to other mem­mem- will be combined into a joint TexasIESO-CERN Symposium to be held at the bers. Conference Centre in Brighton (U. K.), 16-21 December 1990. The first two numbers of the Bulletin The Scientific Organizing Committee (co-chaired by M. J. Rees and G. Setti) were produced and distributed with the has outlined the following programme: help of the Max Planck Institute for As-As­ trophysics, Garehing.Garching. We are extremely Morning plenary lectures on: grateful to ESO for its kind support in Early Universe; Quantum Cosmorogy, Cosmology, High-Energy Physics - ratestlatest results; Nucleosynthesis; Galaxy Formation and High-z Objects; Large­ taking over the production and mailing results; Nucleosynthesis; Galaxy Formation and High-z Objects; Large- Scale Structure; Dark Matter; X-ray and y-ray Astronomy; Pulsars; Gravi­ from No. 2, March 1990 onwards. Scale Structure; Dark Matter; X-ray and y-ray Astronomy; Pulsars; Gravi- tational Lensing; Background Radiation; Solar Oscillations; Neutrinos We apologize to any Iibrarianlibrarian reading tational Lensing; Background Radiation; Solar Oscillations; Neutrinos and Underground Physics; Gravitation Theory. this who was not contacted and did not and Underground Physics; Gravitation Theory. know about EGAL. SoSomeme names were Afternoon mini-symposia on: deleted from our original mailing list be­be- Astrophysics of Neutron Stars and Black Holes (Organizer - R. D. Bland­Bland- cause of failure to respond, but we will ford) welcome any librarian who is willing to Underground Physics (Co-organizers - B. Sadoulet and P. F. Smith) cooperate and share his/herhislher experience Large-Scale Structure and Galaxy Formation (Organizer - G. Efstathiou) and problems. There is no charge; so far The registration fee will be f: 75 (f: 25 for students). A first circular with a we only exist through the medium of the The registration fee will be f 75 (f 25 for students). A first circular with a registration form has been circulated to institutes on the ESO mailing list. Bulletin and the Directory. Sometime in registration form has been circulated to institutes on the ESO mailing list. the future it may be possible to organize Information may be obtained from: some kind of meeting, but there are no firm plans as yet. Any European as­ as- Professor L. Mestel Chairman, Local Organizing Committee tronomical librarian who is not yet a Chairman, Local Organizing Committee member of EGAL and would like to be­be- Texas/ESO-CERNTexasIESO-CERN Symposium Astronomy Centre come one is invited to contact me at the Astronomy Centre address given below. Division of Physics and Astronomy University of Sussex A. FISHBURN Astrobibliothek,Astrobib/iothek, MPI Astrophysik Falmer, Brighton BN1BNl 9QH Karl-Schwarzschild-Str. 1 ENGLAND 0-8046 GarehingGarching bei MünchenMiinchen

The New Look of the ESO Headquarters

00Do you see something special on this photo? Yes, indeed, now the ESO Headquarters in GarehingGarching has a new fifth floor! Photo made on a beautiful Bavarian spring day by ESO photographer H.-H. Heyer on Kodak High-Speed Infrared Film through an orange filter (f/8.5,(fl8.5, 1/25011250 sec). 20 lAUIAU WG on Photogra­Photogra- phy To Meet at ESO Vacancies INFRARED ASTRONOMER The lAUIAU Working Group on Photogra­Photogra- Education: University degree in Astronomy or Physics, preferably a doctorate. phy (of lAUIAU Commission 9) will meet at Experience and knowledge: A solid background in observational infrared the ESO Headquarters on October 29 astronomy and a good working knowledge of infrared instrumentation. and 30, 1990. Very good knowledge of English and a working knowledge of Spanish. The topics will include: manufacture Assignment: As an international staff member in the La Silla Astronomy Department, and behaviour of astronomical emul­ emul- the successful applicant will be expected to spend about half of his/her time doing sions, photographic techniques (sen­ (sen- original research and half doing support duties. The support duties include being Head of the IR Operations Group, introducing visiting astronomers to the use of IR instrumen­instrumen- sitometry, hypersensitization, calibra­ calibra- tation, and supervising the programmes of IR service observing. As Head of the IR tion, conservation), applications (mea­ (mea- Operations Group, he/she will supervise changeover routines of instrumentation, surements and reduction, numerical maintenance of instruments and detectors, development programmes in hardware and techniques) and photography/CCOphotography1CCD in­in- software, and, in general, will be responsible for monitoring the quality of the IR facilities teraction. Although CCOsCCDs have taken offered by the Observatory. over in many areas, photography is still Facilities: The observing facilities on La Silla comprise 14 telescopes including the of great importance for certain as­ as- SEST 15-m submillimetre antenna and the new 3.5-m ND.NTT. Infrared facilities are tronomical applications at many obser­obser- available at 4 telescopes and include IR photometers, an intermediate-dispersion vatories, in particular in large-field sur­ sur- spectrograph (IRSPEG),(IRSPEC), and an imaging array camera (IRAG).(IRAC). The research computing facilities on La Silla comprise a HP 1000 system with fl)lIfull vey-type work. image-processing capabilities (IHAP), a VAX 11/750 and several SUN workstations for The scientific programme is being es­es- image processing (MIDAS). tablished by J.-L. Heudier and J. General information: Close to 20 astronomers, including staff members, fellows and Schumann; they can be reached at Ob­Ob- students, work on La Silla. The research projects currently pursued by the astronomical servatoire de la CoteCBte d'Azur,dlAzur, B.P.B. P. 139, staff at La Silla include low mass star formation (Herbig-Haro objects, molecular F-06003 Nice Cedex, France (EARN­(EARN- outflows, jets), OH/IR stars, symbiotic stars and proto-planetary nebulae, coronal email: WGAP@FRONI51).WGAP@FRON151). The local activity in late-type stars, supernovae, chemistry of molecular c1ouds,clouds, formation of arrangements are made by the ESO In­In- massive stars and starburst activitiy, dynamics of galaxies, active nuclei, QSOs and formation Service (address on the last gravitational lensing, and observational cosmology. Duty station: Astronomical Observatory, La Silla (600 km north of Santiago, Chile). page). page). Starting date: As soon as possible. Applications should be submitted to ESO Personnel Services at ESO-Garching before July 31,1990.31, 1990.

FELLOWSHIP AT LA SILLASlLLA STOP PRESS (June 6,6,1990)1990) A position is available at La Silla for a post-doctoral fellow with an interest in observational astronomy. Experience with IR spectroscopy, or optical photometry will be an advantage. ESO fellowships are granted for aperiod a period of one year, normally At Last, We Know renewed for a second year and exceptionally renewed for a third and final year. The successful applicant will be expected to spend not more than 5050%% of his/her Where La Silla Is! time in support-related activities and the rest of the time doing scientific research. Applicants normally should have a doctorate awarded in recent years. Applications Recent geodetic VLBIVLBl observations, should be submitted to ESO not later than July 31,1990.31, 1990. Applicants will be notified by the first involving South America, using September 1990. The ESO Fellowship Application Form should be used and be the SEST telescope on La Silla, have accompanied by a list of publications. In addition, three letters of recommendation successfully produced an exceedingly should be obtained from persons familiar with the scientific work of the applicant. accurate position for the La Silla tele­tele- These letters should reach ESO not later than July 31, 1990. scope. The observations performed by Enquiries, requests for application forms and applications should be addressed to: the OnsalaiSESTOnsala/SEST group in collaboration European Southern Observatory with the NASA Crustal OynamicsDynamics project Fellowship Programme using SEST in VLBI VLBl mode with tele­tele- Karl-Schwarzschild-StraßeKarl-Schwarzschild-StraOe 2 D-8046 GARCHING b. Munchen scopes at Westford, Mass., Mojavi, D-8046 GARCHING b. München Federal Republic of Germany Calif., and Onsala, Sweden, give a posi­posi- tion solution for SEST as: X = 1,838,239.55 m Y = -5,258,700.06 m New ESO Preprints Z = -3,100,588.47 m in a geocentric coordinate system de­ de- (March-May 1990) 699. E. Gosset and J.-M. Vreux: On the Pos­Pos- fined by the major VLBIVLBl telescopes. The sible Biperiodicity of WR 40. Astronomy distances between these telescopes Scientific Preprints and Astrophysics. have been determined with formal un­un- 697. L. Greggio and A. Renzini: Clues on the 700. L. Pasquini, E. Brocato and R. Pallavi­Pallavi- certainties, depending on the baseline Hot Star Content and the UV Output of cini: Chromospheric Activity of Evolved length, between 6 and 23 mm, e.e.g.g. the Elliptical Galaxies. The Astrophysical Late-type Stars. distance from the Onsala 20-m tele­tele- Journal. 701. S. Cristiani et al.: Observations of Vari­Vari- scope to SEST is: 698. Ph. Prugniel and F. Combes: Dynamical able Quasar Candidates. Monthly Friction in Pairs of Elliptical Galaxies. Notices of the Royal Astronomical 80­ So- 10,459,732,492.4 mm (±(+ 23.1 mm). Ph. Prugniel and E. Davoust: Tidal Dis­Dis- ciety. Note that this is only a first result and tortions in Pairs of Early-type Galaxies. 702. A.V.A. V. Sweigart, L. Greggio and A. Ren­Ren- further processing, involving the full ob­ob- Contributions to lAUIAU Colloquium 124 zini: The Development of the Red-Giant serving network of 8 telescopes, is in "Paired and Interacting Galaxies", Tus­Tus- Branch: 11.II. Astrophysical Properties. progress. R. BOOTH, Onsala caloosa, December 4-7, 1989. The Astrophysical Journal. 21 703. E. Gosset et al.: Analysis of the light Light Factors AffectingAllecting On-Axis Operation. Pa­Pa- Astronomical Images with Adaptive Op­ Op- Variations of the Wolf-Rayet Star per presented at the SPlESPIE ConferenceConlerence tics. To be published in the SPIESPlE Pro-Pro­ WR 16. AstronomyAsfronomy and AstrophysicsAstrophysies 1236 on "Advaneed"Advanced Technology OpticalOptieal ceedings No. 1236. Supp/.Suppl. SeroSer. Telescopes IV"IV" on February 12-16 inin 20. P. Kern et ai.:al.: Adaptive Optics Prototype 704. M. Morris and Bo Reipurth: The Optical TuesonTucson AZ, USA. System for Inlrared Infrared Astronomy. I: Sys-Sys­ Form 01of the Bipolar Preplanetary Nebu-Nebu­ 16. J.J.M. M. Beckers: The VLT Interferometer. tem Descriplion. Description. To be published in thethe la IRAS 09371 +1212. Pub/.Publ. Astron. Ill.111. FactorsFaetors Affecting Wide Field-ol-ViewField-of-View Spie Proceedings No. 1271. Soc.SOC.Paeifie.Pacific. Operation. Paper presented at the SPlESPIE 21. F. Merkle et al.: Adaptive Opties Optics Proto-Proto­ ConlerenceConference 1236 on "Advaneed"Advanced Tech-lech­ type System forlor JRIR Astronomy.AstrOrlQmy. 11:II: First nology OptiealOptical Telescopes IV" on Febru-Febru­ Observing Results. To be published in ary 12-16 in Tucson AZ,AZ., USA. the SPlESPIE Proceedings No. 1271. Technical Preprints Technieal Preprints 17. J.M. J. M. Beckers: IheThe VLT Interferometer. 22. P. Dierickx et al.: ESO VLT II:11: Optical 13. A.F.M. Moorwood and B. Delabre: In­In- IV. The UtililyUtility of01 Partial Adaptive Optics. SpecificationsSpecilications and Performance of01 Large fraredfrarad Spectrometer/lmager forfor the ESO Paper presented at the SPlESPIE ConlerenceConference Optics. To be published in SPIESPlE Pro­Pro- VL1.VLT. To appear in Proceedings 01of SPlESPIE 1236 on "Advancad"Advanced lechnologyTechnology OpticalOptieal ceedings No. 1237. Conference 1235 "Instrumentation in As-As­ Telescopes IV" on February 12-112-16, 6,19901990 23. P. Dierickx et al.: The 8.2 MetreMelre Primary tronomy VII". in Tucsonlucson AZ, USA. Mirrors of01 theIhe VLT. To be published in the 14. J.M. Beckers et al.: The VLT Inter-Inter­ 18. M. Faueherre Faucherre etel al.: Michelson Versus SPlESPIE Proceedings No. 1271. ferometer.ferometer. I. Proposed Implementation. Fizeau Type Beam Combination: Is 24. R.N. Wilson, F. Franza and L. Noethe:Noelhe: Paper presented atatthe the SPIESPlE Conference There a Diflerence?Difference? To be pubiishedpublished in ActiveAetive Optics IV: Set-up and Perfor-Perfor­ 1236 on "Advaneed"Advanced Technology OptiealOptical the SPIESPlE Proceedings vol. 1237 on "Am-"Am­ mance of the OpticsOpties of theIhe ESO New lelescopesTelescopes IV" on February 12-16,12-1 6,19901990 plitude and Intensity SpatiaJSpatial Interferome­Interferome- Technology Telescope (NT)(NTT) in the Ob-Ob· in lucsonTucson AZ, USA. try", ed. J.J.B. B. Breckinridge. servatory. SubmittedSubmilted forfor publication in 15. J.J.M. M. Beckers: The VLT Interferometer. 11.II. 19. F. Merkle et al.: First Diffraction-LimitedDiffraction-Umited Journal of Modern Optics.Opties.

STAFF MOVEMENTS Professor J. H. Oort at 90 Arrivals ~ur'o~e:Europe: BALLESTER, Pascal (F), ScienceScienee ApplicationsAppIicalions PrograrnmerProgrammer BERGER, Christian (0),(D), StudentSludent BRYNNEL, Joar (S), Electronics EngineerlTechnicianEngineernechnician COMIN, Mauro (I), System Programmer GEHRING, Georg (0),(D), StudentStudenl GOUIFFES, Christian (F), Fellow GROESSL, Martin (A),(A). VLTVLT Project Engineer HES, RoiandRoland (NL), Student HILL, Susan (GB), Archive Operator HUBIN, Norbert (F), OptiealOptical Engineer KOCH, Franz (0),(D), StrueturalStructural Analysis Engineer NIEUWENKAMP, Christine (NL), Adm. Asst. Purchasing PIOTTO,PIOlTO, Giampaolo (I), Associate ZEILINGER, Werner (A), Fellow

Chile: DELLA VALLE, Massimo (I), Fellow EKMAN, Sture (S), Eleetro-MechanicalElectro-Mechanical Engineer HEINAUT-ROUELLE,HEINAUT-ROUELLE, M.-C. (B), Associate WILD, WollgangWolfgang (0),(D), Fellow (SEST)(SESl) Departures Europe: Jan Hendrik Oort,Dort, aneone of the founding fathers(athers of ESO, celebratedceiebrated his 90th birthdaybirlhday GOSSET, Eric (B), Fellow GOSSET, Erie (B), Fellow on April 28, 1990. He was the President of the ESO Council tromfrom 1964 to 1965 and POSTEMA, Hans (NL), MechaniealMechanical some of his many services to ESO and the world-wide astronomicalastronomica/ community Design Engineer WENOORFF,WENDORFF, ChanesCharles (DK), Associate have been outlined in the articlesartic/es by Adriaan Blaauw in the recent Messenger issues. WOLWOLTJER,TJER, Lodewijk (NL), Associate Professor DortOort continues to take an interest in ESO affairs and was delighted to10 see the first resultsresutrs from{rom the New Technology Telescope.Telescape. Chile: The photo shows Professor DortOort f1ankedflanked by Professors Blaauw (right)(fight) and Wo/tjerWoltjer BAUOET,BAUDET, laicLoic (F), OptiealOptical TechnicianTechnieian (left)(Ieft) and Professor van der Laan at the reception held in Leiden in honour of the GOUIFFES, Christian (F), Associate famous Dutch astronomer on this festive oCC8sionoccasion (Photo: Loek Zuyderduin).Zuyderduinj, 22 ESO'S EARLY HISTORY, 11953-1975953 - 1 975 VII. The Late 1960's: Structural Changes, First Scientific Activities and Some Soul-Soul­ Searching; the Journal AA& & A* A. BLAAUW, Kapteyn Laboratory, Groningen, the Netherlands

"La construction et I'installation du grand telescope ------sont I'objet de serieuses preoccupations de lala part de la delegation --- - -".

From a letter of the French Council delegates toto thethe President of Council, June 15, 1969.

Introduction per January 1, 1968; and Blaauw Scien-Scien­ Recommendations Concerning the Ex-Ex­ tific Director on 50%50 % time basis per ploitation of the Observatory" [I].[1]. As it The late 1960's were years of tran- tran­ February 1, 1968. reflected what at that time was ex-ex­ sition. With the dedication of La Silla in The new set-up functioned till Heck-Heck­ pected from ESO, let me mention some March 1969, ESO's first phase of con-con­ mann's retirement as Director General of its contents. structions had been concluded. Realiza-Realiza­ at which moment he was succeeded by It started by saying that "Whereas the tion of the Schmidt and the 3.6-m tele-tele­ the author. Ramberg continued as role of the observatory as an astronomi-astronomi­ scopes would be the main goals for the Technical Director (he would retire per caleal institute in its own right ------should next years, besides the Observatory's December 31, 1971). The post of Scien-Scien­ be of great importance,importanee, the facilitiesfaeilities of taking up its functions as a research tific Director was suppressed per Janu-Janu­ the observatory should particularlypartieularly be institute. The transition was accom-accom­ ary 1, 1970. Heckmann continued for a available to serve the national interests panied by a change in the structure of limited period as consultant in connec-connec­ of the member states." ToTothis this end, the management of the Organization tion with the work on the Schmidt and there should be a staff of permanent and and by the creation of a Scientific Pro-Pro­ 3.6-m telescopes. Some other major semi-permanentsemi-permanent members - to be en-en­ grammes Committee. While the latter, appointments made about this time, gaged at the ESO establishments - and as one of its assignments, reflected on, connected with instrumental develop-develop­ the facilities should be frequently used and suggested, directives for ESO's ments and administrative affairs will be by visiting astronomers from the ESO long-range development beyond the Ini­Ini- mentioned later. countries. Besides the research by indi­indi- tial Programme of the Convention, the Meanwhile, Bengt E. Westerlund had vidual staff members and visiting as­ as- Organization also underwent some per June 1, 1969 taken up the position tronomers, the observatory might con­con- thorough - and sobering - soul-search­soul-search- of Director for Chile (based on Council's duct "general programmes ------to pro-pro­ ing. These developments, together with decision of June 1968) after having been vide doeumentsdocuments of fundamental signifi­signifi- abriefa brief account on the first scientific associated with Steward Observatory in eaneecance but not neeessarilynecessarily requiring im­im- activities and the role ESO played in the Tucson, Arizona, bringing to ESO his mediate analysis, such as, for instanee,instance, creation of the journal Astronomy and thorough acquaintance with the South­South- a sky-atlas, astrolabe programmes, sys­sys- AstrophysicsAstrophysies will be dealt with in the ern Sky gathered during earlier associa­associa- tematietematic observations in SeleetedSelected Areas, present article. bontion with Mount Stromlo Observatory in ete.etc. " and these "are the responsibility of Australia. Andre Muller, after almost six the CouneilCouncil who, upon the reeommen­recommen- Changes in the Directorate yearsvears of buildingbuildinq upu~ ESO inin Chile, re­re- dation of the Seientifie Scientific Programmes turned to Europe~urop-ewhere he joined the Committee, may charge a staff member At the November 1966 Council meet­meet- Committee, may charge a staff member Office of the Director in Bergedorf per or, possibly, another astronomer with ing,ing, Otto Heckmann reminded Council October 15, 1969 for the new task of the supervision of such a programme."programme. " members that it was the present a organizing the rapidly growing Visiting "Semi-permanent staff members management's task "- --- - to construct Astronomers ProgrammeProgramme... As we have --- normally employed for about 3 the Observatory, not to work scientifi­ scientifi- seen inin article IV, observational activity years in Chile ------should be weilwell cally --- - -", and that his appointment as on La Silla had started at the end of aequaintedacquainted with the instruments and are Director per November 1, 1962 had 1966 with the 1-m telescope. It now to be charged with the instruction of the been for a term of five years, thus end­end- to be eharged with the instruetion of the grew rapidly. visiting astronomers in order to ensure ing per November 1967; adecisiona decision efficient use of the observatory's would soon have to be taken on his effieient use of the observatory's faeilities.facilities. ------they [also] may be future role.role. The Council meeting of June Earliest Scientific Activities and ehargedcharged with thethe responsibility forfor the the 1967 ensured Heckmann's continued the Creation of the SPC exeeutionexecution of the "general programmes". supervision of construction activities by About one year after thethe ratificationratification of --- At any time,time, therethere should be pre­pre- extending his appointment tilltill thethe end of thethe ESO Convention, in its December sent inin Chile and at the disposal of thethe 1969, and responsibility for thethe develop­develop- 1964 meeting, Council appointed a Director, for each major ESO telescope ment of scientific activity was assigned Oireetor, for eaeh major ESO teleseope small advisory committee forfor preparing a permanent or a semi-permanent staff to myself in part-time association with a a a discussion on the way thethe Observato­Observato- member weil well aequaintedacquainted with thatthat tele­tele- thethe ESO Directorate. These moves were ryry should operate: on thethe size and role of seope.scope. "With" With regard toto semsemi-permanenti-permanent formalized by Council decisions of De­ De- permanent and semi-permanent staff, staff the document stated that "in"in order cember 1967 at which also Ramberg's thatthat of visiting astronomers, thethe alloca­alloca- that ESO may attract qualified as- position was redefined: Heckmann be­be- that ESO may attraet qualified as­ tiontion of observing time,time, etc. The group, tronomerstronomers ------itit isis neeessarynecessary that theythey came Director General until December consisting of A. Blaauw (Chairman),(Chairman), possess the guarantee of eontinuation continuation 31, 1969; Ramberg Technical Director E. Geyer,Gever. A. van Hoof, P. Lacroute and of theirtheir positions inin thethe home countries B. Lindblad,~indblad, met at Bergedorf on upon their return from Chile ------eon­con- 'Previous* Previous articlesarticles inin thisthis seseriesries appearedappeared inin thethe May 6, 19651965 and submitted toto Council tinuationtinuation of pension rights and ------so­so- Messenger Nos.NOS. 5454 toto 59.59. a document "Considerations"Considerations and eialcial seeurity security benefits. It isis of great im-im- 23 By way of introducOOnintroduction toto ourour descripliondescription 01of lhethe earlyearly obsetvationalobservationalacrMries activities on La SilIa,Silla, we show lhethe ObsefvatoryObservatory under Ihethe southemsouthern sky, as seenseen by thethe Chi1eanChilean artistartist Nemesio Anlhunesz.Anthunesz. The painting waswas made at thethe requestrequest of thethe SwedishSwedish NaturalNatural ScienceScience Research CoonciI-Council - ESO being oneone oftheof the many projects thlsthis CounciICouncilsupports - aOOand itit decoratesdecorates thisthis CounciI'sCouncil's W8flOOf-GrenWenner-GrenGentra Centre Headquarters inin Stockho1m.Stockholm. InIn 1970, when h8he made thethe painting, Anthunesz waswas DirsetexDirector of thethe Museo Naciona/Nacional de Bellas AltesArtes inin Santiago. InIn lhethe artist's impressionimpression WBwe recognizarecognize lhethe g9tlef81general layoutlayout of thethe ObsetvatoryObservatoryas seen from the south, with thethe $chmidt-Schmidt-TelescopeTslescope bIli/dingbuilding inin the foregroundforeground aOOand thethe clustercluster of intsrmediale-sizeintermediate-size lelescopetelescope domes - and even thethe ENTEL Communications System ra/ayrelay mast - fartherfarther down. (Compara(Compare thethe photograph on page 31 of Ihethe previous article.) We also recognize, to the leftleft above thethe Observatory, the conspicuousconspicuous constellation of the SouthemSouthern Cross wlth,with, starting fromfrom Itsits extreme lowerlower right star Alpha Crucls,Crucis, in c/ock-wiseclock-wise order the stars Beta, Gamma, Delta aOOand EpSilonEpsilon Crucis. Natural/y,Naturally, as Itit isis Joca/edlocated at declination -60",-604 Inin rsaUtyreality thethe Sou/hemSouthern Cross can be seen {romfrom La Silla only inin southerly dlrectiondirection - bu/but /Jevernever mindmind... . . The au/hO'author isis indebted toto Dr. M. O.0. OIlOSSOIJ,Ottosson, Council member fO'for Sweden, who kindly made thethe photograph of the painting avai/ableavailable farfor the Messenger. portance that the respective govem­ govern- InIn several respects, the arrangements sisting of AA. Blaauw, R. Cayre!Cayrel and O.0. ments of the member stafesstates adopt a suggested were modifl6dmodified in actual prac­prac- Heckmann) for making a more definite cooperative attitude towards this tice. Not Council, botbut thelhe ESO OirectOfDirector proposaJproposal for the task and conslitutionconstitution of problem. "~ would be in chBfgecharge of theIhe execulionexecution of the proposed ScientificSeientific Programmes Visiting astronomers were supposed general programmes; short stays of vis­vis- Committee. The Iowlow priority which these to stay in Chile forfOf' periods of two iting astronomers became the rule maUersmatters still had at that time is reflected months to one year. The advisory group rathet"rather than the exception; applications by the fact that only in October 1966 the also proposed that Council establish were not first scrutinized by national group formulated its advice 121[2] forfOf' sub­sub- two kinds of fellowships: those for commitees; special fellowships forfOf' dis­dis- mission to the December 1966 Council young students, and those fOf'for distin­distin- tinguished astronomers would not be in meeting. This ledlad to samesome revisions of guished scientists invited 10to do research Of'derorder during the first decade; and June 1967 {31,[3], following the Council at an ESO establishment. FOf'For Ihethe alloca­alloca- guarantee forfOf' semi-permanent staff's meeting earlierear1ier that month. At that meet·meet- tion of observing time the advisory com·com- continuation of their employment in the ing, Council decided to establish a Sei­Sci- mittee suggested that applications by homeharne country has seldom been granted. entific Programmes Committee, tota be visiting astronomers were to be submit­submit- selected and appointed at the next tedled first to10 national committees toto be Council meeting. Meanwhile, thethe advi-advi· created for this purpose, who then created for this purpose, who then The Scientific Programmes Com-Cam­ sory group dealt with thethe allocations for would pass on the applications with would pass on the applications with mittee (SPC) the 11-m-m telescope.telescope. The December 1967 their advice to a Scientific Programmes Council meeting thenthen appointed the CommiUeeCommittee - SPC -to- to be created by the In its meeting of June 1965, Council SPC with B. StromgrenStrömgren (Denmark) as Council. Proposals were added for thelhe agreed with the suggestions of thethe ad-ad­ Chairman, and thethe members J. Delhaye constitution and thethe tasktask description of visory committee, and in December (France), E. Holmberg (Sweden), P. this SPC. 1965 it appointed a working group (con- Swings (Belgium), G. Traving (Germany), 24 member in Chile from May 1968, after November 1966 (which also gave two having been employed by ESO in useful tables with the optical properties Marseilles from January 1968 for work of the first ESO telescopes and spectro­spectro- on the RV Cass spectrograph. L. Prevot graphs). For those who attended it is of of Marseilles Observatory had been en­en- interest to recall the quite unusual gaged in the GPO programme in South weather conditions prevailing at the Africa, as described in article 11.II. In 1969 start of the Colloquium: a sudden, heavy Cassegrain and Coude spectrographic glazed frost causing breakdown of pow­pow- work was carried out in alternation. As er lines and telephone connections, and reported earlier, the 61-cm61 -cm Bochum and thus for a while isolation of Roden Ob­Ob- the 50-cm Danish telescopes came in servatory and unheated lodging for regular operation in the course of 1969; sosomeme of the participantsparticipants...... for their programmes I refer to the lists in A spectroscopic counterpart to the the ESO Annual Reports. Roden Colloquium was the ESO Collo­Collo- By the end of 1969, the astronomical quium on Spectroscopy, held at Nice staff in Chile consisted of the members Observatory on June 3-5, 1969. We are mentioned already: Westerlund, Dossin, not aware of a comprehensive report; Schuster and Maurice, to whom had contributions were published separate­ separate- been added in the course of 1969 A. Iy,ly, for instance one by A. B. Underhill on Ardeberg of Lund, from May 15, 1969, Early-Early-TypeType Stars in ESO Bulletin No. 8, and J.J.J. J. Rickard, formerly of the Califor­Califor- June 1971. The Grand Pr/smPrism Objectif (GPO) nia Institute of Technology, from Octo­Octo- After having served in South Africa in the ber 1, 1969. context of site testing, the GPO was installed The Allocation of Observing Time on La Silla where it resumed its work in the For allocating the observing time for middle of 1968. The optical principle accord­accord- The First Cooperants ing to which the instrument operates has 1968, the ESO Directorate ca calledlied a been described in artielearticle IV. The photograph An interesting addition to the staff in meeting of the applicants, in its office, shows the twin tubes of which the instrument Chile were French "cooperants". By on November 23, 1967 [7]. Inviteeslnvitees were consists: the lettleft one carrying in front the agreement with the French Ministry of A. Ardeberg (Lund), A. Behr (Göttingen),(Gottingen), specially designed objectiveobiective prism, the right Foreign Affairs, in the context of French M. de Vries (Roden), E. Geyer (Bonn) one serving for precise guiding during ob­ob- service to underdeveloped countries und U. Haug (Tübingen).(Tubingen). The meeting serving. Once installed at La Silla the GPO (specifically for Chile), young French­ French- acquainted the Directorate with the re­re- continued its work on the Magellanic Clouds, men, preferably astronomy students, search interests in the member states, but now under much better atmospheric con­con- were allowed to substitute their military and made the applicants mutually ditions than in South Africa. From ESO Historical Photographs Archives. service for work on La Silla. For this acquainted with their projects. Such service they were proposed by ESO to presentation of research proposals in the Ministry, upon recommendation by the circle of fellow applicants was soon studied in 1967 early-type stars in the French National Committee for As-As­ abandoned, however, when their southern clusters and associations and tronomy. The first ones to enjoy this number increased. carried out a test programme for a new duty were Jacques Colin from Besan­Besan- The SPC took over in the course of infrared photometer, and guest obser­ obser-

Meetings of the Scientific Programmes Committee,COImmittee, the Observing Programmes Committee and the Scientific Policy Committee* 1968-1974

SCIENTIFIC PROGRAMMES COMMITIEECOMMllTEE (SPC) Chairman: B.5. StrömgrenStromgren No. Date PlaGePlace 1 1968 May 2 Bergedorf 2 1968 October 1717 Bergedorf 3 1969 May 6 Copenhagen 4 1969 November 10 Marseilles 5 1970 April 29 Bonn 6 1970 November 11I1 Liege 7 1971 March 9 Geneva 8 19711971June18June 18 Paris 9 1971 November 23 Roden

OBSERVING PROGRAMMES COMMITIEECOMMITTEE (OPC) SCIENTIFIC POLICY COMMITIEECOMMITTEE (SPC) Chairman: B. StrömgrenStromgren No. Date PlaGePlace Chairman No. Date PlaGePlace 10 19721972June13June 13 Bergedorf P. Swings 1 1972 April 25 Copenhagen 11 1972 December 15 Heidelberg P. Ledoux 2 1972 October 10 Bergedorf 12 19731973May24May 24 Bergedorf P. Ledoux 3 1973 March 28 Paris 13 19731973 December 1111 Bergedorf P. Ledoux 4 1973 September 14 Copenhagen 14 1974 June 17-18 Bergedorf Bergedori P. Ledoux 5 1973 November 7 Paris . 15 1974 December 2-3 Obs. Haute-Provence P. Ledoux 6 19741974JuneJune18 18 Bergedorf 88'' 1974 September 3 Trieste 9 1974 December 4 Bergedorf

,* 8yBy Council decision 01of June 9-10, 1971 the Sc. Progr. Comm. split into the Obs. Progr. Comm. and the Sc. Pol. Comm.; membership was appointed in the Cou meeting 01of Nov. 30/Dec.3O/Dec. 1, 1971. 1' In numbering the meetings 01of the SPC, the number 7 was erroneously skipped.

25 May 1967. The ESO photometerphotomeier for lhethe 1-mI-m te/escope,telescope, builtbuill at81 Roden The 1-mI-m PhotometricPhotometrie TeleseopeTelescope Observatory, is mounledmounted at this telescope by Andre Muller, left, and After having been housed in a provisional dome on La Silla slncesince the Martien de Vries of Roden Observatory. The 1-m1-m telescope,telescope. Ihethe first end of 1966.1966, the telescope resumed its work in the permanent dome one in regular operation on La Silla, at Ihatthat time was still housed in its in the fall of 1968. It is shown nerehere after fhethe move.move, equipped with the provisional dome and had ear/ierearlier been used with a simpler.simpler, borrowed ESO Photometer and with Jan Doomenbal,Doornenbal, ESO's Chief mechanic in photometer. Ihethe background. During the first years, the telescope was mainlymainfy PholographPhotograph from a slide by Ihethe authOf.author. used for the sfudystudy of sfarsstars in the MagellanieMagellanic Clouds detecteddetecled by means of Ihethe GPO, and for individuafindividual Slars,stars, Slarstar cluslersclusters endand stellar associalionsassociations in our Ga/axy.Galaxy. From ESO Hls/oricalHistorical Photographs Archives.

allocation of telescope time, it also submitted these to CouneilCouncil in letters of shouldn't ESO take advantage of, and might suggest long-range research pro­pro- the SPC chairman 01of November 15 and possibly support financially,finaneially, eapabilitiescapabilities jects and extensions of ESO's observing 20, 1968, for diseussiondiscussion in the Council for suehsuch werkwork at institutesinstitutes in the ESO facilities [9] beyond the "Initial Pro-Pro~ meeting 01of December 3 and 4 [11].[Ill. We countries? gramme" of the Convention. review here these proposals and the Stromgren'sStrömgren's leiter letter 01of November 15.15, In their seeond second meeting, on GetoberOctober reactionsreaetions in Couneil.Council. 1968, presented proposals forlor new, 17, 1968, the SPC took up the thread of Strömgren'sStromgren's letter of November 20, powerful telescopes;teleseopes; these had been early Council deliberations of November diseusseddiscussed firstlirst by Council in the Oe~De- supported meanwhile by the Instrumen­Instrumen- 1966, in whiehwhich CouneilCouncil had touchedtouehed on eembercember 1968 meeting, emphasized that tation Committee on November 5 and 6 the broadening of the ESO member­member- the Headquarters in Santiago should be and eoneerned:concerned: ship, on extension of itsits instrumenta­ instrumenta- weilwell equipped with measuring facilitiesfaeilities - a photometrie photometric telescope. telescope, intermedi­ intermedi- tion, and on the possible creation, for visiting astronomers and resident ate in size between the 1-m and 3.6-m somewhere in Europe, of an ESO Centre staff,staf!, especially fer for the evaluation of telescopes,teleseopes. IOrfor instance with an aper-aper­ for the development of measuring in-in­ photographiephotographic plates.plates, but that such ture 01of 2.0-2.5 m. struments and for promoting seientificscientific equipment should be developed prefer­prefer- - a Schmidt tefescope telescope eonsiderably considerably contacts between astronomers of the ably at an ESO Centre in Europe, in larger than the ESO Schmidt at that time member states. Aeferenee Reference was also collaboration with both institutes in the under eonstruetion,construction, forlor instance one made to the promotion 01of Laboratory member states and commercial firms, with aperture 2 m and focalfocallength length about Astrophysies,Astrophysics, a new branch 01 of as­as- and this Centre should then also be­be- 6m.6 m. trophysiestrophysics that rapidly gained attention eomecome a place for evaluation 01of observa­observa- - an astrometrieastrometric telescope comparable in the mid-1960's [10].[lo]. The SPC now tional data and a scientificseientifie meeting to the one recenllyrecently acquired by the US formulated more preeiseprecise proposals and ground. As to Laboratory Astrophysics,Astrophysies. NavalObservatory.Naval Observatory. 27 The 1.52-m TelescapeTelescope equipped with the Cassegrain ~Chilicass""Chilicass" The 1.52-m Telescope, although designed primarilyprlmarily for spectros­spectros- spectrograph, borrowed from Marseilles Observatory. In the copiccopie observations, was also sometimes used fortor direct photogra­photogra- background, right, ESO's Chief-mechanieChief-mechanic Jan DoomenbalDoornenbal talking to phy, especially in the early stage of optiealoptical tests. It11 is shown here an (yet) unidentified person. In the early years, most of the observing equipped with the Zeiss camera. time with the spectrograph was devoted to thelhe determination of From ESO HistoricalHistorioal Photographs Archives,Archives. radial velocities and spectral types of stars in the Magellanic Clouds that had been detected by means of the GPO observations in SauthSouth Africa. From ESO HistoricalHistorieal Photographs Archives.

The Proposed New Telescopes limiting/imiting magnitudes in work with the - Big SehmidtSchmidt telescopeteleseope For the photometriephotometric teleseopetelescope the let­let- ESO 3.6-m reflectorrefleetor - ~- - sufficienllysufficiently far of 2 m aperture ...... $ 6,240,000.­6,240,000.- ter mentioned current research prob-prob­ for the ESO I-ml-m SehmidtSchmidt Telescope 10to - AstrometricAstrometrie telescope lemslems including: "Whoiesale "Wholesale photometry becomebeeome inadequate as a eompanioncompanion in-in­ of 1.5 m aperture ...... $ 3,200,000.-3,200,000.­ in the Magel/anieMagellanic C/oudsClouds of stars down strumentstn/ment for survey work. ---" Ae­Re- all of these including the building and the main sequenee;sequence; photometry of faint search problems considered by the SPC dome. variable stars like/ike those of the Groning­Groning- included general survey work on faint The total amounted to . $12,460,000.- en-Palomar $urvey;Survey; photometry in varl­vari- galaxies demanded by the expected For eomparison:comparison: the total estimate 01of ous globularg/obular clusters and in the direc­ direc- flowf10w of diseoveriesdiscoveries of radio sourees,sources, and the 3.6-m telescope projeetproject as it oeeursoccurs tions of the ga/acticgalactic center and centralcenlral many research programmes on galaeticgalactic in an estimate of late 1969 eompiledcompiled by bulge.bu/ge. - - - It would be unfortunate if strueture.structure. "-"----- what members of the RambergAamberg (to whiehwhich we shall refer later) work on problems of the type mentioned SPC had in mind in considering the amounted to. . . . . $$10,700,000.-.10,700,000.-. shou/dshould have to be postponed until the possibilities of a big Schmidt Telescope In the diseussionsdiscussions at the DeeemberDecember time when the 3.6-m telescopeteleseope is avai/­avail- was an aperlure aperture of approximately 2 m 1968 and later Council meetings, the able. - - - it would certainly b8be desir­desir- and a focallengthfocal length of about 6 m.m." " proposition of an ESO Centre inin Europe able to work on the problems just men· men- The proposed astrometrie astrometric telescope forlor development of Instrumentationinstrumentation and tioned with an intermediate-s/ze intermediate-size tele-tele­ was to aim at trigonometrictrigonometrie parallaxes for the promotion of laboratoryLaboratory As­As- scope - --- - with an aperture of 2-2.5 m down to magnitudes 17 or 18, and at trophysicstrophysies struck a responsive ehord chord ------the SPC favors the Cassegrain proper motions of high aeeuraeyaccuracy for the because the wish for suehsuch a eentrecentre had type refleetorreflector with Ritehey-ChretienRitchey-Chretien op-op­ study of spacespaee motions out to distances been expressed earlier inin Couneil.Council. We ties,tics, with an effeetive effective aperlure aperture ratio otof at least 500 parsec. shall later eomecome baekback to this. around 1 :8.:8. ----~ - -" Highest priority was to be given to the The proposals for additional tele­ tele- With regard to the Big SehmidtSchmidt Tele­Tele- photometriephotometric teleseope,telescope, and to studies scopes were discussed at some length scopeseope (the name used in Strömgren'sStromgren's forfar the design 01of the Big Schmidt. by CouneilCouncil inin its meeting of DeeemberDecember letter) it stated: ''-"- --- - it can be foreseen The above proposals ware were aeeom­accom- 1968. Soon after this, however, CouneilCouncil that the development of image amplifi­amplifi- panied by the following cost estimates lost interest, for it became more and eaUoncation as weilwell as photoelectricphotoelectrie spectrum drawn up by Aamberg.Ramberg. more elearclear that the ESO Directorate scanning with large numbers of - PhotometriePhotometric telescopeteleseope would have their hands fullfuH with the channe/s,channels, will make it poss/blepossible to push of 2-2.5 m ...... $ 3,020,000.- realization of the 3.6-rn3.6-m Telescope. Even 28 la Convention n'autorise I'introduction de ces instruments --- - -. La Convention n'interdit cependant pas I'introduction de ces instruments -- -.-. 1/I1 peut notamment etre8tre fait appel a cette fin a la notion de "programme supplemen- taire - - -".no The Working Group (referring to itself as Working Group for reviewing Pro­ Pro- grarnme,gramme, Administration Proeedures Procedures and StattStaff Problems of the ESO Organi­Organi- zation) met on September 11, 1969 at CERN, Geneva [13]. The choice of this loeationlocation had undoubtedly to do with the fact that Funke and Alline both were members of the CERN Council. But in a way it also was symbolic: in his com­com- ments on the ESO Administration Alline had on several occasions referred to CERN procedures as an example. In­ In- vited for the meeting were also, for the ESO Direetorate,Directorate, Heckmann, Ramberg and the Manager Bloemkolk. Main basis for the discussions was, The Coude Spectrographspectrograph after the definition of the Working For observations requiring high spectroscopic resolution the 1.52-m telescope is used in combination with the Coude spectrograph of which the upperupperpartpart is shown in this photograph. Group's task, an extensive doeument document It is mounted in fixed position below the observing floor of the telescope; the star fightlight prepared by the French delegation: collected by the telescope is directed into the spectrograph by means of a set of mirrors of "Memorandum destine EIa la diseussiondiscussion which the position adjusts itself during the motion of the telescope in such a way that the beam entre MM. Funke, Scheidemann et enters the instrument in constant direction. Work with the Coude spectrograph started in the Alline, en vue de la redaction du rapport middle of 1969 and was concerned mainly with the study of interstellar fineslines and the demande par le president du Conseil de determination of the abundances of elements in the atmospheres of the stars. I'ESO lors de la 12eme session de Con­Con- From ESO Historical Photographs Archives. seil EIa Santiago, le 22 mars 1969" [14]. The French Memo dealt successively with the questions raised earlier: changes in the "Convention-size" of the worse: concern about this realization Council discussions it was elear clear that it teleseopes;telescopes; possible ways to speed up soon overshadowed the optimistic should serutinize scrutinize many aspects of the the work on the 3.6-m telescope; the views of the SPC about ESO's growth, functioning of the ESO Administration. structure of the ESO Management in and ESO was to undergo a short but These were to inelude:include: a confrontation Europe and Chile and the danger of too sobering period of soul-searching. We of current activities with the aims as much dispersion in the latter, suggest­suggest- do note, though, that the project of the defined in the Convention, with special ing reduetionreduction of the "intermediate" sta­ sta- Danish 1.5-m national telescope, reference to such matters as the nation­nation- tions La Serena and Pelfcano Pelicano between realized later, would meet to a certain al teleseopestelescopes and the new proposals by Santiago and La Silla; and the organiza­organiza- extent the desire for the proposed the SPC; the financial implications of tion and presentation of financial and photometric telescope. suehsuch extensions; and eertaincertain aspeetsaspects of personnel matters. the functioning of the administrative management. Soul-Searching in the Late 1960's The Report of the Working Group In a letter of June 15, 1969 to the In article VI, when describing develop­develop- President of the Council (Bannier), The report of the Working Group was ments around the introduction of the Alline, on behalf of the FrenehFrench delega­delega- dealt with by CouneilCouncil at its meeting of national telescopes, I mentioned the tion, elaborated more speeifically, specifically, and December 15 and 16, 1969 [15]. The concern, sineesince late 1968, about the laeklack critieally,critically, on these problems [12]: "-"---­- Group arranged its advice into four sec­sec- of progress in the eompletion completion of the La eonstructionconstruction et I'installation du grand tions: The ESO Programme and the Schmidt and large telescopes. Soon telescope - - - sont I'objet de Convention; Budget Procedures; The signals of discontent on these and some serieuses preoccupations de la part de 3.6-m Teleseope; Telescope; and Certain Other other points grew louder and the Coun­Coun- la delegation fram;aise.franqaise. - - - La delega­delega- Questions. To the first, the Group ob­ob- cil Meeting of March 1969 in Santiago tion demande --- que les provisions served that departures from the Con­Con- appointed a Working Group to advise budgetaires - --- - prennent pour objectif vention with regard to specifications of Council, under the Chairmanship of d'achever dans les meilleurs delais la the instruments so far had been "more G.G.W.W. Funke (former President of the realisation du programme scientifique from the letter than [from] the spirit of Council), and with the members K.K.F.F. derinidefini lors de la signature de la Conven­Conven- the Convention" and had not involved SeheidemannScheidemann (President of the Finance tion [et}[et] d'effectuer des economies sur any appreciable rise in costs [16]. As to Committee) and A. Alline. Alline had just les chapitres non directement lies a cet the question, whiehwhich projects to consider beeomebecome the French government dele­ dele- objectif --- - -. L'installation et le fonc­fonc- as belonging to the regular programme, gate on Council and was the one who tionnement d'instruments nationaux it recognized the oceurrenceoccurrence of border­border- most strongly voiced feelings of dis­dis- --- n'est pas sans poser a cet egard line cases and it referred to CERN's satisfaction. The Working Group's task d'importants et delicats problemes. example of realizing a bubble chamber was not strictly defined, but from the ------Ni dans son esprit ni dans sa lettre not foreseen originally as part of the

29 The 61-cm Bochum Telescope,Telescope, installedinstalled inin SoptemberSeptember 1968, and thethe firstfirst of thethe -national"national telescopes~telescopes" on l..1iILa Silla. Financed by Bochum UniversityandUniversity and thethe DeutscheDeutsche Forschungsgemeinschaft,Forschungsgemeinschaff, itit offered Bochum observers thethe outstanding observingobserving conditions o(of l..1iILa Si/laSilla wllereas,whereas, (orfor thelogisticthe logistic (acilitiesfacilities offeredoffered by ESO, ESO obsefversobservers received 30%30 % o(of thethe observingobserving time.time. The teJescope,telescope, manufactured by BoIlerBoller & Chivens,Chivens, waswas equipped with aa photo--eJectricphoto-electric photometer made stat tfJethe central workshop o(of GöttingenGottingen University.

regularregular programme and including including in in itsits concerning possible reduction of the the ESO countries could work together regularregular programme preliminary work for dispersion of the facilities inin Chile, and itit and also, in collaboration, new instru­instru- a storing ringring project pertaining to the suggested that Council reconsider itsits ments could be developed ---".---~. To Supplementary Programme. saJarysalary policy to make staft staff positions some exlenl, extent, Ihese these wishes would be The Working Group recommended to more attractive than they had been so satisfied by Ihethe TP-Division created ear­ear- Council "8"a certain preparation (or for the far. Iyly inin the 1970's. continuous expansion", so as to enable Judging from the minutes, the De.­De- With regard 10to financial and personnetpersonnel itit to consider carefully whether new pro­pro- cember 1969 Council Meeting tooklook note maUers,matters, dissatisfaction among some jects shouJdshould be includedincluded inin the regular of the repartreport withou1 without extensive discus­discus- Council delegales delegates stemmed mostly programme. With regard to national te-te­ sion. The meeting had a crowded agen­agen- fromfrom!wo two causes: a lack of stability in the Iescopes,lescopes, tOOthe Group recognized that da because of the succession in thetha budget requirements, and lacklack of trans-trans­ they "can"can become a worthy addition toto General Directorate, and this did includeinclude parency in the documentation fer for R·Fi- the ESO instruments·,instruments", yet they "--­"- - - as itsits principal item importanl important repartsreports nance Committee and Council. The lal­lat- would normally be aflocatedallocated to the sup­sup- concerning the 3.6-m Telescope Pro}ectProject ter was not difficuttdifficult to understand in plementary programme provision of which we will encounter later. Yet,Vet, there view of the fact that the ESO Manage­Manage- --- the Convention or they would be are several items in the memo and the ment had to setsei up an organization of wholly paid by ihethe country concemed concerned Report which have distinclly distinctly left theirthair unprecedented nature and size in as-aso ------·unless" unless Council specifically illCOf·incor- mark on later developments in ESO and tronomy, whereas most of the members porated thamthem inin the regular programme. thereforeIherefore are worth pointing out here. of Council and FC were accustomed to With regard to budgetary procedures First of all, this soul-searching had a streamlined procedures in well-estab-well-estab­ the Group recommended the adoption sobering effect on the over-optimisticover-optimislic lished organizations. of a procedure similar to thatthat used by suggestions made by the SPC forfar ex-ex­ For improving the situation, as a CERNGERN (see below). For the 3.6-m tele-tele· tensions of the ESO facilities.facilities. However, naturalnalural example Council tendedtended to look scopescope. project the Group recommended Council appeared to10 remain receplivereceptive to atproceduresal procedures established atal CERN with thethe preparation of a comprehensive theIhe idea of theIhe creation of01 an ESO its tenten years longer experience (CERN status report and a detailed time- and Centre in Europe, where "the most was createdcrealed in 1952). An important re-re­ cost schedule. Finally, the Group re-re­ sophisticated equipment for(or evaluation sult was the introduction, in the early frainedfrained fromfrom submittingsubmiUing any proposal should be located, astronomers from(rom 1970's, of thethe so-called Bannier proce- 30 The Copenhagen 50-ern50-cm Te/eseope,Telescope, the second of the "national The ESO 50-ern50-cm Te/eseopeTelescope shortly after its installation in late 1971. telescopes", shortly after it had been installed in its permanent dome The telescope is a duplicate of the Copenhagen 50-cm telescope in the middle of the year 1971. When it arrived on La Silla early in and was, like the latter, manufactured at Copenhagen. It was 1969 it was first mounted in the dome that had served earlier for the acquired by ESO in the context of developments for the control ESO 1-mI-m telescope. The photograph shows it with the Copenhagen system of the 3.6-m Telescope so that these could first be tried out in 4-channel photometer designed for photometry in the so-ca so-calledlied actual practice on a small instrument. Initially, as in the above StrömgrenStromgren narrow-band system. photograph, it was equipped with a one-channel photometer. Like the two 50-cm telescopes, their domes also are twins.

dure adopted by CERN for budget plan­plan- tion framfrom the middle of 1970; it will figure (Continued on page 34) ning; I expect to return to this later when in the list of Council meetings in a later reviewing financial and personnel de­de- article. CentrefoldCentrefold velopments.velo~ments.In order to avoid misunder­misunder- standings it should also be recorded Giant clouds of moleeulesmolecules and infrared ESO and the Creation of the Jour­Jour- here, that the report of the Working sources are invariably linked to star-forming that the Of the Working nal AstronomyandAstrophysicsAstronomyandAstrophysics regions. GraupGroup explicitely stated that "- -­- - The complex star-forming region NGC It seems appropriate to devote in the Management [essentially consisting of It seems appropriate to devote in the 3576 is located near the plane of our galaxy, the Manager J. H. Bloemkolk and his present context a few paragraphs to the at a distance of about 3.6 kpc.kpc, ~~~~~i~~~~Associated staft}staff] has accomplished its work in com­com- role ESO played in the year 1968 in the with this nebula lies a giantqiant molecu/armolecular cloud mendable fashion --- - -".-" creation of the journal A &&AA which since of mass ~- 10lo55 MG!'Mg. A cluster of 5 infrared then has become one of the leading sources have been reported. Approximately astronomical journals, and still has an seven early-type (young) stars would be Creation of Committee administrative link to ESO. Its creation, needed to ionize the entire observed region, ofCouncilof Council too, was one of the steps in the process some 10 arcminutes in extent. Spectacular ares arcs and streaming motions Finally, we note that at the March of Europeanization of scientific activity. can be seen in this colour-composite, made 1969 Council Meeting in Santiago the The ciose close tie between the Journal and from three black-and-white Schmidt plates, suggestion was made, by Alline, that ESO, reported below, has led to the secured by OavidDavid Block at La Silla earlier this ESO follow CERN's example by having incorporation of the documentation re­re- year.year. The blue (IIla-J)(Illa-J) and red (lIIa-F)(Illa-F) plates a "Committee of Council" for the pur­ pur- lated to the Chairmanship of the Board herewere hypersensitized in nitrogen and firmingforming pose of discussing in an informal of Directors of the JournaloverJournal over the first gas and exposed for 60 min and 120 min, manner, in between Council meetings ten years of its existence, into the ESO respectively through GG 385 and GG 495 fil­fil- and with restricted participation, those Historical Archives. Accordingly, refer­ refer- ters. The green (103a-0)(103a-D) plate was exposed items whichwh ich might give rise to con­con- ence is made to these archives [18]; for 60 min with a GG 495 filter to approximate the V ("visual'')("visual':, waveband. traversiestroversies between the Council delega­delega- helpful has also been an earlier account The composite was made by Claus Mad­Mad- tions mutually, or with the Directorate ­- by the author on the creation of the sen and reveals important temperature gra­gra- and thus pave the way for smooth Journal [19].[I 91. dations, from the red to the ionized pink-pink­ Council proceedings. A Committee of On April 8, 1968 some leading as­ as- white central area. Council was established at the De­De- tranomerstronomers fram from Belgium, Denmark, D. BLOCK, ESO and University of cember 1969 meeting [17][I 71 and did func- France, the Federal Republic of Ger- Witwatersrand, South Africa 31

many and the Netherlands met at been a time-consuming and somewhat [1][I]FHA Ooc.Doc. ScAct-1.ScAct-1 . Leiden to prepare a possible merging of complicated affair. An alternative solu­solu- [2] FHA Ooc.Doc. ScAct-2. some of the principal astranomicalastronomical jour-jour­ tion was therefore preferred: making use [3] FHA Coc. ScAct-3. [4] Für a short biography of B. Strömgren nals that appeared in Europe [20]. The of the legal status of ESO, whose aims [4] For a short biography of B. Stromgren see, for instance, the obituary by M. meeting had been convened by S. R. as a joint European astronomical pro­pro- meeting had been convened by S.R. RudkjöbingRudkjobing in QuarlerlyQuarterly Journal R.A. R.A.S.S. Pottasch of the Kapteyn Laboratory gramme ran parallel to those of the Vol. 29, p. 282,1988.282, 1988. who, together with A. Reiz of Copenha­Copenha- Journal. The matter met support by the [5] See the report by Blaauw in ESO Bulletin gen Observatory and J.-L. Steinberg of ESO Council in July 1968, so that steps No. 4 of July 1968. Meudon Observatory had been the first could be taken to prepare the necessary [6] See Minutes Cou Meeting, June 1970, to explore attitudes with regard to a legal documents. These found final ap­ap- p.41.p. 41. possible merger; Pottasch and Stein­Stein- proval and confirmation at the De­De- [7] See FHA OocsDocs ScAct-4 and 5. berg were closely connected with edito­edito- cember 1968 Council Meeting [22]. They [8] FHA Ooc.Doc. ScAct-6. [9] See FHA Ooc.Doc. ScAct-3 of June 1967. rial work for a journal in their countries. were: [10][lo] Minutes 7th Cou Meeting, p. 29ft.29ff. The idea found general support and nininene - a statement concerning the creation [11][I11 Strömgren'sStromgren's letter of Nov. 15 with months later, per January 1, 1969, the of the Journal and the relation of its accompanying Cou Letter 00/2426/68 first issue of the new journal appeared. board of Directors to ESO; of Ramberg, and Strömgren'sStromgren's letter of The merging journals were: Annales - a formal agreement between ESO Nov. 20 with accompanying Cou Letter d'Astrophysique (founded in 1938), Bul­Bul- and the Board of Directors; 00/2464/68 by Manager Bloemkolk, letin Astronomique (1884),(1 884), Journal des - the contract between ESO and the both in FHA Cou and FC Ooc'sDoc's 1.1.1./1.1.1./ Observateurs (1915),(191 5), Zeitschrift fürfur As-As­ publisher, Springer Verlag; 1.2.1.,1.2.1., Circular Letters. trophysik (1930),(1930), and Bulletin of the and accordingly Council authorized the [12][I21 Letter marked 3137/6931 37/69 in file FHA 1.1.1/1.1.l/ 1.2.1. Astronomical Institutes of the Nether­ Nether- Director General of ESO to sign the con­con- [13] FHA Ooc.Doc. Cou-2, 2283/69. lands (1921), to which was added later tract just mentioned. lands (1921), to which was added later [14] In FHA, attached to the Report of the the Scandinavian Arkiv för for Astronomi The basic idea was, that ESO would Working Group referred to under refer­refer- (1948). First editors of the new journal make its administrative and legal ser­ ser- ence [14].; an English translation was were S. R. Pottasch and J.-L. Steinberg. vices available to the Board of the Jour­Jour- made at the request of Funke according The related series A & A Supplements nal but would carry no financial obliga­obliga- to FHA 1.11/1.21,1.11/1.21, Cou-2 2321/69. appeared one year later, per January 1, tion or responsibility. Apart from making [15] FHA Ooc.Doc. Cou-2 3304/69. 1970 under the editorship of L. L. E. use of ESO's services, the Board would [16] We note that in the W. Group's report Braes of Leiden, who was succeeded in have an entirely independent status ex­ex- the GPO is not considered as one of the three middle-size telescopes of the 1971 by B. Hauck of Lausanne. The cluding influence from ESO side on its Convention, contrary to the decision ta­ta- Monthly Notices of the Royal Astronom-Astronom­ scientific policy. As a trait-d'union be­ be- ken by the ESO Committee in July 1960 ical Society refrained framfrom merging, by tween ESO and the Board, the author, at as reported in article IV. decision of the Council of the Society on that time Scientific Director of ESO, be­be- [17]1171 See, for instance, FHA Ooc.Doc. Cou-2 October 13,196713, 1967 [21]. came a member of the Board of Direc­Direc- 3309/69. How did ESO come in? The April 1968 tors - and was, in fact, chosen as its [18] EHA-1.EHA-I.C.7.;C. 7.; not yet subclassified in Oe­De- meeting had resolved that the affairs of Chairman. cember 1989. the Journal should be supervised by a Henceforth, European astranomers astronomers [19][I91 In Europhysics News, Bull. of the Eur. Board of Directors consisting of as­ as- would turn to the new Journal for the Phys. SOG.,Soc., Vol. 6, No. 12, Oec.Dec. 1975, p.3-5.p. 3-5. tronomers and representatives of spon­spon- publication of their work - including that [20] AAreport report on this meeting by S.S.R.R. soring national organizations. This based on observations at La Silla. Pottasch is in the section Earliest De­De- Board should be the autonomous owner velopments of the Archives. of the Journal, including the title, with a References and Notes [21] The Archives contain the relevant corre­corre- private publisher acting as agent for the spondence of O.D.H.H. Sadler and F. Abbreviations used: Board. However, in order to enter into a Graham Smith with J. H. Oort and S. R. EHA = ESO Historical Archives (see The contract with the publishing agent as Pottasch of October 1967, and the re­ re- contract with the publishing agent as Messenger of OecemberDecember 1988). port of the R.R.A.S.A. S. Working Group for weilwell as for other reasons, a legal status FHA = Files Head of Administration at ESO study of the matter. for the Board would have been required, Headquarters. [22] See minutes of this meeting and Ooc.Doc. the accomplishment of which for an in­in- EHPA = ESO Historical Photographs Ar-Ar­ FHA Cou-2 CL 2399 of Nov. 14, 1968. ternational organization would have chives.

SN 199011990 1 in the Polar Ring Galaxy NGC 4650 A L. PASQUINI, ESO

1. ABriefA Brief History an old one taken about 10 years ago. end of the same night we managed to On the night of April 29/30, 1990, From a first glance at the plate, it was obtain 2 CCD frames (B and V filters) at Oscar Pizarro, night observer assistant clear that the object was likely to be a the ESO-MPI 2.2-m telescope. Although at the ESO Schmidt telescope found on new supernova. the observations were performed at a an ESO Schmidt B plate taken on 27.1 The host galaxy turned out to be NGC very high airmass (~2),(-2), we succeeded h m 8 0 April 1990, a new, rather luminous ob­ob- 4650 A (a = 1212h 4242m 0505', , Ö6 = -40-40' 26' in obtaining quite accurate photometry; ject, situated very close to the edge of a 30",30, 1950 Equinox) with the object 10­lo- the mean values were (29.4 April 1990) quite bright galaxy. The discovery was cated 14 arcsec east and 47 arcsec V = 15.6 and B = 16.7. Due to the loca­loca- made by comparing the new plate with south of the galaxy nucleus. Before the tion of the object and to its brightness

34 FlQureFigure 1:1: TheThe 18ftleft picturepicture showsshows aa 2.2-m2.2-m 'CCD'CCD exposureexposure ofof SN 1990119901 i'Iin NGC 46SQA4650A inin thethe VV band.band. The The SN isis thethe brightbright object,object, cIoseclose toto rhethe southemsouthern endend 0'of thethe polarpolar ring.ring. nIt isis absentabsent onon thethe picturepicture toto thethe rightright whidJwhich has beefIbeen reproducedreproduced fromfrom aa 9O-minut890-minute tJXPOSUr8,exposure, obtained inin 1977 withwith rhethe ESOESO 3.6-m3.6-m telescop8telescope onon f11a-JIlla-J emutsion.emulsion. NorlhNorth isis upup andand east isis toto thethe 18ft.left.

(see(see Fig. 1) we were confident thaithat we after maximum. For the time being it is 1980, Danziger et al., 1990), Ib super­super- were dealing with a new supernova not possible to distinguish between novae show prominent OllinesOI lines (GaskeIl(Gaskell (Pizarro(Pizarro elet al., 1990). these twotwo possibititiespossibilities by rneansmeans of opti­opti- et al., 1986). InIn order to learn the type of this SN, a cal observations, but the differences 00·be- 30-min. spectrum was obtajnedobtained the Iweentween type la'sla's and Ib'sI b's should 00be elearclear 2. SN 199011990 1 and the Host Galaxy following night (April 30.1) at the ESO --200200 days after maximum. In fact, alat 1.52-m telescope equipped with the that stage, while lala spectra are domi­d;mi- NGC 4650A4650 A is probably one of the BoIlerBoller and Chivens spectrograph nated by Fell and Felll lines (Meyerott, best studied polar ring galaxies (Laust- altached.attached. The spectrum, flat"at fieldf1eld corrected and sky subtracted, is shown in Figure 2. By comparing the pro~inentprominent XU475 SN SKYANOFFCORR features between 5400 and 6800 A with I r='-'--"'=='------.--,1B47S 9'1 5IO'NII'F'tXM published SN spectra (e.(e.g.g. Branch et al. 9 1983) and considering the observed col-col· our index and the absolute magnitude of the SN (Heliocentric velocityvelocIty of NGC 4650 AA- = 2904 km sec-',sec-I, Whitmore et ! al., 1987), it appears that SN 1990 1I is a supernova of typetype la, -40 days after thethe maximum (Pasquini, Jarvis and Leibundgu!,Leibundgut, 1990). @r, A careful analysis of published data . on type IIbb supernovae (Harkness et al., 1987), however, shows thatthat spectra and E2 colours of aalb Ib supernova -20- 20 days P after maximum can be00 almost identicalidentical to10 thosethose of a SN la which isis only fewfew SQ5. 111 (1115 • 111 111 ll52i. m weeks older;eider; we cannot thenIhen exclude FigureFIgure2: 2: 30-minute~minute BollerBoIler andand Chivens spectrumspecttum ofo( SN 1990119901 takenraken at thethe ESOESO 1.5-mI.S-rn thatIhat SN 1990 1I isis aa IIb b SNSN 2-32~3 weeks telescope.telesoope. TheThe spectrum,spectrum, wavelength calibrated, isis corrected forfor flatRat fieldfi8Id andand skysky subtracted.subtracted. 35 sen and West, 1980, Whitmore et al., have massive pragenitors. Since the 1987); in Figure 1 the ring is visible as a number of spectroscopically and photo­ Latest News disk-like feature almost oriented north­ metrically well-sampled supernovae Ib According to M. M. Phillips, CTIO, south and SN 1990 I is located close to is rather smalI, the follow-up of SN spectra of SN 19901 show that it its southern edge. Although it cannot be 1990 I is very interesting, even if it is of type Ib (IAUC 5032; June 14, exluded that the alignment of the SN should turn out not to be of type Ia. 1990). 1990 I with the polar ring is a projection The favourable location of SN 1990 I effect, it is rnore probable that the SN in the sky will allow La Silla observers to References was really formed in the ring. follow it during the next 5 months or so. The possibility that SN 1990 I is of Branch, D. et al., 1983: Ap. J. 270, 123. type la and is associated with the ring, Danziger, I.J., Lucy, L.B., Gouiffes, C., Bouchet, P., 1990: Supernovae S.E. makes this object particularly interest­ Acknowledgements Woosley ed. Springer. ing, because the ring has quite blue GaskeIl, C. M. et al., 1986: Ap. J. Left. 306, colours, is knotty and very rich in H I1 Special thanks and congratulations L77. regions indicating significant recent star go to O. Pizarro, who discovered SN Harksen, R.P. et al., 1987: Ap. J. 317, 355. formation (Laustsen and West, 1980); on 1990 I in his long-term survey of Laustsen, S., West, R. M., 1980: J. Astroph. the other hand, SN type la are typical of Schmidt plates. I also appreciate the Astr. 1, 177. galaxies in which no young stellar popu­ help of M. Bahamondes, J. Miranda and Mayerott, R. E., 1980: Ap. J. 239, 257. lation is present and it is generally J. Borquez in obtaining some of the Pasquini, L., Jarvis, B., Leibundgut, B., 1990: agreed that Ia supernovae are associ­ early observations, as weil as several lAU Circular 5003. Pizarro, 0., Miranda, J., Pasquini, L., ated with a low mass, old population visiting astronomers, who kindly spent Leibundgut, B., 1990: lAU Circular 5003. (Woosley et al., 1986). part of their time observing SN 1990 I: V. Whitmore, B.C., McElroy, D. B., Schweizer, The location of SN 19901 would not Burwitz, D. Pollacco and J. P. Sivan. Fi­ F., 1987: Ap. J. 314, 439. be unusual if, instead, we were dealing nally, I am grateful to B. Leibundgut and Woosley, S. E., Taam, R. E., Weaver, T.A., with a type Ib, which are thought to E. Oliva for helpful discussions. 1986: Ap. J. 301, 601.

The Stellar Content of the Dwarf Galaxy NGC 3109 1 2 1 F. BRESOUN , M. CAPACCIOU , and G. PIOTTo ,3 10ipartimento diAstronomia, Universita di Padova, Italy; 20sservatorio Astronomico, Padova, Italy; 3European Southern Observatory

1. Introduction spects. First, the high mass-to-light content of the universe. Observations Despite their modest appearance, ratios measured for the smallest sys­ suggest that the ratio of hidden-to­ dwarf irregular galaxies (DIGs) form an tems make DIGs some of the best can­ luminous matter increases when going interesting class of objects in many re- didates for the study of the dark matter fram irregular systems such as Sextans

• ... .. • • •

•

. .~ .. • •• ".., .•.

Figure 1: The SBm galaxy NGC 3109 trom an ESO 3.6-m 60-min exposure on Kodak II/a-J + GG 385. 36 16 I~~~~I~~~~I~~~~sewolrsservoirs of gas supports thethe bellefbelief thatthat - - dwarf Irregularsirregulars are young and st111still rela-rela­ - 9 fields 9 fields tlvelytively unevolved galaxlesgalaxies wlthwith regard toto - 8250 stars - star formatlon.formation. The question of whether 18 - - - - star formatlonformation ISis a contlnuouscontinuous process - or rather a sequence of slnglesingle bursts, 1sis - - st111still controvers~al.controversial. The burst model 1sis 20 - - usually preferred Inin lnterpretlnginterpreting the - ,. - properties of the blue compact galaxies, - , whllewhile more normal DIGSDIGs are thought to 3 .. k - - .....'-a ;"- . , - experience a contlnuouscontinuous and constant . .*, -. Y. - 2, >,-?%s,* . 22 - . . actlvltyactivity (Hunter and Gallagher, 1985). 22 - ;$p%-%3e:* ,,. ,:, :. b, .. - - . ~,2,fi~~p%$st:.+~.s>IJ::,>$+,,:, :-/ q - More than a dozen DIGSDIGs have alreadyal ready .*$P>$< ~$A$>$$~$,:&~&!$L;~;$$ h5 .+ - been ldentlf~edidentified Inin the nelghbourhoodneighbourhood of - -,&:, yi L$&:$4s-c .2:f>;-$d v+, vI; ,>' : - - , .\",.W:F;.; - the Galaxy, and so close that thelrtheir stellar SQ -:<,pi, L,: , 'i , .,- " - - 24 - ." content ISis qultequite wellweil resolved. The avall-avail­ # - - - - abllltyability of software packages allowlngallowing - - photometry ~nin crowded f~elds,fields, such as - - DAOPHOT or ROMAFOT, has permitted 26 /11111111111111,,113 the constructlonconstruction of C-M d~agramsdiagrams for a -1 1 2 - 1 0o 1 2 certalncertain number of these objects (B(B-V)-V) (Table 1). Comb~nedCombined wlthwith stellar evolu-evolu­ FlgureFigure 22: C-M dlagramdiagram of the stars prolect~ngprojecting on the 21' x 3' reglonregion centred on NGC 3109, not tion models, these measurements have corrected for f~eldfield star contam~nat~oncontamination. shed some llghtlight on the characterlstlcscharacteristics of the stellar populatlonspopulations of the nearest galaxles,galaxies, showlngshowing s~rnllarltlessimilarities Inin the~rtheir content of massive stars, as wellweil as Inin the shape of the Initialln~t~alMass Funct~on.Function. A and LGS 3 towards the smaller dwarf processes. Such processes can be We have recently undertaken a sys-sys­ spheroldalsspheroidals Ursa MlnorMinor and Draco (cf. spectacular Inin dwarf Irregulars,irregulars, espe-espe­ tematlctematic programme for the study of the TrimbleTrlmble 1987). ciallyclally inIn the blue compact galaxies.galax~es.The stellar populations inIn some nearby DIGsDIGS Second, sinceslnce DIGsDIGS are generally be­be- intenseIntense activityactlvlty relatively to the small through multicolourmultlcolour CCD photometry. lievedlleved to be simpleslmple and rather unevolved sizes of these galaxiesgalaxles accounts for theirthew MaterialMaterlal has alalreadyready been collected for objects, they are excellent laboratorieslaborator~es blue colours and for the presence of UKS 2323, IC 1613, and NGC 3109, and to study the early phases of the chemi­cheml- several associationsassoclatlons of young stars; the a firstflrst account of the results obtainedobtalned for cal evolution of galaxies.galaxles. Spec­Spec- latter are often embedded inIn large UKS 2323 has been givenglven by CapaccioliCapaccloll trophotometrictrophotometrlc investigationslnvestlgatlons have re­re- clouds of ionizedlonlzed hydrogen, and give et al. (1987). Here we present some new vealed that the metal content is1s general­general- these galaxiesgalaxles theirthelr clumpy and knotty results concerning a classical photo­photo- ly low, ranging from approximately a few appearance. The availabilityavallablllty of great re- metriemetrlc target, NGC 3109.31 09. hundredths to half of the solar value. The low metallicitymetalllc~tyis1s of consequence inIn cosmology, sinceslnce it~tfavours the estimateestlmate of the primordialpr~mordlalabundance of Helium,Hehum, a figureflgure of paramount importancelmportance inIn testingtestlng the BigBlg Bang theory. Further­ Further- . . ", "' , .: .. ' s . more, DIGsDIGS are probably the most com­corn- . ":~'..? :,. : . . ' y ., .. :' . . , • " .." , ..-',.;2.,, .zj: ..: . , . mon galaxiesgalaxles inIn the universe; thisthls too *.. . . . ': . .. ; .. a. Lr++o. :,:.,:* . - I. can be of cosmologicalcosmolog~calinterestInterest inIn that it~t .. . . e . * ...... * bears on the theoriestheorles of galaxy forma­forma- ..: . tiontlon as weil well as on the estimateestlmate of the total mass of the universe. • lSO.l> 0.1 mag, or xX> > 1.8 (Stetson, 1987), and were thus rejected. As can be seen, thethe br~ghtestbrightest stars of the main sequence have V = 18, wh~chwhich corresponds toto Mv -= -8.- 8. We l~kelike ••9 to stress here that, fromfrom thethe polntpoint of view of surface covered and number of FigureF~gure4:4. MosaicMosalc of threethree GGOCCD frames of NGGNGC 3109, centred on the west end of the bar and 'Iew Of surface 'Overed and number Of takentaken throughthrough an HaHu filter.f~lter stars measured, ours ISis one of thethe most complete CCD samplings of thethe stellar

2. NGCNGC 3109: Observations and TABlETABLE 1:1: Stellar photometry in dwarf irregular galaxies DataData Reduction Object OistanceDistance Ref. Material No. of stars NGCNGC 3109 = DDO 236 (Fig.(Fig. 1) is a modulus used measured magellanicmagellanic spiral locatedlocated at the peripheryperiphery of the Local Group: itsits dis­dis- NGeNGC 6822 23.5 mag 1 phot. - tancetance modulus, based on Cepheids, is 2 CCDeeo 3475 leIC 1613 24.5 3 phot. 318 (m-M)B(m-M), = 26 according toto Sandage and - 4 CCDeeo 2224 Carlson (1988;(1988; hereafter referred to as WlMWLM 25.0 5 phot. 68 SC). While comparable toto the Small 6 CCDeeo 2250 MagellanicMagellanic Cloud from thethe point of view lGS3LGS 3 25.0 7 CCDeeo 66 of luminosity (MB(MB = -16),-16), thethe size of GR8GR 8 25.7 8 CCDeeo 84 NGCNGC 3109 makes itit one of thethe largestlargest 9 CCDeeo 142 magellanicmagellanic systems known so far (D = UKS 2323 26.0 10 CCDeeo 204 1414 kpc,kpc, corresponding toto 09O? 5 on the NGeNGC 310931 09 26.0 11 phot. - sky).sky). Previous studies of its stellar con­con- 12 phot. 83 Pegasus 26.1 13 phot. 54 tenttent are by Demers et al. (1985)(1985) and by Pegasus 14 CCDeeo - SC; both of themthem are based on photo­photo- Sextans A 26.2 15 phot. 70 graphiegraphic material. 16 CCDeeo 652 Our observations were made during 17 CCDeeo 2279 threethree different runs runs at ESO, La Silla, inin Sextans B 26.2 18 phot. 77 MarchMarch and May 1988, and inin March 19 CCDeeo 1273 1989,1989, with thethe CCD cameras of the Dan­Dan- leoLeo A 27.1 20 phot. 92 ishish 1.5-m1.5-m and thethe ESO/MPIESOIMPI 2.2-m tele­tele- 21 phot. - 27.3 phot. scopes.scopes. We collected BandB and V images of Sculptor 27.3 22 phot. 33 HolHo l 27.5 23 CCDeeo 279 1111 fieldsfields of thethe galaxy, distributed inin Ho 11II 27.5 23 CCDeeo 468 suchsuch a way as toto cover a totaltotal area of Ho IXlX 27.5 24 CCDeeo 367 ~-21'21' x 2'. The six central fields were 000187DDO 187 28.8 25 CCDeeo 77 also imaged through an Ha filter (and in a contiguous band). Deep exposures and fair seeing conditions (FWHM ;== References 0':9-10"-1!2), ':2), allowed toto measure stars (1) Kayser, S.E., 1967, Astron. J.,J, 72,134;72, 134; (2) Hoessel, J.G., and Anderson, N., 1986, Astrophys. J.J Suppl. down toto magnitude V = 24 using DAO­DAO- SeroSer. 60,60,507;507: (3) Sandage, A.,A, and Katem, B., 1976, Astron. J.,J, 81,743;81, 743; (4) Freedman, W.W.L., L., 1988, Astron. J.,J, 96, 1248; (5) Sandage, A., and Carlson, G., 1985, Astron. J., 90, 1464; (6) Ferraro, F. R., Fusi Pecci, F., Tosi, PHOT.PHOT. InstrumentalInstrumental magnitudes were 96, 1248; (5) Sandage, A, and Carlson, G., 1985, Astron. J, 90, 1464; (6) Ferraro, F. R., Fusi Pecci, F., Tosi, M., and Buonanno, R., 1989, ESO preprint; (7) Christian, C., and Tully, R.B.,R. B., 1983, Astron. J.,J, 88, 934; calibratedcalibrated by a large set of standard (8) Hoessel, J.J.G.,G., and Danielson, G. E., 1983, Astrophys. J.,J, 271, 65; (9) Aparicio, A.,A, et al., 1988, Astron. starsstars (Landolt(Landolt 19831983a,a, b). The zero point Astrophys. Suppl. Ser., 74, 375:375; (10)(lo) Capaccioli, M., Ortolani, S., and Piotto, G., 1987, inin Proceedings of01 the errors of our photometry are estimated ESO Workshop on "Stellar Evolution and Dynamics in the Outer Halo of01 thethe Galaxy, ed. M. Azzopardi and F. Matteucci, p. 281 ; (1 1) Demers, S., et al., 1985, Astron. J., 90,1967; (12) Sandage, A., and Carlson, G., 1988, toto be ~-0.030.03 mag in V and 0.05 mag in Matteucci, p. 281; (11) Demers, S., et al. , 1985, Astron. J, 90, 1967; (12) Sandage, A, and Carlson, G., 1988, Astron. J,J., 96, 1599; (13) Sandage, A,,A, 1986, Astron. J.,J, 91, 496; (14) Hoessel, J.G., and Mould, J.J.R., R., 1982, (B-V).(B-V). Note that thethe comparison of Astrophys. J,J., 254, 38:38; (15) Sandage, A.,A, and Carlson, G., 1982, Astrophys. J., 258, 439; (16)(16) Hoessel, J.G., ~-200200 stars in common with SC has et al., 1983, Astrophys. J,J., 274, 577; (1(17) 7) Aparicio, A,,A, et al., 1987, Astron. Astrophys. Suppl. Ser., 71, 297; revealedrevealed thethe presence of a systematic (18)(1 8) Sandage, A,A,, and Carlson, G., 1985, Astron. J.,J, 90, 1011019;9; (1(19) 9) Tosi, M., et al., 1989, The Messenger, 57, 57; (20) Sandage, A., 1986, Astron. J., 91, 496; (21) Demers, S., et al., 1984, Astron. J., 89, 1160; difference in thethe zero point, our photom­photom- 57; (20) Sandage, A, 1986, Astron. J, 91, 496; (21) Demers, S., et al., 1984, Astron. J, 89, 1160; (22) Lequeux, J., and West, R.R.M.,M., 1981, Astron. Astrophys., 103, 319; (23) Hoessel, J.G.,J. G., and Danielson, etry being 0.3 mag brighter thanthan SC's; inin G.E., 1984, Astrophys. J,J., 286, 159; (24) Hopp, U., 1987, preprint. (25) Aparicio, A.,A, et al., 1988, Astron. other words, our scale implies a dis- Astrophys. Suppt. Suppl. Ser., 74, 367. 38 (Fig. 4). They are weilwell confined to a ~-300300 pc thick stripe, with a maximum Fl density a few arcminutes to the west of the optical centre. We have drawn the isophotes of these regions, and superimposed the blue star distribution. In general, the brightest blue stars and the main stellar associations are found i~ " 21 22 1 22 1.4]1.41 shown in the lower panel of the same figure. The photometric data base 24 1 . 24 pertains to 11 fields, covering more than - 20' of the galaxy in the direction of the 26 - I I I \ I I I I I I I I I I 26 -1 1 2 3 -1 0 1 2 3 long axis. - 1 0 1 2 -1 0 1 2 3 (B-V) (B-V) The central bar of NGCNGC3109,3109, de­de- 16 I , I 16 scribed by de Vaucouleurs and Freeman Vv - D1DI Vv D2 - region HlH1 region 18 18 (1972), stands out in the blue map, to­to- 1 10' gether with the two eastern spiral arms, which are weilwell seen in wide-field photo­photo- 20zo 20 graphs. Moreover, the overall distribu­distribu- 1 10' tion of the blue stars appears rather 22 22 ~ clumpy. These structures are absent or barely visible in the red map, where 24 - - 24 stars seem more evenly distributed. We l,l:~llOn~ do not measure any appreciable differ­differ- 26 IIII~IIIIIIII26 Ll-'-L-l-L..!-l---'----'---L-l-'--'----'---'---L-Ll--'---J -1- 1 0 1 2 3 -1- 1 0 1 2 3 ence in the scale heights of the two (B-V) •' (B-V) populations of stars. Figure 6: C-M diagrams of four star-forming regions. Isochroneslsochrones provided by C. Chiosi and The distribution of the young blue calculated for a solar metallicity have been matched to the observations, allowing an arbitrary stars has also been compared to that of shirtshift in colour. The corresponding ages (in years) are indicated. 39 sizes and ages of the selected regions are shown). A comparison with similar work on other resolved DIGsDIGSshows that thethe levellevel of recent star formationformation inin NGC 3109 isis quite high, a factfact which is prob­prob- ably related toto thethe size of thethe galaxy.

040 10 0 20 10 20 o 60 200 0 Acknowledgements 20 10 0 0 c() 20 o 0 0 0 20 20 40 We are indebtedindebted toto thankthank G. Bertelli, 40 0 6 10 2010 0 0 C. Chiosi, and E. Nasi, forfor providing us 0 0 40 20 o 20 00 00 6 0 with the isochronesisochrones for for thethe massive 10 o 10 0 10 o 20 10 stars inin advance of publication. We also 20 thankthank S. Ortolani for the Danish obser­obser- vations.

References Capaccioli, M., Ortolani, S., and Piotto, G., 1' G., 1987, in Proceedings of thethe ESO Work­Work- shop on "Stellar Evolution and Dynamics in the Outer Halo of the Galaxy", eds. M. Azzopardi and F. Matteucci, p. 281. Demers, S., Kunkel, W.W.E.,E., and Irwin, M.J., 1985, Astron. J. 90,1967.90, 1967. Figure 7: Map of the star-forming regions seleetedselected in the six eentralcentral fjelds; fields; the radi! radii of the de Vaucouleurs, G., and Freeman, K. K.C.,C., 6 eire/escircles are proportional to the size of the regions. Ages (in 10lo6yr) of the youngest stars found in 1972, Vistas Astron. 14, 163. the C-M diagrams are indieated.indicated. Humphreys, R.R.M.,M., 1983, Astrophys. J. 269, 335. Hunter, D.A,D.A., and Gallagher, J.S., 1985, As- isis accurate enough to get an estimate of NGC 3109 have ages of the order of trophys. J. Suppl. SeroSer. 58, 533. the agageses of the single regions. We have ~- 6 x·1x 10O6 6 years, with masses ~- 30 MG);Ma; Landolt, AU.,A. U., 1983a, Astron. J. 88, 439. used models calculated for a solar inin other words, this galaxy isis still active Landolt, AU.,A. U., 1983b,1983 b, Astron. J. 88, 853. metaliicitymetallicity and adopted the internal ab­ab- in forming stars. Moreover, since the Piotto, G., King, I.I.R.,R., Capaccioli, M., Ortolani, sorption values given by SC. A larger part of the diagrams corresponding to S., and Djorgovski, S., 1990, Astrophys. J. 350,662.350, 662. extinction correction had to be adopted agageses of 20-100 million years appears Sandage, A.,A, and Carlson, G., 1988, Astron. for star-forming regions belonging to the rather uniformly populated by stars, we J. 96, 1599. central parts of the galaxy. An example may conclude that, in this time interval, Stetson, P.ß.,P. B., 1987, P.A.S.P.P.A. S. P. 99,191.99, 191. of the procedure is shown in Figure 6. stars have formed in an almost regular Trimble, V., 1987, Ann. Rev. Astron. Astro-Astro­ We find that the youngest stars of manner (see the plot in Fig. 7, where phys. 25, 67.

Probing the Hidden Secrets of Seyfert Nuclei I. AAPPENZELLER PPENZEL LER and S. WAGNER, Landessternwarte Heidelberg-Konigstuhl,Heidelberg-Königstuhl, F. R. Germany

The nuclei of active galaxies are clear-clear­ rates up to about one earth mass per became increasingly evident that in ly among the most spectacular and vio-vio­ second, such black holes give rise to many AGNs the central engines are lent places that can be found in our huge rotating magnetic fields and elec-elec­ not directly visible but hidden behind present universe. Most extreme are the tric current systems which can explain opaque dusty matter concentrations bright Quasars, where we observe a to-to­ the astonishing properties of these sys-sys­ along the line of sight. Even in the case tal energy output equivalent to a large tems. of nearby Seyfert galaxies (the nearest galaxy cluster from galactic core regions However, in spite of a large research known examples of AGNs), direct opti-opti­ comparable in size to our solar system. effort during the past decades we are cal radiation from the centre of the ac-ac­ In addition to optical and radio radiation still lacking a reliable observational con-con­ tive nuclei seems to be observed only in we often observe intense X-ray and firmation of the basic physical models of exceptional cases. Moreover, when di-di­ even energetic Gamma radiation as wellweil the AGNs and our knowledge of the rect radiation is detected, it is often mix-mix­ as collimated streams of matter moving detailed physical processes occurring in ed with light of the normal stellar galac-galac­ at velocities close to the velocity of light. AGNs is still highly incomplete. One tic core and with emission from circum-circum­ Most currrent theories assume that reason for the slow progress of our nuclear normal HI1H 11 regions ionized by the enormous radiation power of active understanding of the AGNs is the great stars. galactic nuclei (AGNs) isis produced by distance of most active galaxies which Fortunately, modern observing tech-tech­ massive rotating black holes residing in makes it impossible toto resolve thethe active niques provide various methods toto over-over­ thethe dynamical centres of thesethese galaxies. nuclei by direct imagingimaging techniques.techniques. come some of thethe observational difficul-difficul­ Swallowing surrounding material at Furthermore, during thethe past decade itit tiesties mentioned above. High-resolution 40 spectroscopy often allows to separateseparale theIhe different components which contri-contri· bute to Ihe the (on direct images) unre­unre- solved galactic cores. When the galactic cores are hidden from us by local dust absorption, theirIheir radiation fields can sometimes be delermineddetermined indirectly from!rom its effeclseffects on theIhe interstellar gas in theIhe host galaxies. Finally, recent pro­pro- gress in infrared imaging techniqueslechniques makes it possible to penetrate part of the absorbing dust layers and to look deeper into the hidden central regions of the AGNs. In this paper we shall report about our experience with these methods at theIhe ESO telescopes during various recenl recent observing runs. Because of limited space we shall restrict this report mainly to10 resullsresults on the two particularly inter-inter­ esting emission line galaxies NGC 5728 and IC 5063. NGC 5728 is a prominent barred spiral with a Seyfert 2 nucleus. An account of its basic properties and a photographic image of this galaxy can be found in an earlier issue of theIhe Messenger (cf. [1)).[I]). IC 5063 (= PKS 2048-572) is an early-type radio galaxy known mainly for its pronounced dust lanes. In In addition to data on these two galaxies, a few resullsresults on theIhe prototypeprotolype Seyfert 2 galaxy NGC 1068 will be re­re- ported.

Improving the Angular Resolution by Means of Spectroscopy In the optical spectral range AGNs are usuaUyusually identified by the characteristic emission line spectra produced in their Broad-Line and Narrow-Line AegionsRegions (BLAs(BLRs and NLRs).NLAs). Compared to most stellar spectra even the NLANLR spectral features are rather broad and have Dop­Dop- pler widths of.severalof-several hundred km S-1s-' or more. Hence, on first glance itit seems not to make sense to observe theseIhese spectra with high spectral resolution. However, as illustrated by FiguraFigure 1, high resolution spectra of AGNs can in fact provide importantimportant information.informalion. The up­up- NGC 5728 [0 IIIJ 5007 per part of Figure 1 shows long-slit spectrograms of the Ha and [N[NII]It] X 6584 A lines of NGC 5728 obtained with :::J A -' the ESO CASPEC spectrograph.speclrograph. The CL horizontal coordinate corresponds to10 . wavelength (expressed as a relative -' Doppler velocity) while the vertical coor-coor­ W dinate gives the location of the emission along the projected spectrograph slit. '" along the projected spectrograph slil. I---~--~- The centcentresres of the two langlong slilslit spectra ------,_ ------__ correspond (in velocity) to10 the systemic I ; 1 velocity of NGC 5728 (as derived from -l~~~ -5~~ ~ 5~~ l~~~ the absorption lineslines of the stellar com-com­ - 1000 -500 0 500 1000 REL.RH. VELOCITYVEL OC/ T Y [KM/5JCKM/SJ ponent) and (in space) to theIhe dynamical centre of Ihethe galaxy. Hence, a mono­mono- chromatic light source emitlingemitting the cor­tor- Figure 1: Emission-lineEmisslon-line profiles of0' the nucleus of NGC 5728. On top are long-slitlong-sllt spectrograms responding spectral lines and moving of the cores of Ihethe Ha and [NII]{Nil] 6584 profiles, oblainedobtained wilhwith an EW slit orien/allon.orientation. Below isIs a with the centre of NGC 5728 would pro- lracingtracing (oblalned(obtained by integratingIn/egraling along theIhe slit)slil) of the full {Dill}[0111] 5007 profile.

41 [0111][OIII] 5007 Aline (Iower(lower part of Figure 1),I), where the unresolved component corre­corre- EAST sponds to the redshifted peak. A velocity difference of more than 200 km S-1s-' between the whole NLR and the dynamical centre of its host galaxy appears highly unlikely in all current AGN models. Hence, it seems much more plausible to explain the spectros­spectros- copic results by assuming that in the case of NGC 5728 only the red wing of the NLR profiles is observed, while the matter producing the rest of the NLR profile (i.e., in fact, most of the NLR) is hidden from us by dust absorption. With a slightly larger amount of dust absorp­absorp- tion NGC 5728 could probably not even be recognized as an active galaxy. +0',' 5 Another example of the effects of cir­cir- cumnuclear dust in an AGN is shown in Figure 2, where we reproduce line pro­pro- file tracings obtained for points on the major axis of the galaxy IC 5063 at vari­vari- ous distances from the centre of the >< ==> active nucleus. As the line again con­ con- .....J u.... tains contributions of different volumes with different line widths and radial ve­ve- .....J -0',' 5 UJ locities, the NLR profile changes with 0::: distance from the centre. A surprising detail of Figure 2 is the fact that the profile observed at the centre is relative­relative- Iyly narrow, while conspicuous broad line wings are present about 1':5lf.'5 (corre­(corre- sponding to about 500 pepc at the dis­dis- tance of IC 5063) NW of the dynamical -1',' 5 centre. By separating the observed pro­pro- files into individual emission compo­compo- WEST nents, it can be shown that the broad wings are produced by a local emission 5070 5080 region with a velocity width of about 5040 5050 5060 900 km S-1s-' (cf. [4]). Such broad line WAVELENGTH [ÄJ components are expected to form only in the central regions of AGNs. The fact Figure 2: Emission-line profiles at different angular displacements from the core of IC 5063. that such a broad emission profile is found from a region far outside the centre strongly suggests that we ob­ob- serve nuclear light which is scattered by duce a point in the centre of each of the ical conditions. As most of these emis­emis- dust clouds which are located outside two images, while an extended mono­mono- sion components are concentrated in the nuclear region and whwhichich are ex­ex- chromatic source would produce a ver­ver- the innermost two arcseconds of the posed to radiation from the nucleus. ticalline.tical line. nucleus they cannot be resolved on di­di- Since no broad wings are detected in As shown in Figure 1, due to the vio­vio- reetrect images but become visible only on the radiation reaching us from the direc­direc- lent motion of the nuclear gas the line long slit spectrograms of sufficient tion of the nucleus, we again have to emission is distributed over a significant spectral resolution. conclude that along our line of sight the velocity range, producing the charac­charac- A more detailed investigation (cf. [3]) core of the AGN is hidden by dust and teristic complex line profiles of the NLR shows that most of the emission line that only indirect radiation is able to (cf. [2]). Moreover, the emission is also regions seen in Figure 1 correspond to reach us at visible wavelengths. smeared out in spatial direction. Al-AI­ measurably extended volumes of gas. though atmospheric seeing contributes Only the strongest component shows Only the strongest component shows The ENLR Connection to this spatial extension, Figure 1 (ob­(ob- the angular intensity distribution of an tained with :s50f.'80':8 seeing) clearly shows unresolved point source. This compo­compo- In addition to producing scattered that much of the observed spatial extent nent must correspond to the true Sey­Sey- light, the intense radiation field of the is caused by the superposition of indi­indi- fert nucleus. Surprisingly, the nuclear AGNs can also ionize the interstellar vidual emission regions with different emission, although projected on the dy­dy- matter of their host galaxies. Depending velocities and spatial locations. The namical centre of the galaxy, does not on the UV flux and the matter distribu­ distribu- highly different relative intensities of the have the systemic velocity of the galaxy tion, the ionization effect may be signifi­signifi- individual components in the two line but shows a velocity shift of more than cant even at distances of many kpc from profile images show that the emitting 200 km S-1.s-'. This velocity shift is even the nucleus. The resulting "extended gas volumes vary greatly in their phys- more conspicuous in the tracing of the narrow line regions" (ENLRs) show the 42 radiation from the centre of this AGN is visible in our line of sight. NGC InfraInfraredred Imaging Since the scatteringscauering and absorption cross sections of typical interstellar dust grains decrease with increasing wavelengths, dust absorption is most severe in blue images of galaxies and becomes less important at red and in­ in- frared wavelengths. Therefore, dust ab-ab­ sorption features are usually traced most efficiently by means of "ratio im­im- ages" which are generated by calculat-calculat­ ing thethe ratios 01of corresponding pixels of two images obtained at different wavelengths. An example, showing the ratio betwoonbetween a visual (V-band) image and near·infrarednear-infrared (I-band) image of IC 5063 (observed by C. MollenhoffMöllanhoff and P. Surma), is given in FigureFigura 4. As the dust absorption is weaker in the I-band (cor-(cor­ responding to about 0.85 pm)j.tm) than in the V-image (central wavelengthwavalength =-0.550.55 11m)pm) dust features appear darker in the ratio image. Figure 4 shows a particularly prominent dust lane just north of the nudeus.nucleus. Since it almost coincides with the nucleus, it certainly affects the light reaching us from the core of this galaxy. The nucleus itsellitself appears in the ratio image as a double peak. This is readily-. explained bv by theIhe fact that its visual image is (due(die to stronger dust absorption) and a stronger contribution of extended line emission in the V-band)V-band} elonaatedelongated while its I imageimaae., Figure 3: Fa/sa-c%urFalse-colour map of thathe extandadextended (Dill)[0111] emission of NGC 5728. is more circular. -

same (nonthermal) ionization charac-charac­ teristics as the nuclear NLRs (and thus are easily distinguished from normal H IIn regions), but (due to lower internal ve-ve­ locities)locities) differ from the NLRsNLAs by much narrower line profiles. Figure 3 shows the ENLR of NGC 5728 as outlined by its [OIU)[OIII] emission. As demonstrated by the figura,figure, most 01of the obsarvedobserved ENLAENLR emission is found in two relativelyrelativelv narrow cones extendinaextending towards the SE and NW directions fror;from I the nucleus. Interestingly, the axis de-de­ fined by these two cones also coincides (at least in projection) with a jet-like re-re­ gion of enhanced radio emission (cf. [5)).[5]). L Such coaxia!coaxial morphologies have also been found for other AGNs and have been interpreted as evidence for central radiation fields and relativistic particlepartide flowsIlows directed mainly parallel to the ro-ro­ tation axis 01of the nucleus, while the radi­radi- ation perpendicular to the rotation axis is blocked bybya a disk of dusty gas clouds. If this explanation is correct, and ifif the radiation cones of NGC 5728 are indeedindeed oriented as suggested by Figure 3, it is FiguraFigure 4: V/IV/l ratio map of the centra/central part of0' IC 5063. ThaThe imageimage covers about 2' x 2!5.2:5. North is obviously no surprise that little direct up, eastaast to the leftleft.

43 NGCNGC 57285728 N J (1.251') \ ...... ,.., "",

~ ..

E

.. ...•.• ;'

-5.0" .2.5" o +2.5" +5.0"

v···· J..'

.... _--.

, I .../ FigureFigure6: 6: False-c%urFalse-colour mapmap o(of thethe Brackett-gammaBrackett-gammaemission emission fromfrom thethe corecore o(of NGCNGC 1088.1068. TheThe / continuumcontinuumhas has beenbeensubtracted subtracted byby meansmeans o(of anan imageimageobtained obtainedin in anan adjacentadjacent narrOwnarrow line-(reeline-free ,,' continuumcontinuum band.band. TheThe imageimage covetScovers aa fieldfield o(of 38'38" xx 48-.48: '.. " >-..~ 4.'~'" b e, .. usedused ESO'sESO's newnew IRACIRAC infraredinfrared arrayarray (3)).[3]). AllhoughAlthough thethe J-bandJ-band emissionemission cameracamera (cf.(cf. [6),[6], (7J)[7]) toto obtainobtain imagesimages ofof reachesreaches itsits maximummaximum intensityintensity inin thethe ~... severalseveral dustydusty SeyfertSeyfert nucleinuclei inin Ihethe JJ centre,centre, nono dislinctdistinct pointpoint sourcesource corre·corre- (1.25(1.25 Ilm),pm), HH (1.65(1.65 j.lmj,pm), andand KK (2.2(2.2 j.lm)pm) spondingsponding toto thethe nueleusnucleus cancan bebe de­de- bands.bands. BecauseBecause ofof poorpoor wealherweather condi­condi- lecled.tected. TheThe {in(in FigureFigure5 5 omitted}omitted) lower­lower- tionstions andand variousvarious teehniealtechnical defieieneiesdeficiencies inlensityintensity oulerouter cantourscontours ofof thethe J-bandJ-band ) ofof thethe 3232 xx 3232 pixelpixel HgCdTeHgCdTearray array avail­avail- inlensilyintensity dislributiondistribution becomebecome elongaledelongated .~. ableable toto us,us, ourour runrun waswas onlyonly aa partialpartial alongalong thethe (NE-SW)(NE-SW) MajorMajor axisaxis ofof thethe suecess.success. InIn thethe easecase ofof NGCNGC 57285728 onlyonly galaxy,galaxy, indicalingindicating aa low-Ievellow-level "'®"b:'.....- "\ ,", ~~'-"( J-bandJ-band imagesimages ofof suffieienlsufficient S/NSIN couldcould backgroundbackground producedproduced byby Ihethe slellarstellar ..... -~ 1\ :"., bebe oblained.obtained. TheThe ICIC 50635063 observationsobservations component.component. TheThe extendedextended IRIR radiationradiation (\ werewere moremore successful,successful, yieldingyielding imagesimages fromfrom thethe corecore regionregion isis probablyprobably alsoalso , ...., ~. ofof reasonablyreasonably goodgood S/NSIN inin allall threethree con­con- dominateddominated byby starlight,starlight, althoughalthough ex­ex- "'. " -"." ' .. -·, .. f'· tinuumtinuum bandsbands andand wilhwith differentdifferent fieldfield tendedtendedline lineemission emission(e. (e.g. g. ofof thethePaschen Paschen Je 5063 .1:', sizes.sizes. lineslines ofof hydrogen)hydrogen) maymay conlribute.contribute. H (1.65,,) ExamplesExamples ofof isophoteisophote mapsmaps derivedderived MoreMore interestinginteresting areare thethe mapsmaps ob­ob- -5.0"-5.0" -2.5"-2.5" 00 +2.5"+2.5" +5.0"+5.0" fromfrom ourour IRIR imagesimages ofof Ihethe eorecore regionsregions tainedtained forfor ICIC5063. 5063. InIn allall threethree IR-bandsIR-bands FiguraFigure5: 5: ExamplesExamplesof ofbroad-band broad-bandimages imagesof of ofof NGCNGC 57285728and andIC IC 50635063 areare presenledpresented thethe observedobserved radiationradiation waswas foundfound toto thethecores cores 0'of NGCNGC5728 5728and and IClC 5063.5063. inin FigureFigure5a 5a andand c.c. InIn FigureFigure5b 5b wewe consistconsistof of threethreedislincl distinctcomponents. components.As As showshow forfor eomparisoncomparisona aV-band V-band isophoteisophote illustratedillustrated byby FigureFigure5 5c,c, thethe outerouter con­con- mapmap ofof Ihethe samesame areaarea ofof ICIC 5063.5063. 80lhBoth tourstours showshow anan elongationelongationalong along 1hethe ma­ma- IRIR isopholeisophote mapsmaps areare basedbased onon imagesimages jorjor axisaxis ofof thethe galaxy.galaxy. TheThe correspond­correspond- oblainedobtained withwith eircularcircular pixelspixels ofof aboutabout inging low-Ievellow-level exlendedextended emissionemission againagain TheTheratio ratioimage imageof of FiguraFigure4 4 showsshowsthai that 0':160'116 diameterdiameter withwith aa 0':50'15 spacing.spacing. TheThe seemsseems totooriginate originatefrom from thethe stellarstellar eom­com- I-bandI-band imagesimages (corresponding(corresponding 10to thethe (FWHM)(FWHM) resolutionresolution (limiled(limited byby thethe see­see- ponent.ponent. SuperimposedSuperimposedis is aa small,small, aboutabout langestlongest wavelenglhwavelength bandband thaithat cancan bebe ing)ing) isis aboulabout 11'12.~2. TheThe VV mapmap (based(based onon circularcircular extendedextended {diameter(diameter ""'4'1-4") regionregion efficientlyefficientlyobserved observedwith with normalnormalSi Si eCDCCD 0':350'135 denselydenselypacked packedand andquadralie quadraticpix­ pix- whichwhich surroundssurrounds aa prominentprominent unre­unre- detectors)detectors) areare clearlyclearly lassless affecledaffected byby els)els) hashas aresolutiona resolutionof of aboulabout 11'15.~5. solvedsolved eentralcentral pointpoint souree.source. ThereThere dustdust absorptionabsorption Ihanthan blueblue andand visualvisual AsAs 1I1ustratedillustratedby by FigureFigure4, 4, inin Ihethe easecase seemsseemsto tobe beliltle littledoubt doubtthat thatIhis this IRIR pointpoint images.images. However,However,a a detaileddetailedanalysis analysisof of ofof NGCNGC5728 5728most mostof of thetheobserved observed radi­radi- soureesource eorrespondscorresponds toto Ihethe SeyfertSeyfert nu­nu- aurour I-imageI-image showsshows thaithat Ihethe dustdust laneslanes ationationin inthe the 1.21.2 !-Imym bandband isisemitted emittedfrom from cleuscleusof of ICIC5063. 5063. AA eomparisoncomparisonof of thethe VV cancan stillstill bebe tracedtraced eveneven atat thesethese aa slightlyslightly elongatedelongated exlendedextended regionregion andand thethe HH mapsmaps ofof FigureFigure5 5 showsshows thatthat wavelengthswavelengths andand thaithat thethe morphologymorphology withwith anan averageaverage diameterdiameter ofof aboutabout r7" thethe eonspieuousconspicuous isopholeisophote distortiondistortion byby seenseen inin thethe I-bandI-band imageimage isis stillstill influ­influ- (corresponding(corresponding10 toabout about 22kpe). kpc).This This re­re- thethe dustdust laneslanes visiblevisible inin thethe VV mapmap encedenced byby thethe dustdust absorption.absorption. InIn orderorder giongion agreesagrees weilwell (in(in size,size, shapeshape andand eannotcannot bebe deteeteddetected inin thethe IRIR image,image, toto looklook behindbehind thethe dust,dust, oneone obviouslyobviously orienlalionjorientation) withwith thethearea area insideinsidethe the ringring suggestingsuggesting thatthat absorptionabsorption byby thesethese hashas 10to observeobserve atat eveneven longerlonger ofof gasgas andand starsstars whichwhich delineatesdelineates Ihethe featuresfeatures isis nono longerlonger signifieantsignificant atat thisthis wavelenglhs.wavelengths. Therefore,Therefore, wewe recentlyrecently carecoreof of NGCNGC5728 5728 ononoptical opticalimages images(cf. (cf. wavelength.wavelength. However,However, thisthis hashas toto bebe

44 confirmed by a more detailed analysis of tiesties as thethe IC 5063 frames. We again futurefuture also toto other active galaxies in-in­ all threethree infraredinfrared frames.frames. observe a bright unresolved nucleus cluding the hidden cores discussed in The physical interpretation of thethe ob-ob­ surrounded by extended emission. Sur-Sur­ thethe firstfirst chapters of thisthis paper. served extended nuclear IR emission of prisingly, our narrow-band CVF imagesimages IC 5063 isis again complicated by the inin line-freeline-free IR continuum bands turned presence of emission lineslines inin thethe threethree out toto be quite different. These imagesimages References observed infrared bands. AAseparation separation show thethe unresolved central nucleus but of the line and continuum contribution practically no detectable continuum [I][1] van Gorkom, J. H., Kotanyi, C.G.,C. G., Taren-Taren­ ghi, M., Veron-Cetty, M.P., Veron, P.: requires narrower pass bands. Such radiation from an extended circum-circum­ ghi, M., Veron-Cetty, M. P., Veron, P.: 11983,983, The MessengerMessenger33, 33, 37. narrow bands can be realized with the nuclear region. On the other hand, as narrow bands can be realized with the [2] Appenzeller, I.,1., Ostreicher,Östreicher, R.: 1988, As-As­ circular variable filter (CVF) of the IRAC demonstated by the Brackett-gamma tron. J. 95, 45. camera. However, the detector noise of line image reproduced in Figure 6, in the [3] Wagner, S.S.J., J., Appenzeller, 1.: 1988, As-As­ the present array limits this mode of light of the IR emission lines we clearly tron.tran. Astrophys. 197, 75. operation to relatively bright objects. see also extended emission surrounding [4] Wagner, S. J., Appenzeller, 1.: 1989, As-As­ From published IR line fluxes only the the nucleus. Hence, in the case of NGC tron.tran. Astrophys. 225, L 13. nearby Seyfert 2 galaxy NGC 10681068 1068 it seems clear that at least most of [5] Schommer, R.A.,R.A, Caldwell, N., Wilson, appeared to be bright enough to the extended circumnuclear IR emission A.S.,A S., Baldwin, J.A.,J.A, Phillips, M.M.,M. M., Williams, T. B., Turtle, A. J.: 1988, Astro- attempt CVF observations. As this is caused by line emitting gas. Williams, T.B., Turtle, AJ.: 1988, Astro­ phys. J. 324, 154. galaxy also belongs to the AGNs with Our results for NGC 1068 clearly [6] Moorwood, A,:A: 1988,1988, The Messenger 52, evidence for a hidden core (cf. [8]) NGC demonstrate the potential of narrow-narrow­ 50. 1068 was also included in our pro-pro­ band IR imaging for studies of nearby [7] Moorwood, A,,A, Finger, G., Moneti, A,:A: gramme. AGNs. Hopefully, improved array detec-detec­ 1988, The Messenger 54, 56. Our broad-band IR images of NGC tors and larger telescopes will make it [8] Antonucci, R.R.R.J., R. J., Miller, J.S.: 1985, As-As­ 1068 show qualitatively similar proper- possible to apply this technique in the trophys. J. 297, 621.

A Redshift Survey of Automatically Selected Clusters of Galaxies 3 4 L. GUZZOGUZZO',1, R. NICHOLNICHOL*,2, C. COLLlNSCOLLINS~,, S. LUMSDENLUMSDEN~ 10sservatorio'~sservatoriodi Brera, Milan, Italy; 20'~eparfmentepartment of Astronomy, University of Edinburgh, Great Britain; 3RoyalObservatory,3~oyalObservatory, Edinburgh, Great Britain; 4Astrophysics4~strophysicsGroup, Imperial College, London, Great Britain

IntroduetionIntroduction (&,)(~cc) is about 15 times stronger than that due. In 1988 we started at ESO a red­red- The study of the large-scale structure for galaxies ('g,,)(~gg) (see Bahcall, 1988). shift survey based on an automatic of the universe provides direct con­con- This observation is one piece of evi­evi- samsamplepie of rich clusters extracted from straints on the initialinitial form of the density dence that has prompted the ideaidea of the EdinburghlDurhamEdinburghIDurham Southern Galaxy fluctuations from which galaxies, clus­clus- biased galaxy formation (Kaiser, 1984) Catalogue. The results (so far) have ters and superclusters formed. This can and indicatesindicates that neither galaxies nor been very successful, and in this note be achieved by mapping the large-scalelarge-scale clusters can both be tracers of the mass we would like to report on the present galaxy distribution, with the assumption distribution. In the context of models of status of the project. that lightlight isis a good tracer of the underly­underly- galaxy formation the "standard cold ing mass distribution. To compare our dark matter" model (CDM) fails to pro­pro- ing mass distribution. To compare our The AutomatieAutomatic Catalogue maps with the theory, we need to ex­ vide enough power on cluster scales maps with the theory, we need to ex- ofClustersof Clusters tract some numbers describing their when normalized to fit the observed ~ggEgg properties inin a statistical sense. One of (White et al., 1987). As mentioned, the cluster catalogue thethe main properties which are of interest Given thethe prime importance of thisthis has been extracted from the Edinburgh/Edinburgh1 inin thisthis sense isis clustering, i.i.e.e. how thethe observation, it isis extraordinary thatthat we Durham Southern Galaxy Catalogue distribution of objects differs from a ran­ran- still rely on estimates of thethe cluster cor­cor- (EDSGC),(EDSGC), one of thethe firstfirst ever large­large- dom sampie.sample. This is of great import­import- relationrelation functionfunction based on "eyeball" cat­cat- scale machine-based optical galaxy ance, since theories usually give precise alogues of clusters, namely thethe Abell catalogues. This galaxy survey has been predictions about the levellevel of c1usteringclustering (1957)(1957) and Abell, Corwin, Olowin (ACO,(ACO, constructed using thethe COSMOS high­ high- on different scales. 1989) lists. Evidence has been speed microdensitometer, and consists The most popular statistical estimator accumulating about systematic and un­un- of 60 UK Schmidt J survey plates of c1ustering clustering is certainly thethe two-pointtwo-point quantifiable selection effects present in centred at thethe South Galactic Pole. The spatial correlation function ~(r),E(r), thatthat such visual compilations, giving rise toto galaxy catalogue covers an area of 0.5 ~cc measures thethe probability in excess of doubts on thethe realityreality of thethe observed Ecc steradians toto a limitinglimiting magnitude of bb,j = randomrandom of finding twotwo objects at a sep­sep- (Sutherland,(Sutherland, 1988, and see Dekel, 1989 20, with a total of ~- 1.5 million galaxies, aration rr (see(see Peebles, 1980). One of thethe forfor discussion). With thesethese uncertainties with > 95 % completeness and < 10%10% most remarkableremarkable resultsresults obtained inin thethe inin mind, thethe estimation of ~ccEcc fromfrom a star contamination (see(see Heydon-Dumb­Heydon-Dumb- lastlast fewfew years isis thatthat thethe two-pointtwo-point cor­ cor- redshiftredshift survey of objectively (i.(i.e.e. auto­auto- leton,leton, Collins and MacGillivray, 19891989 for relationrelation functionfunction forfor clusters of galaxies matically) detected clusters is long over- details). The EDSGC representsrepresents an idealideal

45 AcaACO CluslersClusters suited to investigate in detail problems -20-20- 1 1 1 1 , ' 1 1 1 Ill, IIII,IIlIII- 0 0 like subclustering, where many redshifts 0 n -25 - 000 0 0 0 - are needed on every single cluster. In 0 0 0 i =a O 0OoO0 :;:lJ -30 0o 00 O oO (i.(i.e.e. key programme) status. The total 8 2 0 O (f 0 .S.-" o000 O 0 0 0 - - number of nights allocated so far is 12, tl2 -35 0 o~ o % c0 0 ~o " - 0% 0 :.o00 0 h I0 0; over four semesters. Ouring During these two 0 -40 O O ,, 00 0 0 0 - 0 0 years of use, EFOSC has proved to be 0 0 0 - -45 '~""11"'1""1"11~1'1'~' an excellent device for this kind of red­red- 3 2 1 0 -1- 1 -2 RighlRight Ascension shift survey. With some good luck with the weather, we could observe at high Figure 1: CamparisanComparison of a subset of the EOSGCEDSGC automatieautomatic cluster eatalogue catalogue with a similar efficiency about 7575%% of the time. We subset in the same area extraetedextracted from the AGOACO eatalogue.catalogue. 80thBoth subsets eorrespondcorrespond to Abell covered 62 clusters, with a total of distaneedistance classes eS55.5. For the eomparisoncomparison of riehnessrichness classes see the text. -~ 800 galaxy spectra. The observational set-up of EFOSC includes the B 300 grism, providing a spectralspect~al coverage Jromfrom 4000 A to database for producing a cluster cata­cata- range between m3m, and m3+2.m,+2. Our first 7000 A with about 6 Npixel.A/pixel. The use of logue. candidate analysis was the same as the cross-correlation technique to mea­mea- The first step in constructing our clus­clus- Abell, as any new cluster catalogue sure the redshift reduces the actual rms ter catalogue was to produce a list of must be initially compared to the Abell errors to 50-100 km/s, depending on candidate clusters. The galaxy data (or ACO for the South) catalogue. The the S/N ratio of the spectra. With 10-1510-1 5 were binned into 5 arcmin pixels and final catalogue contains ~-300300 clusters measured galaxies per cluster we have then smoothed with a gaussian filter to with >>3030 members. Of these 6565%% are negligible errors on the mean redshift reduce the harshness of the binning. To present in the ACO catalogue, yet we «200(<200 km/s).kmls). Exposure times of 20 to avoid preferentially detecting clusters in only detect 3030%% of the ACO's clusters 30 minutes have been used to obtain high-density regions of the survey while in our survey region. Upon checking the good S/NSIN spectra for the faintest ob­ob- missing others in low-density regions, missing ACO clusters we find they are of jects (b(b,j = 19) observed. Accurate posi­ posi- we must remove the large-scale galaxy low richness, or not a cluster at all, while tions «2"),(<2),magnitudes «0.2)(<0.2) and im­im- distribution. This was achieved by heav­heav- the new non-ACO clusters are all rich age classification for all the objects in ily smoothing the pixel data with a me­me- bonafide clusters. The clusters common dian filter on the scale of 1.5 degrees to the two catalogues show slight dis­dis- and then subtracting this sky tance correlation but we find no relation­relation- background estimate. Projection effects ship between our richness and ACO have been proposed to account for part richness. In Figure 1 we show a plot of of the discrepancy between tgg~gg and ~cc.tee. the sky distribution of the Automatic We took particular care then to reduce Clusters (AC), while Figure 2 shows an their influence by deblending the candi­candi- EFOSC direct image of the central re­re- date clusters. Each of them was re­re- gions of the new cOcD cluster AC-22. thresholded at 16 equal levels above the local sky background as estimated Observational Strategy above. If any saddle-points in the can­can- didate's pixel data were found, the can­can- In 1987 while the construction of the didate was then split into its daughter cluster catalogue was in its early stages, members. After the completion of the we realized how efficiently we could redshift survey we will be able to check construct a cluster redshift survey by residual projection effects by deblend­deblend- using EFOSC in MOS mode at the ESO ing in 3 dimensions, using the mag­mag- 3.6-m telescope. We intended to ob­ ob- nitude and redshift distribution of the serve around 10-1510- 15 galaxy redshifts cluster members. The total number of per cluster on a samsamplepie of about 150 candidate clusters detected over the clusters and for this EFOSC was more 17001700deg2deg2 of the EOSGCEDSGC survey is suited than OPTOPUS, the fiber large­large- ~- 1000 (Nichol et al.,at., 1990). field multi-object facility. Indeed, with Abell estimated the distance to a clus­clus- this number of spectra and with a good ter using the magnitude of the tenth filling factor of the CCOCCD field (as it is the brightest member (mlO)'(m,,). The c1uster's cluster's case for most of our clusters) the use of richness was defined as the number of EFOSC is to be preferred to OPTOPUS galaxies within a fixed radius (scaled to both in terms of efficiency and flexibility. Figure 2: EFOSC direetdirect image of the automa­automa- the cluster distance) in the magnitude On the other hand, OPTOPUS is best tietic cluster AC-22 at redshift z = 0.1079. 46 the projeet,project, we decided last year to wavelength ealibratecalibrate the single 202 D complement ESO observations using spectra extraetedextracted from the MOS frame the AUTOFIB fiber system at the 3.9-m we use the standard commands in the Anglo-Australian Telescope.Teleseope. AUTOFIB long-slitlong~slit context (IPCS in the old is similar to OPTOPUS, but with the MIOAS).MIDAS). In Figure 4 we show a final 110 D I advantage of having an automaticautomatie fiber spectrum from the same cluster of Fig-Fig­ positioner which greatly improves the ures 2 and 3, i. e. AC-22. observing efficieney.efficiency. Indeed.Indeed, during 3 The next steps follow essentially the nights in Oetober October 1989 we seeuredsecured recipe by Tonry and DavisOavis (1979) for an another 30 clusters. optimal treatment of the spectrum be-be­ fore applying the cross-correlation al-al­ gorithm. These involve, among others, Data ReduetionReduction rebinning into logarithmic bins, elimina­elimina- The aspect that makes Multiple Ob­Ob- tion of residual spikes (emission lines, jectjeet SpeetroseopySpectroscopy so interesting and residual cosmics and sky lines), con­con- useful is the tremendous increase in the tinuum subtraction, endmasking and number of spectra that can be obtained bandpass filtering. Finally, cross-corre­cross-corre- inin one night with respect to the standard lation with several galaxy templates is method. This implies that automatieautomatic performed using the Fast Fourier Trans-Trans­ data reduetionreduction techniquesteehniques beeome become a form method. To calibrate the zero point must to avoid being overwhelmed by of01 the galaxy templates, we have also the data flow. Future MOS devieesdevices will observed high S/N nearby objects with certainly have to include as muehmuch on line very good 21-cm21 -cm redshift determina-determina­ reduetionreduction as possible, otherwise data tions. handling will become prohibitive. For the time being the astronomer has to solve Future Prospects the problem in the reduction phase. Un-Un~ I fortunately, no specific package has With another 5 nights at ESO and a Figure 3: MOS frame of galaxies in the field of been developed for this kind of data similar amount at the AAT we will be AC-22. The quality 0'of cosmic ray events insideinside MIOAS,MIDAS, and therefore we had to able to complete the first homogeneaushomogeneous eliminafionelimination through AVERAGEmNDOWAVERAGEiWINDOW is construct some routines to extractextraet and samplesampie of about 150 clusters with rich-rich­ evident. handle the single spectra from their pa-pa­ ness >30> 30 and distance classification rent multi-objectmulti-objeet frame. This implied an s555(with m,,mlO in R S5 17.2). This will then extra effort in the beginning, that how-how­ provide an excellent database for es-es~ each cluster, all information provided inin ever improved enormously the effieien­efficien- timating EccSee with a higher accuracy than the EOSGC,EDSGC, have proved to be very eycy of later reductions. Presently, reduc-redue­ previous measurements (Bahcall(Bahcali and useful to maximize efficiency. We can tion has become a routine job and we Soneira, 1983; Sutherland, 1988). produce high-quality finding charts and eancan transform a whole MOS frame into a Apart from the main goal of the sur-sur­ decide wellweil in advance where the areas set of -15- 15 1-D1-0 calibrated and sky sub-sub­ vey, i.Le. e. See,Ecc, the complete sampiesample of 150 best suited for MOS are in each cluster. tractedtraeted spectra in about two hours. To clusters will be used to initiate a number In this way we decide the optimal posi-posi­ tion angle of the rotator for including as many spectra as possible on the CCDeeo frame. Mask preparation with PUMA has proved to be quite simple. After some Galaxy 4-84-B inin AC-22AC-ZZ practicing we decided to use quite short slitietsslitlets (10 arcsec) to guarantee flexibility during the initial selection of slit posi-posi­ !! tions. This small size allows the spectra !! to be packed more c10selyclosely to each other if desired, while on the other hand longer slits can be built by simply over­over- lapping many slitlets. This isis much sim­sim- pler than the standard procedure involv~involv- ing the construction of a different IHAP table for each chosen slit length. A deci­deci- sion on the best length can then be taken direetlydirectly on the specificspecifie area. There is always a compromise between the desire to observe as many objectsobjeets as possible and the neeessitynecessity to perform a gooogood sky subtraction, and this com­com- promise is obviously dependent on the surface distribution of objects and on 4 ,5 ,G ,7 their magnitudes. Figure 3 shows the WavelengthWav~l~"g~1t (A/IO'l(A/103) MOS frame for AC-22. Figure 4: Spectrum of the 18-magnitudetB-magnitude cD galaxy inin AC-22 (z =- 0.1071). Note the goodgoOO To increase our global effieieneyefficiency and quality of0' sky subtraction and the number of0' absorption features. Total exposure timelimo in this reduce the time necessaryneeessary to complete case is 30 minutes.minules. 47 of parallel studies. We intend to study: References 'Kaiser, N.: 1984, Astrophys. J. (Letters), 284, (a) the luminosity function of cluster L9. galaxies (we have bb, magnitudes from Abell, G.O.: 1958, Astrophys. J. Suppl., 3, Mazure, A,,A, Katgert, P., Rhee, G., Dubath, P., j 211. the EDSGC) and its relations with the Focardi, P., Gerbal, D., Giuricin, G., Jones, Abell, G.O., Corwin, H. H.G.G. and Olowin R. P.: B., Lefevre, 0.,O., Moles, M.: 1989, The dynamical state of the parent cluster; (b) 1989, Astrophys. J. Suppl., 70, 1. Messenger, 57, 30. velocity dispersions and substructure in Bahcall, N.N.A.:A: 1988, Ann. Rev. Astron. & As-As­ Nichol, R.R.C.,C., Collins, C.A,C.A., Guzzo, L., Lums­Lums- those clusters with a large enough trophys., 26, 631.631 . den, S.: 1990, in preparation. number of redshifts. These are just Bahcall, NAN.A. and Soneira, R. R.M.:M.: 1984, As-As­ Peebles, P.P.J.E.:J. E.: 1980, The Large Scale sosomeme examples of the wealth of scien­scien- trophys. J., 277, 27. Structure of the Universe, Princeton, tific information contained in our cluster Dekel, A.:A: 1989, in proc. Vatican Study Week Princeton University Press. redshift survey. However, the most ex­ex- on Large-Scale Motion in the.the, Universe, Sutherland, W.: 1988, Mon. Not. R. Astr. citing results will probably be those we V.V.C.C. Rubin and G.G.V.V. Coyne eds., Vatican Soc., 234, 159.159. City, Pontificia Academia Scientiarum ­- Tonry, J., Davis, M.: 1979, Astron. J., 84, cannot foresee at present, as it has al­al- J., Princeton University Press. 1511. ways been the case when new large­large- Heydon-Dumbleton, N. H., Collins, C.A,C.A., and White, S.D.M.,S. D. M., Frenk, C.S., Davis, M., and scale redshift surveys have been per­ per- MacGillivray, H.T.: 1989, Mon. Not. R. Efstathiou, G.: 1987, Astrophys. J., 313, formed. Astr. Soc., 238, 379. 505.

Comet Austin Rounds the Sun R. M. WEST, ESO

Modern astronomers are privileged umbrellas at hornehome and got wet when ing sky from the roof of my horne home in people. They exert a profession which you predicted sunny weather? And why, Munich in late April this year. for many is also their hobby; they re­ re- yes why did you astronomer "experts" In old days, the appearance of com­com- ceive good support from the authorities; say that the comet would become so ets was always unexpected and it often they have the attention of a broad public bright that it could be seen with the brought fear to monarchs and other rul­rul- and they work in a field which in virtually naked eye, and then I could hardly find ers - no doubt that such events were all respects is above political and that weak patch of nebulosity in my new often cleverly interpreted by sly coun­coun- ecological concerns. expensive telescope, specially bought sellors to their own advantage. These It even appears that they no longer for this "unique" event? times have passed and in our days the run the risk of being punished when they I do not blame the public reaction, for discovery of a new comet, especially make imprecise predictions...predictions . . . As-As­ I have had this experience myself in one in a near-parabolic orbit and there­there- tronomers nowadays only rarely think of early 1974 when I tried to locate Comet fore "new" in the sense that it has never their pitiful eastern colleagues who long Kohoutek from a bai balconycony in brightly Iit lit before been near to the Sun, rather agaago forgot to predict an eclipse and Geneva where I Iivedlived at that time. And I makes some astronomers worry about promptly lost their jobs, heads and lives. had a feeling of "deja vu" when I how accurate their brightness predic­ predic- Of course, in the meantime the com­com- searched for Comet Austin in the morn- tions will turn out to be. putations needed to establish the exact time and place of a solar eclipse one hundred years from now have become so accurate that tour organizers may safely start the preparations and book Komet Rust in ~1989~~1 the hotels already now. On the basis of the collective experience gained during several centuries we now master celes­celes- tial mechanics to a very high degree of 4 M perfection and Voyager was guided to within a few kilometres of the aiming SM point at Neptune, more than 4000 mil­mil- lion kilometres away. M 6

Comet Brightness Prediction: M A Difficult Art 7 M But such a high degree of perfection 8 * is less evident when we turn to the ++ brightness of comets. Indeed, in this M .p-++ field we astronomers have several times 9 been in situations similar to those fre­ fre- P quently experienced by our exposed '--+--f----l--l---I---I--+---l-I--41--1-1--Il---+I.c::·!·-+I--l-I--41-'---;' meteorological colleagues, especially 18.12.1B.12. J.7.1.1.7.1. J.6.2.1.6.2. 18.3. J.7.4.1.7.4. before the advent of remote-sensing 19891984 I1 19901490 weather satellites. Why, demanded the Figure 1:1: Heliocentric brightness evolution of GametComet Austin, showing the rapid decrease after angry public, why did we leave our perihelion. Prepared by Andreas Kammerer (Karlsruhe, Fed. Rep. Germany).

48 Figure 2: GometComet Austin, observed on April 20, 1990 by Michael JägerJager Figure 3: GometComet Austin, near the Andromeda Nebufa, Nebula, photographed (Fischamend, Austria). The impressive tail measures more than 4.5 on April 24, 1990 by Stefan Binnewies (Bochum, F. R. Germany) degrees. Exposure time 4 min on Kodak TP 241524 15 emulsion. 5-min exposure on Agfachrome 1000 RS.

The problem is particularly intricate when it was ideally suited for observa­ observa- there will be more in the coma, and the when the new comet, as was the case tions from the Northern Hemisphere. comet will be brighter. We do not know for Kohoutek and Austin, is discovered The heliocentric brightness change (i.(i.e.e. yet why some comets are more "dusty" while it is still quite far from the Sun and the brightness the comet would have at than others; it could be areala real difference already appears unusually bright at this 1 A. U. geocentric distance) is shown in in composition, or it could simply be that distance. Then the temptation is great to Figure 1.I. An asymmetry around the in sosomeme comet nuclei, the dust "pock­"pock- make a simple extrapolation and to pre­pre- perihelion is clearly visible - the bright­bright- ets" happen to be nearer the surface dict that the comet will become a really ness falls more rapidly off after the and therefore more readily replenish the bright object near perihelperihelion.ion. perihelion. coma via "dust jets". There are probably two reasons for Whatever the reason, it is clear that this. First, several of the "new" comets we cannot with confidence predict a Why Was Comet Austin Not So discovered during the past decades comet's brightness without knowing the Bright? have been unusually bright at large size, structure and composition of its When Austin was discovered in early heliocentric distances, possibly be­be- nucleus in some detail. For periodical December 1989, more than four months cause there were small deposites of var­var- comets, experience has taught us that before perihelion, it was weilwell outside the ious ices (H(H,O,2 0, G0GO2,2 , ...... )) on the surface they behave more or less the same way orbit of Mars, and already of magnitude of their "dirty snowball" nucleus. This at each return and that straightforward 11. This is unusually bright at this dis­dis- layer evaporates alalreadyready at large dis­dis- extrapolations are reasonably secure, tance. If it would behave like most tance and forms a temporarily dense as was the case with GometComet Halley in periodical comets, it could be expected coma around the nucleus. But the de­de- 1986. But "new" comets are also new to to reach magnitude 0 near perihelperihelionion in posites are soon exhausted and then us, and we have no observational early April; indeed, the brightness in­ in- the coma becomes thinner and more means to study their nuclei in detail. For crease in December and most of Janu­Janu- diffuse, and the brightness stalls. the time being, we can only treat them in ary seemed to confirm this trend. The The second is the lack of dust in some a statistical way, hoping that they will first doubts arose in February when it comets, and this is probably the most behave "normally". appeared to become rather diffuse and important reason in the case of Gomet Comet However, comets are real individual­individual- in mid-March it was evident that GometComet Austin. The visual brightness of a comet ists, and we must endeavour to base our Austin was falling behind the predicted is largely determined by the amount of brightness estimates on the best pos­pos- brightness. In the end, it stalled around dust in the coma, whichwh ich effectively re­ re- sible observations. In particular, the ap­ap- magnitude 4.5-5.0 at maximum, with flects the infalling sunlight. When more proximate amount of dust can be about magnitude 5 in late April, the time dust comes out of the nucleus, then judged from infrared observations and 49 ures 2 and 3). While thisthis comet may have been another "flop" forfor thethe general public, itit was a good opportunity toto make use of thethe means and methods fromfram thethe Halley campaign. Observations at La Silla beganbegan in late May, when CometGomet Austin crossed thethe celestial equator and again became ac-ac­ cessible from the southern hemisphere. There was too little time to prepare a detailed summary for this Messenger issue, but it is expected to bring more information in one of the next issues. In the meantime we reproduce here one of the first photos (Figure 4) taken with the ESO 1-m Schmidt telescope in early June. We know for sure that a really bright comet will appear again sometime -­ statistically there are about 4 to 5 such objects per century. But we cannot pre- pre­ dict when this will happen ......

A Delicate PostscripturnPostscriptum Maybe we astronomersastranomers should learn to better resist the pressure of those media who want sensations. When we make an - admittedly not very accurate! - prediction of a comet's maximum brightness, say, as magnitude 0 ±f 2, Figure 4: GometComet Austin is here seen on a 10-min B exposure (lIa-O(Ila-0 + 66385),66 385), obtained by many journalists have a built-in tenden­tenden- Guido Pizarro with the 1-m ESO Schmidt on June 5.39, and photographically enhanced by cy to overlook the plus-sign; it is a safe Hans-Hermann Heyer, ESO-Garching. OfOfparticularparticular interest is the so-called "neck-fine" "neck-line" struc­struc- bet that you will read in the press that ture which is seen as a 1.5-arcmin wide, straight dense structure, stretching at least 2.6 the comet is expected to reach "-2''-2 mag degrees (to the plate border) within a broader, diffuse and rather faint envelope. A much or possibly brighter"brighter,, and become as weaker sunward spike can be followed in the opposite direction to about 30 arcmin distance bright as the brightest planets. And from the nucleus. Both features represent sunlight reflected in dust particles ejected from the comet, and are visible when the Earth crosses through the comet's orbital plane. They were when the comet after all only reaches predicted by M. Fulle (Trieste) and L. Pansecchi (Bologna) in April 1990 (lAU(IAU GircularCircular 4991). The magnitude 2, then we are asked why we insertinserf shows the region around the nucleus. were off by 4 magnitudesmagnitudes...... we ought to take such measurements comet with a fine tail and a good study we ought to take such measurements Acknowledgements more into account in the future. object for both professional and amateur astranomers.astronomers. Many photomet­photomet- I am grateful to Werner GelnikCelnik (Berlin), ric and spectroscopic observations JürgenJiirgen-~inderLinder (Durmersheim), Andreas~ndreks Observations of Comet Austin were performed~erformedwith largelarae telescopes Kammerer (Karlsruhe), Michael JägerJager All of this should not hide the fact that and quite&ite a few amateurs took impres­imp;es- (Fischamend) i is cham end) and Stefan Binnewies~inneies GometComet Austin was still a relatively bright sive photos; two are shown here (Fig- (Bochum) for informationinformation and photos.

Asteroids: A Key to Understand the Evolution of the Solar System M. 01Dl MART/NO,MARTINO, Osservatorio Astronomico di Torino, Italyltaly M.A.M,A. BARUCCI,BARUCCI, Observatoire de Paris, OAEC,DA EC, Meudon, France M. FULCHIGNONI, Universita "La"La Sapienza", Roma, Italy

1. IntroductionIntroduction thethe terrestrialterrestrial planets fram from thethe jovian tionaltional influence influence of thethe massive proto­proto- Asteroids are believed toto be remnantremnant ones. There thethe planetary formation pro­pro- Jupiter. planetesimals framfrom thethe crucial period of cess was interrupted at an intermediateintermediate Asteroid eccentricities and inclina­ inclina- planetary formation and are mostly 10­lo- stage owing toto an unknown mechanism, tionstions were pumped up, thereby increas­increas- cated inin thethe transitiontransition region,region, separating prabablyprobably associated with thethe gravita- inging collision velocities, and transforming 50 CCD photometry. Surface albedo v homogeneity isis estimated on thethe basis of three-three- or eight-colour photometry; m --12.80 1 2m80 8 Sep 3,1986 chemical composition of thethe surface materials isis deduced comparing thethe IR rn• B00 reflectance spectra of asteroids with 0 , 0 thosethose of different materials (meteorites, I 0.8.. O 0 '. lunar and terrestrial rocks, etc.) obtained • 8 0 • .• • in the laboratory, while significant con-con­ • 0 tributions to the knowledge of the phys-phys­ -13.0013.00 ical properties of these materials have - a.• 0 been obtained by radiometry and • • 0 • polarimetry and on the basis of the few • available radar observations. Star occul-occul­ tations and speckle interferometry give • • 0 better data on asteroid shapes and pole orientation, but these measurements f-13.20- 13.20 • are difficult and only few data are pres-pres­ • ently available.available. • • • 0 • • • • 2. Current Knowledge • • • 2.12. 1 Rotation --13.40 13.40 rCfIlM • Asteroid magnitudes vary periodically as they spin, mostly because of •• changes in cross section for nonspheri-nonspheri­ •. cal bodies but also because of surface albedo variations and scattering a • albedo variations and scattering • anomalies. Amplitudes are typically 0.1 -13.60- 13.60 h to 0.3 mag but can exceed 1 mag. To 77h 8 9 1plo U.T.u.T.(~.c)(n.e) date, there are about 4500 numbered I I ~I ~ I minor planets, and we know the rotation Figure 1:1 : Composite lightcurve of asteroid 1188 Gothlandia obtained on September 2-3, 1986 periods of about 600 objects, but the with the 1-m telescope at La Silla. The obtained rotational synodic period is 3.493 ±i- 0.07 rotation data set for the smaller objects hours and the lightcurve amplitude 0.67 ±f 0.01 mag. is very incomplete when compared with (.)(m) Sep 2; (e) Sep 3, 1986. Open symbols are repeated points. the rotation periods available for as­ as- teroids larger than 100 km. In fact, only less than 10% of objects with diameter smaller than 50 km have been observed the accretion among planetesimals intointo elongated or even binary), and in solar and have a well-determined rotation collisional destruction and erosion. Im­Im- system location. Most of them should period, while the percentage isis pacts have altered asteroid sizes, phys­phys- be constituted of essentially unalterated 30-40 % for objects of about 100 km, icalical structures and rotation rates over primitive material in which is preserved and Gloseclose to 110000 % for asteroids largerlarger the course of solar system history; how­how- important information about the chemi­chemi- than 200 km. It follows that special ever, the magnitude of these changes is cal composition and the environmental efforts should be made to enlarge the not yet weilwell understood. Collisional conditions of the protoplanetary nebula available set for the smaller asteroids. comminution among the asteroids con­con- and the processes that produced the The first lightcurve of a minor planet tinues to the present. planetary bodies: asteroids would rep­rep- was obtained in 1901 of 433 Eros, and in Asteroids comprise a great diversity resent the lastlast remnant of the swarm of the next years lightlight variations were ob­ob- of objects, with wide variations in planetesimals which formed the terres­terres- served for several other asteroids, at mineralogy, in size (sub-km to 950 km in trial planets. first by unreliable photographic photom­photom- diameter), in spin rate (a(a few hours toto Even thoughthough asteroids remain points etry which was replaced in thethe 1950s by twotwo months), in shape (spherical toto of light through ground-based tele­ tele- photoelectric photometry. In general, scopes, thethe knowledge of these small we can assert thatthat asteroids are irregu­irregu- bodies has considerably improved over larlar bodies, partially spotted by albedo thethe lastlast twentytwenty years, but the asteroid features.features. However, thethe contribution of Editor's note: This paper isis published inin population isis still poorly known with re­ re- thisthis second characteristic is very small responseresponse toto arequesta request fromfrom thethe ESO Ob­Ob- spect toto thethe other bodies of thethe solar when compared toto thethe variation of thethe serving Programmes Committee.Committee, whose system which have been explored by projected shape during rotation. Light­Light- members suggested that an overview of spacecraft. Ground-based observations curves dominated by shape exhibit twotwo current theories of asteroid formation,formation, provide thethe only available information. maxima and twotwo minima per period (see(see etc. should be prepared. We are thankfulthankful Most of the current knowledge on as­as- Fig. 1)I)forfor obvious geometrical reasons. thatthat Drs. Di Martino.Martino, Barucci and Fulchi­Fulchi- teroidteroid rotationalrotational properties (rotation (rotation Variability due solely toto albedo features gnoni have taken on thisthis tasktask and feelfeel sure that many readersreaders of thethe Messenger period and pole direction) and on their can yield any number of maxima per will appreciate thisthis conciseconcise summarysummary of shapes is deduced by analysing thethe am­am- period, but most commonly one. When minor planet work. plitude and thethe behaviour of thethe light­light- thethe lightcurvelightcurve isis dominated by albedo curves obtained by photoelectric and variegations itit isis possible toto have ambi-

51 guity in determining thethe rotation period needed toto determine itsits shape and pole al., 1985), methods combiningeombining epochsepoehs (Zappala et al., 1983). A fewfew asteroid direction.direetion. MuchMueh work has been carriedearried of extrema and amplitude-aspectamplitude-aspeet rela-rela­ lightcurvelighteurve amplitudes are tootoo small toto out toto determine these parameters from tionstions (Magnusson, 1983; forfor a review of reveal reliable rotation periods. thethe observed light variations, also by pole determination methods, see Mag-Mag­ Plotting thethe available asteroid rotation comparingeomparing the observations with nusson, 1989). The method based on rates versus theirtheir diameter by a so-so­ laboratorylaboratory simulations thatthat help in thethe lightcurvelighteurve amplitude as a functionfunetion of calledealled "running box" technique,teehnique, thatthat understanding how eacheaeh parameter thethe position of thethe asteroid in its orbit was first used for asteroid rotation rates (shape, orientation and surfacesurfaee mor-mor­ (amplitude-magnitude method) has al-al­ by Dermott et al. (1984), there appears phology) influencesinfluenees the lightcurvelighteurve (Ostro ready given spin axis directionsdireetions for to be an increaseinerease in the rotation rates for and Connelly, 1984; BarucciBarueei et al., about 30 asteroids with a good accu-aeeu­ very large objects,objeets, relative to the smaller 1989). racy.raey. The amplitude-magnitude (AM) ones (see Fig. 2). It is as if the marked BarucciBarueei et al. (1989) analysed as-as­ method canean be applied when completeeomplete change in the rotation-diameter dis-dis­ teroids with known rotation periods by lightcurves,lighteurves, obtained during at least 3 tribution at sizes of about I00100 km may means of Fourier analysis of all light-light­ different oppositions, are available. In separate primordial asteroids (right) curveseurves published before 1985. They this way we canean obtain a rough estimate from their collisionaleollisional productsproduets (left). A used a samplesampie of about one hundred of the pole direction:direetion: the larger the possible trend towards more rapid rota-rota­ "best observed" objectsobjeets to discussdiseuss their number of lightcurveslighteurves at different eclip-eelip­ tion rates is present among the very shape distribution. The samplesampie was tictie longitudes, the more accurate is the small asteroids, but there is also an ex-ex­ subdivided in four categories:eategories: 32%32 % of determination. AstrometricAstrometrie and specklespeekle cesseess of slowly rotating objectsobjeets below a the selectedseleeted asteroids have been interferometry methods are in principleprineiple size of about 50 km (this is evident in the classifiedelassified as more or less elongated more accurate, but are also more figure from the increaseinerease in the disper-disper­ ellipsoids, 25 % irregular, 23 % difficultdiffieult to apply and have resulted in sion for the lower size range), and the spheroids and 20%20 % as objectsobjeets probably about ten additional determinations up distribution of rotation rates among the characterizedeharaeterized by albedo features. to now. smallest asteroids is distinctlydistinetly bimodal. The number of asteroids with known Unfortunately, for these objectsobjeets the re-re­ pole directionsdireetions is too smallsmall to perform 2.3 Pole OirectionDirection sults are only indicativeindieative because,beeause, as al-al­ conclusiveeonelusive statisticalstatistieal studies, but from a ready noted, they are affectedaffeeted by the The methods for pole determination preliminary analysis there seems to be a incompletenessineompleteness of the data set. canean be summarized as follows:foliows: photo-photo­ distinctdistinet bimodality in the pole directiondireetion metricmetrie astrometry (Taylor, 1979), am-am­ distribution (Fig. 3). plitude-aspeetplitude-aspect and/or magnitude-as­magnitude-as- The determination of the pole diree­direc- 2.2 Shape peetpect relation (Zappala et al., 1983), tiontion of asteroids should lead to a better We have some indieationsindications on asteroid speeklespeckle interferometry (Drummond et understanding of the role of the eolli-colli- silhouettes that eancan be derived from star oeeultations,occultations, whieh which give the eross-see­cross-sec- tions of asteroids in the plane perpen­ perpen- dieulardicular to the line of sight. Although this 4 result is aspeetaspect dependent, star oeeulta­occulta- tions (Millis and Dunham, 1989) indieateindicate ~ that larger asteroids have either a spher­spher- " ,I iealical or an ellipsoidal shape, while radar , ~, ! delay-Doppler images of smsmallall asteroids I ,.... 1'11\ ' •.• " \~/ (Ostro, 1989) show more irregular "'lI I. f 1/ "" I' , ~ 3.2 " 1, \' • I "'I shapes. On the hypothesis that the as­as- " ,,,J' '.. / teroids evolved eollisionally collisionally from o --. I " planetesimal swarms, these observa­ observa- > Cl> tions eancan be easily interpreted:interpreted: the 0:: largest bodies (D ~> 200 km) are the \J remnants of the original population >. 11 \ ' eharaeterized by equilibrium figures, ~ 2.4 characterized by equilibrium figures, " while deereasingdecreasing the size inereasesincreases the Cl> :::l " number of irregularlyirregularly shaped asteroids, C" affeetedaffected or produeedproduced by disruptive eolli­colli- ...Cl> sions. This interpretation is eonfirmed confirmed -.... ,­ by thethe most reeentrecent results fromfrom experi­experi- o " mental studies of eatastrophiecatastrophic fragmen­fragmen- 0:: 1.6 tationtation processes (Fujiwara et al., 1989, CapaeeioniCapaccioni et al., 1986). The images of thethe smaller bodies of thethe solar system (satellites of Mars and minimoons of Jupiter, Saturn and Uranus), obtained during spaee space mis­ mis- 1 1.5 2 2.5 sions, show thatthat elongated shapes are eommoncommon inin thethe size rangerange 20 toto 200 km. LLog.09. diameter For thisthis reason,reason, bi- and triaxial ellipsoids Figure 2: Plot of rotationalrotational frequencyfrequency versusversus loglog diameter forfor all asteroids with known rotationalrotational seem toto be a realistierealistic approximation of period, excluding the planet-crossing objects and members of the major dynamical families. thethe shape of most asteroids. TheThe "running-box""running-box" containedcontained n = N/10N/IO asteroids (N(N isis thethe totaltotal number of objects inin thethe sampie)sample) The lighteurvelightcurve of an asteroid eon­con- and was steppedstepped throughthrough thethe population one asteroid at a time over thethe entire diameter range.range. stitutes thethe primary observational data One-sigma uncertainties are shown above and below the mean (dashed(dashed lines).lines).

52 majormajor taxonomictaxonomie types,types, namelynamely B,B, E,E, G,G, enstatiteenstatite chondriteschondrites (M).(M). TheThe EE asteroidsasteroids I C,C, M,M, D,D, S,8, V,V, AA andand interpretedinterpreted thethe linkslinks maymay bebe composedcomposed byby thethe silicatessilicates RetrogradeRetrograde II ProgradePrograde betweenbetween thethe classesclasses inin termsterms ofof geneticgenetic formedformed whenwhen enstatiteenstatite chondriticchondritic bodiesbodies rotationrotation 1I rotationrotation 44 trends.trends. ToTo understandunderstand betterbetter theirtheir possi-possi­ (M)(M) werewere differentiated.differentiated. I bleble evolution,evolution, theythey comparedcompared thethe as-as­ TheThe thirdthird andand fourthfourth trendstrends endingending atat I 125 teroidteroid classesclasses withwith somesome meteoritemeteorite VV andand AA classes,classes, respectively,respectively, seemseem toto I samples.sampies. representrepresent lineslines ofof increasingincreasing differentia-differentia­ 129 InIn Figure 44 thethe classesclasses are reportedreported inin tion,tion, startingstarting fromfrom thethe undifferentiated a diagram wherewhere fourfour trendstrends are distin-distin­ material D. TheThe thirdthird trendtrend connectsconnects thethe guishedguished by thethe arrowsarrows thatthat leaveleave fromfrom D D class (through a subunitsubunit of S8 as-as­ asteroidsasteroids (dark objectsobjects withwith veryvery redred teroids)teroids) toto thethe VV class whosewhose end mem-mem­ spectraspectra suggestingsuggesting thethe presence ofof low-low­ bers are coveredcovered by basaltic material temperaturetemperature organicorganic compoundscompounds and (4(4 Vesta)Vesta) and olivinelpyroxeneolivine/pyroxene richrich ma-ma­ typicaltypical of thethe Trojan group) supposed toto terialsterials (349(349 Dembowska and 192 be primitive objects which have under-under­ Nausikaa). The fourthfourth trendtrend connects gone littlelittle or nor heating. Each arrow thethe primitive D cluster toto thethe A unit and goes towardstowards an "end"end class" and itsits contains most of thethe S8 asteroids, whose direction generally indicates a decrease spectra show bands due toto silicates. inin heliocentric distance. The A asteroids show inin theirtheir spectrum The firstfirst trendtrend linkslinks togethertogether thethe D an olivine absorption band that may rep-rep­ cluster with thethe B one, including thethe C resent the signature of mantle material 90"90° 45"45° 25'25° -8'-8° +8"+8° 25'25° 45"45° 90"90° class (probably similar in composition toto of a differentiated body. Bßo 0 carbonaceous chondritic meteorites). In thethe asteroid population a great di-di­ Figure 3: Distribution ofot pole eclipticecliptie latitudes This trendtrend might be interpretedinterpreted inin termsterms versity of albedos is present. Account-Account­ (Po)(ßo) fortor 27 main-belt asteroids whose pole of volatile contentcontent reduction. According ing for the observational biases, about direetion has been determined with good direction has been determined with good to this interpretation, the class D sam-sam­ 75%75 % of the asteroids are found to be accuracy.aeeuraey. Shaded boxes indicateindieate objectsobjeets plespies are richer in volatiles, while the B's very dark, with average albedo of about larger than 200 km. are the poorest due to higher formation 0.3 (D, C, and B types), another group of temperature. objects presents an albedo of about The second trend, connecting the D 0.15 (S,(8, E, M, and V types), few as-as­ to the E class through G and M, may be teroids lie in between, while some bright sional processes in shaping the physical interpreted as a progressive evolution of bodies have albedos up to 0.40 or more. characters of the population: a distribu-distribu­ the solar nebula condensates (D) to-to­ Very interesting is the fact that, in tion with a preferential orientation would wards the enstatite achondritesaChondrites (E) general, different taxonomictaxonomie types are record the initial state of the axis inclina­inclina- through an ultraprimitive, high-carbon, located at different heliocentric distan-distan­ tions, while a random distribution would low-metamorphic-grade C-type mineral ces. This compositional gradient is in­in- indicate a complete reorientation of the assemblage (G) and a reduction (tran­ (tran- terpreted as a "portrait" of the solar spin axes due to the prevalence of colli­colli- sition metal free) silicate similar to the nebula matter, which condensed into sions.

2.4 Taxonomy and Composition The chemical composition of as­ as- teroids is of great interest because the teroids is of great interest because the low volatile different mineralogical assemblages pristine materials may give interesting clues to the under­under- Bl~BO standing of the primordial processes • I" thatthat tooktook place inin thethe solar nebula and -82 during thethe early stages of thethe accretion. / The principal source of information -B3 about composition comes fromfrom spectral analysis of reflected sunlight, although other techniques like polarimetry, radiometryradiometry and radarradar havehave yielded im­im- portantportant contributions.contributions. ManyMany taxonomietaxonomic classificationsclassifications have have beenbeen developed in thethe lastlast decade (for(for a review,review, see see Tholen, 1989),1989), aiming at understandingunderstanding some of thethe physicalphysical and compositionalcompositional propertiesproperties ofof thethe asteroidasteroid basalts pyroxene population.population. TwoTwo recentrecent worksworks areare basedbased & onon multivariatemultivariate statisticalstatistical analysisanalysis ofof as­as- olivine-rich teroidsteroids forfor which which a a homogeneous homogeneous set set ofof spectrophotometricspectrophotometric data,data, from from ul­ul- AO traviolettraviolet toto infrared,infrared, areare availableavailable (Tho­(Tho- - olivine-rich len,len, 1984;1984; Barucci Barucci etet al., al., 1987,1987, whichwhich completecomplete thethe datadata set set with with IRA8IRAS al­al- FigureFigure 4:4: DiagramDiagram showingshowing the the evolutionary evolutionary eompositional compositional trends trends ot of asteroids. asteroids. TheThe arrowsarrows bedos).bedos). BarucciBarucci etet al.al. analysedanalysed 442442 as­as- leaveleave tromfrom D-typeD-type objeetsobjects supposedsupposed toto bebe primitiveprimitive objeetsobjects whiehwhich havehave undergoneundergone littlelittle oror nono teroidsteroids andand inin thisthis samsamplepie identifiedidentified ninenine heating.heating. 53 solid grains first, then formed the ejected in all the directions. We have estimated population of about 1000) planetesimals. This variation in the com­com- then the so-called "dispersed families". have complete lightcurves been ob­ob- position was clearly related to the tem­tem- Finally, the smaller asteroids can be tained. perature decrease with solar distance. It considered single fragments generated is also noteworthy that asteroids be­ be- by catastrophic impact disruptions. 4.2 Distant Asteroids longing to primitive taxonomie taxonomic types Their shapes can be irregular since they (corresponding to least metamorphosed are dominated by solid-state forces and Owing to their great heliocentric dis­dis- material) are present in the outer belt their rotation rate is connected with the tance and their corresponding faintness, regions. partitioning of the angular momentum few observational data have been ob­ob- which occurred during the catastrophic tained on Trojans (a ~5.2-5.2 AU) and on break-up of their parent body (Chapman outer-main-belt asteroids belonging to 3. Collisional Evolution et al., 1989). the Hilda (a ~-44 AU) and Cybele (a and Asteroid Families In conclusion, we can state that most -3.4~ 3.4 AU) groups. These objects are of During the last decade, several of the asteroid population can be con­con- considerable interest because of recent theoretical and statistical articles (Binzel sidered to have been influenced by colli­colli- discoveries, both about their composi­composi- et al., 1988; Davis et al., 1985, 1989; sional processes and the observed dif­dif- tion and the possible evolution of their Farinella et al.al.,, 1981,1981, 1982; Zappala et ferentiations may be due to the physical orbits (Milani and Nobili, 1985). Distant al., 1984) have shown how important the differences of the target asteroids, to asteroids predominantly belong to tax­tax- mutual collisions among asteroids are their varying size and also to the various onomieonomic classes characterized by low al­al- for outlining the evolution of the main impact velocities and geometry. How­How- bedo and red colours, and observational belt following the primordial phases. ever, this description involves some im­im- results from comet nuclei suggest a The outcome of collisions are strongly portant points which must still be better similiar classification (Hartmann et al.al.,, size-dependent, in the sense that the understood, either because of the pres­pres- 1987). To explain the dark, reddish sur­sur- largest asteroids (D 2~ 300 km) appear ence of very severe selection effects in faces of D-type asteroids, which make not to have been strongly affected by the available ground-based observing up more than half of Trojans, Gradie and catastrophic events. In the case of inter­inter- data, or because of discrepancies be­be- Veverka (1980)(1 980) suggested that the spec­spec- mediate size objects (1(10000 s~ D s~ 300) tween the real cases and the results of tra of D-type material can be repro­repro- the largest probable impact energy is laboratory hypervelocity impact experi­ experi- duced by a mixture of silicates with car­car- close to the limits for disruption and for ments (Fujiwara et al., 1989). bonaceous compounds, even more the transfer of a quasi-critical amount of primitive than those found in the car­ car- angular momentum. In this size range is bonaceous chondrites. This is in agree­agree- possible the formation of binaries, tria­tria- 4. Some Open Problems ment with current condensation theories xial equilibrium ellipsoids, and dynami­dynami- about the formation of the solar system 4.1 Apollo-Amor-AtensApo/lo-Amor-Atens (AAA) cal families, i. e. groupings of asteroids and is supported by the spectral studies Asteroids significantly clustered in three orbital of Vilas and Smith (1985), who observed elements: semi-major axis (a), eccen­eccen- Among the small bodies of the solar an increasing reddening of asteroid tricity (e), and inclination (i). In this case, system, the Earth (Apollo and Atens) spectra with heliocentric distance self-gravitation prevents complete dis­dis- and Mars (Amor) crossing asteroid among the Cybele, Hilda and Trojan persion of the target asteroid fragments. population may contain a sm smallall but groups of asteroids. Eight-colour pho­pho- In fact, most of the dispersed mass is meaningful sampiesample of primitive objects. tometry of the outer jovian satellites, at reaccumulated by the mutual gravita­ gravita- The AAA asteroids are generally quite the same heliocentric distance as the tional attraction of the fragments and small, of the order of 5 km in diameter. Trojans, shows however that these ob­ob- the resulting objects may be described The growing number of discoveries of jects are probably mostly C-type. This as a "rubble-pile" or a mega-regolith such objects with large aphelaphelionion distan­distan- "mixing" of C and D types -D- D in the asteroid (Farinella et al., 1981), in which ces and carbonaceous-type reflectance Trojan groups and C in the jovian sys­ sys- rocks from crust, mantle, and core of a spectra strongly suggests that part of tem - poses a complication for the stan­stan- differentiated body have been jumbled them may derive from cometary sources dard formation model of direct correla­ correla- up, thus forming a group of bodies (are they extinct comets?). On the other titionon between asteroid composition and dominated by self-gravitation. Such hand, the AAA with typical diameters of heliocentric distance. The identification bodies, owing to their state of fragmen­fragmen- about 1 km could correspond to a low­low- of D material in the saturnian satellite tation, will relax in hydrostatic equili­ equili- mass tail of the distribution of fragments system and the similarity between the brium figures consistent with their angu­angu- produced in catastrophic collisions continuum spectra of sosomeme old comets lar momentum. which occurred in the main belt and to those of D objects suggest that the If, following the catastrophic impact, then injected into the inner regions of Trojans may not have formed at their the initial velocity of so someme fragments the solar system. present location, but further out, and exceed the escape velocity of the target, Comparison of the properties of com­com- could be related to comets. a few of them may escape, reaching ets and asteroids of the AAA class is For the above-mentioned reasons, heliocentric orbits with elements very complicated by the fact that not much is observations of distant groups of as­as- close to those of the larger remnant. In known about the rotational properties teroids (a ~3 3.25 AU) should be consid­consid- this case an "asymmetrie"asymmetric dynamical and spectra of these asteroids. Photo­ Photo- ered highly important, offering the family" is formed by a large object and a metry and spectroscopy of these ob­ob- possibility to collect data on objects small tail of a few minor asteroids. When jects is difficult since they are faint and quite different from the main-belt popu­popu- the target mass decreases, the proba­ proba- in favourable positions for observation lation. bility to obtain dynamical families in­ in- during a short time only. Some interest­interest- creases significantly. In this case the ing insight into their origins could be 5. Conclusions families are not only formed by the obtained through a more complete asymmetrieasymmetric tail of high-velocity frag-frag­ rotational period data set. Up to now Space missions devoted to the explo­explo- ments originating close to the impact only for about 2020%% of the known AAA ration of small bodies of the solar sys­sys- point, but they are formed by bodies population (about 90 objects out of an tem, such as Vesta, CRAF and Rosetta,

54 or includingincluding asteroid fly-by,fly-by, as Galileo among thesethese thethe most intriguing are: Drummond, J.D.,J. D., Cocke,Coeke, W.W. J.,J., Hege, E.K.,E. K., and Cassini, will give a wealth of high-high­ (i)(i) thethe knowledge of physicalphysieal charac-eharae­ Strittmatter, P.A.: 1985, lcarusIcarus 61,61,132. 132. quality data on thethe asteroid population. teristicsteristies and origin of outer main belt Farinella, P., Paolicchi,Paolieehi, P., Zappala, V.: 1981, lcarusIcarus 46, 1114.14. Not a single close-upelose-up picturepieture of a minor and AAAAM asteroids, (ii)(ii) thethe collisionaleollisional Farinella, P., Paolicchi,Paolieehi, P., Zappala, V.: 1982, planet is yet available, but more infor­ evolution of main belt objectsobjeets and the planet is yet available, but more infor- lcarusIcarus 52,52,409. 409. mation on asteroid rotations, shapes, relatedrelated origin of dynamicaldynamieal families.families. Fujiwara, A,,A., Cerroni, P., Davis, D., Ryan, E., poles and compositionaleompositional typestypes would So far ESO has provided toto thethe Euro-Euro­ Di Martino, M., Holsapple, K., Housen, provide interesting clueselues in understand-understand­ pean asteroidal communityeommunity small tele-tele­ K. E.: 1989, in Asteroids 11, R. P. Binzel, T. ing the role of collisionseollisions in producingprodueing the scopesseopes only (ESO 50-cm50-em and I-m,1-m, Gehrels,Gehreis, M.S. Matthews eds., University of observed asteroid belt and more in gen-gen­ BochumBoehum 61-cm,61-em, Danish 1.52-m and Arizona Press, Tucson,Tueson, p. 240. eral in the evolution of the solar system. GPO). But in order to deepen our knowl-knowl­ Gradie, J., Veverka, J.: 1980, Nature 283, Moreover, the data comingeoming from in situ edge on asteroids and to solve, at least 840. Hartmann, W. K., Tholen, D. J., Cruikshank, measurements will be detailed enough partially, the above-mentioned prob-prob­ D.P.: 1987, Icarus69,lcarus 69,33. to elarify the nature and the interrela­ lems, the availability of larger instru­ instru- to clarify the nature and the interrela- Magnusson, P.: 1983, in Asteroids, Comets, tionships between small bodies popula­popula- ments will be neeessary,necessary, in partieular, particular, Meteors, C.4.C.-1. Lagerkvist and H. RiekmanRickman tions, if any. Are somesome of the Earth­Earth- for photometrie,photometric, polarimetriepolarimetric and spec-spee­ eds., Uppsala Universitet, Uppsala, p. 77. crossingerossing asteroids nueleinuclei of dead com-eom­ troscopictroseopie observations. Magnusson, P.: 1989, in Asteroids 11, R. P. ets? Are the meteorites fragments of Asteroids may be "small""smalI" and "near","near", Binzel, T. Gehreis,Gehrels, M.S. Matthews eds., asteroids disrupted by mutual eollisions,collisions, nevertheless they deserve being investi­investi- University of Arizona Press, Tucson,Tueson, or are they the smallest size tail of the gated by means of large teleseopes!telescopes! p.1180.p. 1180. asteroidal size distribution? Are double Milani, A.,A,, Nobili, A.:A,: 1985, Astron. Astrophys. 144,261.144, 261. or multiple systems present among as­as- References Millis, R.L., Elliot, J.L.: 1979, in Asteroids, T. teroids? Millis, R.L., Elliot, J.L.: 1979, teroids? Barueei,Barucci, M.A., Capria, M.M.T.,T., Coradini, A., GehreisGehrels ed., Univ. of Arizona Press, Tue­Tuc- In order to give an answer to these Fulehignoni,Fulchignoni, M.: 1987, Icaruslcarus 72,304.72, 304. son, p. 98. and other questions, while we wait for Barueei,Barucci, M.A., Capria, M.T., Harris, A.W., Ostro, S.J.:S. J.: 1989, inin Asteroids 11, R. P. Binzel, the results of the spaeespace missions, it is Fulehignoni,Fulchignoni, M.: 1989, Icarus,Icarus, 83, 325. T. Gehreis,Gehrels, M.S. Matthews eds., University neeessarynecessary to improveimprove the number and Binzel, R. P.: 1988, Icaruslcarus 73, 303. of Arizona Press, Tueson,Tucson, p. 1920. quality of data on asteroids: unbiased Capaeeioni,Capaccioni, F., Cerroni, P., Coradini, M., Di Ostro, S.J., Connelly, R.: 1984, Icaruslcarus 57, and detailed Earth-based surveys, ISOIS0 Martino, M., Farinella, P., Flamini, E., Mar­Mar- 443. telli, G., Paolieehi,Paolicchi, P., Smith, P.N., Wood­Wood- orbiting observatory results and Spaee Space Taylor, R. R.C.:C.: 1979, inin Asteroids, T. GehreisGehrels ward, A.,A,, Zappala, V.: 1986,1986, Icaruslcarus 66,487.66,487. Teleseope inputs will be the main sour­ ed.,ed., Univ.Univ. ofof Arizona Press,Press,Tueson, Tucson, p.p. 480. Telescope inputs will be the main sour- Chapman, C.C.R.,R., Paolieehi,Paolicchi, P.,P., Zappala, V., Tholen, D.J.: 1984, PhD Thesis, Univ. of ees of the future data. Embedded in the Tholen, D. J.: 1984, PhD Thesis, Univ. of ces of the future data. Embedded in the Binzel,Binzel, R.R.P.,P., Bell, Bell, J.J.F.:F.: 1989,1989, inin Asteroids Arizona. asteroid beltbelt maymay bebe thethe eluesclues that will 11,11, R.R.P.P. Binzel,Binzel, T. Gehreis,Gehrels, M.M.S.S. MatthewsMatthews Tholen, D.J.:D. J.: 1989, 1989, inin Asteroidsll,Asteroids 11, R.P.R. P. Bin­Bin- helphelp usus toto unravelunravel thethe strueturestructure of thethe eds.,eds., UniversityUniversity ofof Arizona Press,Press, Tueson,Tucson, zel,zel, T. Gehreis,Gehrels, M.S.M.S. MatthewsMatthews eds.,eds., Uni­Uni- early solar system, toto learnlearn about thethe p.386.p. 386. versityversity ofof Arizona Press,Press, Tueson,Tucson, p.p. 1139.1139. planetesimalsplanetesimals and their evolution, and toto Davis,Davis, D.D. R.,R., Weidenschilling, S. J., Farinella,Farinella, ViVilas,las, F.,F., Smith, B.:B.: 1985,1985, Icaruslcarus 64, 503. 503. fathomfathom thethe rneehanismmechanism byby whiehwhich planet­planet- P.,P., Paolieehi,Paolicchi, P.,P., Binzel,Binzel, R.R.P.:P.: 1989,1989, inin As­As- Zappala,Zappala, V.,V., DiDi Martino,Martino, M.,M., Caeeiatori, Cacciatori, S.: S.: buildingbuilding waswas halted halted inin thisthis partpart of of our our teroidsteroids 11,11, R.R.P.P. Binzel,Binzel, T.T. Gehreis,Gehrels, M. M.S.S. 1983,1983, Icaruslcarus 56,56,319. 319. MatthewsMatthews eds.,eds., UniversityUniversity ofof ArizonaArizona planetaryplanetary system.system. Zappala,Zappala, V.,V., DiDi Martino,Martino, M.,M., Farinella,Farinella,P., P., Pao­Pao- Press,Press, Tueson,Tucson, p.p. 805.805. licchi, P.: 1983, in Asteorids, Comets, ThanksThanks toto thethe ESOESO faeilities,facilities, espeeial­especial- lieehi, P.: 1983, in Asteorids, Comets, Davis,Davis, D.D. R.,R., Chapman,Chapman, C.C. R.,R., Weidenschil­Weidenschil- Meteors,Meteors, C.-1.C.4. LagerkvistLagerkvist andand H.H. RiekmanRickman Iy in the last five years, a lot of data, both ly in the last five years, a lot of data, both ling,ling, S.J.,S.J., Greenberg,Greenberg, R.:R.: 1985,1985, Icaruslcarus 62,62, eds.,eds., UppsalaUppsala Universitet,Universitet, Uppsala,Uppsala, p.p. 73.73. physiealphysical andand astrometrie,astrometric, werewere obtainedobtained 30.30. Zappala,Zappala, V.,V., Farinella,Farinella, P.,P., Knezevi6,Kneievic, Z.,Z., Pao­Pao- onon asteroids.asteroids. Nevertheless, Nevertheless, manymany un­un- Dermott,Dermott, S.S. F.,F., Harris,Harris, A.A. W.,W., Murray,Murray, C.C.D.:D.: lieehi,licchi, P.:P.: 1984,1984, Icaruslcarus 59,59,261. 261. solvedsolved problemsproblems stillstill remain remain openopen and and 1984,1984, Icaruslcarus 57,57,14. 14.

TheThe DustDust TailTail ofof CometComet WilsonWilson 1987VII1987VII G.G. CREMONESE,CREMONESE,Osservatorio OsservatorioAstronomico,Astronomico, Padova,Padova, Italyltaly M.M. FULLE,FULLE, OsservatorioOsservatorioAstronomico,Astronomico, Trieste,Trieste,Italy ltaly

1.1. IntroductionIntroduction andand 68426842 toto studystudy thethe dustdust environmentenvironment whiehwhich thetheejeetion ejection ofof dustdust isisrestrieted restricted toto SeveralSeveral photographiephotographic plates, plates, bothboth inin ofof C/1987VIICl1987Vllbefore beforeperihel perihelionion by by meansmeans aaeone cone ofof halfhalf widthwidth ww withwith itsits symmetrysymmetry redred andand blueblue light,light, were were obtained obtained by by ofof thethe inverseinverse numeriealnumerical methodmethod whiehwhich axisaxis pointingpointingtoward toward thethe Sun.Sun. TheThe posi­posi- meansmeans ofof thethe ESOESO SehmidtSchmidt eameracamera toto waswas sueeessfuily successfully testedtested onon C/1973XIICl1973Xll tiontion ofof eaeheach graingrain atat thethe observationobservation isis studystudy thethe dustdust andand plasmaplasmatails tails ofof Com­Com- andand C/1962111Cl1962 111 (Fulle,(Fulle,1989). 1989). derivedderived fromfrom itsits kepleriankeplerian motion,motion, thenthen etet WilsonWilson 1987VII.1987V11. AllAll thesethese platesplates werewere ThisThis modelmodel eonsiders considers NtNt xx N~tN, Xx NN,s projeetedprojected into into thethe photographiephotographic planeplane ealibratedcalibrated by by means means ofof ealibrationcalibration samsamplepie dust dust grains, grains, where where NtNt isis thethe eoordinatecoordinate system, system, soso asas toto obtainobtain thethe wedgeswedges andand thereforetherefore areare suitablesuitable forfor aa numbernumberof of samsamplespies in inthe thetime timeinterval intervalof of modelmodel distributiondistribution ofof thethe seatteredscattered light light quantitativequantitative analysisanalysisof of thethe dustdust andand ionion dustdust ejeetion,ejection, NN,tt isisthe the numbernumberof of sam­sam- fromfrom thethetail tail andand thethe relatedrelated kernelkernelmat­ mat- tails.tails. The The pass-bandpass-band ofof thethe emulsion­emulsion- piesplesin inthe thesizes,' sizes,and andN N,s isisthe thenumber numberof of rixrix A.A. TheThe solutions solutions areare givengiven by by the the filterfilter eombinationcombination ofof redred plates plates is is fromfrom grainsgrains of of aa fixedfixed sizesize uniformlyuniformly distri­distri- minimizationminimization ofof thethe funetionalfunctional [AF-W[AF-112+ + 630630to to700 700nm, nm,close closeto tothe theR Rphotomet­ photomet- butedbutedon ona adust dustshell. shell.It Iteonsiders considersdiffer­ differ- ß~~[BFI*,[BFf, wherewhere A A isisthe the kernelkernelmatrix, matrix, IIis is rieric system.system. WeWe usedused platesplates 6810,681 0, 68296829 entent ejeetion ejection geometries geometries for for eaeh each ofof thethe datadata veetorvector eontaining containing thethe dustdust tailtail 55 Plate Time UT r L'.A o.u. Exp. Emulsion 8SIOB10B RR~kysky - - 6810 Mar 27366 1.26 1.42 43°43" 20 098+RG630098 + RG 630 - - 6829 Apr 2368 1.23 1.24 48°48" 30 098+RG630098+ RG630 91591 5 ±+ 15 20.38 ±+ 0.02 6842 Apr 7348 1.22 1.09 51°51" 30 098+RG630 750 ±+ 20 20.60 ±2 0.04 TABLE 1: PhotographiePhotographic data. Plate, serial number of the photographicphotographie plate. Time UT, time of mid-exposure. r, LI,A, 5un-GometSun-Comet and Earth-GometEarth-Comet distaneesdistances (AU). 0:,a, Phase angle. Exp., exposure time (minutes). Emulsion, emulsion and filter eombination.combination. 5Slos,1OB, sky background surfaeesurface fightlight 2 intensity expressed in number of 10 R-magnitude stars per square degree. RRsky,sky, sky background R-magnitude aresee-arcsec-? .

surface light intensities of the NNkk images sampled in NN x NM points, B is a reg­reg- ularizing matrix weighted by ß,p, and F is the solution vector sampled in N,Nt x N,,Nu values, from which the dust number and ... o mass loss rates and the time dependent ~o;;;0 and time averaged size distributions can >0 be directly computed. Contrarily, the dust ejection velocity v(t) is required for dust ejection velocity v(t) is required for L~,=:_::HL~~w= ~~U~=~-~1/~6~~~V~~~90~-u u~u~=,~-~1/~,6~~~w~=~45~~J the computation of the matrix A, so that 180 -0.20 -0.10 000 -0.20 -0 10 000 -020 -0.10 000 it must be determined by means of a trial and error procedure. The regulariz­regulariz- ing weight ß[3 tunes the constraints to our ill-posed problem: when ß(3 increases, ..,", ;:; the instability of F decreases, but also the quality of the fit to the data. There­There- ... fore, the most probable dust velocity v(t) o ~o o is defined as the function giving a stable ;;;0 o o > 0 (~~\ ;r·(~ and positive vector F for a regularizing weight ßfi as small as possible. -~~ 1 u=-1/4 w':;180 u=-1/4 w= 90 u=-1~4 w= 45 ~~~~, ' ~~,~~ , -0.20 -0.10-0 10 0000 00 -0.20 -0.10 0.00 -020 -0.10 0000 00 2. Data Reduction Figure 1:1 : Isophoteslsophotes of the dust tai!tail from image 6810 for the intensity levels 1.6, 2.4, 3.8 and 8.7 The plates were digitized adopting expressed in sky surfaeesurface intensity units. The distaneesdistances along the axes are expressed in 10lo66 km square scanning windows of 50 [tmym22 units. Gontinuous Continuous fines: lines: observed isophotes. Dashed fines: lines: eomputedcomputed isophotes. w is the and the photographiephotographic densities were anisotropy parameter. u = blag6 log v(t, d)/bd)/6 log d (Table 2). transformed into intensity by means of the related calibration wedges. To per­per- form the absolute calibration of the im­im- ages, we selected three photometrie photometric our pass-band and the R photometriephotometric verse problem. In Table 2 we show the fields from the first edition of the new system. parameters associated with the applica­applica- Guide Star Photometrie Photometric Catalogue tion of our method to the images of CIC/ (GSPC-I, Lasker, Sturch et al., 1988). 1987VII.1987V11. For each parameter combina­combina- 3. Results Such fields were digitized by means of a tion, we tested the number of trial veloc­veloc- square scanning window of 20 [tmym22 and In Figure 1 we show the comparison ity functions v(t) given in the table. The were linearized by means of the same between input image 6810 and the re­re- solutions concerning the dust ejection calibration wedges used for the comet construction of the same image by velocities, the range of diameters of the images. For each GSPC-I star of visual means of the solution F, which allows to considered samsamplepie grains, the dust loss magnitude V, we obtained the red mag­mag- test the accuracy of the solution itself rates and the power index of the time­time- nitude R following Johnson (1966)(1 966) and and the stability of our constrained in- dependent size distribution are shown in measured the integrated intensity over a sky area covering the whole star trail and over a same area of sky back­back- ground near the star trail, obtaining the w N~l N~l M sky background surface light intensity u w NsNs NLt Nt Nt N!, NkNk NivlNM NN T M 8S S10BSI0, expressed in number of 10 R-mag­R-mag- -1/6-116 180°180" 284 100 100 20 10 3 30 30 8 4.4 0 nitude stars per square degree (Table 1). -1/6 90°90" 143 100 100 20 10 3 30 30 27 3.3 0 The very small errors affecting the sky -1/6-116 45°45" 382 100 100 20 10 3 30 30 10 1.9 6A intensities refer to the fits to the mea­mea- -1/4-114 180°180" 284 100 100 20 10 3 30 30 12 6.0 + sured star intensities, and not to sys­sys- -1/4-114 90°90" 143 100 100 20 10 3 30 30 9 5.4 x tematic errors, which may weilwell be larger -1/4-114 45°45" 382 100 100 20 10 3 30 30 31 2.7 *-X and may have been introduced by the TABLE 2: Parameters of the model of GametComet Wi!son.Wilson. u = blag6 log v(t, d)/bd)/a log d. w, half width of reciprocity effect of the plates (the expo­expo- the dust ejeetionejection eone:cone: isotropieisotropic ejeetionejection (half width of n), hemispheriealhemispherical ejeetionsejections (half width of sure times of the stars and of the comet n/2),?r/2), and strongly anisotropieanisotropic ejeetionsejections (half width of n/4).d4). N,,Ns , N,,,NI" N,,Nt, dust sampiessamples on a dust were obviously different, since the com­com- shell, in the modified size and in time. N,,Nt, N,,,N", sampiessamples of the solution in time and in the modified et image is fixed, whereas the stars are size. NM, NN'NN, sampiessamples of the NNkk soureesource images in the M and N direetions.directions. T, number of test 14 trailed) and by the differences between funetionsfunctions v(t). M, total ejeetedejected dust mass (10(loi4grams) for Ap(u)Ap(o:) = 0.02.5,0.02. S, symbol in Fig. 2. 56 Figure 2. The dust loss rates were com­com- puted adopting the albedo Ap(a)Ap(u) = 0.02 8 (Hanner and Newburn, 1989,43°1989,43" < a < o 51°, phase angle a in Table 1).I). The slow increase of the dust number loss rate is mostly due to the decreasing size interval whwhichich was considered. The mass loss rate related to isotropieisotropic dust ejections shows a wide maximum at t =- -120- 120 (days related to perihelion), that is "CD'" "" at r =-- 2.4 AU, whereas the mass loss 2['-"" rate related to strongly anisotropieanisotropic ejec­ejec- tions is about constant. Large uncertain­uncertain- "'"'<0'" '"h ties of the loss rates are due to the g;u) poorly known albedo of large grains. 000000000 '" 000 8 The loss rates shown in Figure 2 are 00°000 I I 00 inversely proportional to the assumed ~C\l 0 00 0 0 0 0 0 0 B~ ~ ~+ *,,~I!J ~ll value of Ap(a). The uncertainties of the I 000 "0[') ~ ~ ~ ~ ~ ~ 00+0~ dust bulk density are much less impor­impor- h '"' 0 0 0 0 0'0 .8 I U n I!l i1d'l iIJ l1l U Q EjJ :v I 00 :vi 0 "Q + J< ~ ~ tatant.nt. In fact the mass loss rate com­com- ..,..J "'" Lf') 06. . 8 I "=-_~_~_~_~----' & I ~~---='c~---c'=~---c'=~---c'=co----c'=co----'=~ puted by means of dust tail analysis is '" _L5c'-c3~2-_~2~8~7 -179 -120 ·-83 -58 -38 -532 -287 -179 -120 -83 -58 -38 independent of the dust density (Fulle, '0* time (days related to perihelion) time (days related to perihelion)

1989), whereas the number loss rate is Figure 2: Dust environment of Comet Wilson 1987VII1987Vll assuming the albedo Ap(n)Ap(a) = 0.02: the directly proportional to the square of dust lassloss rates (depending inverselyoninversely on Ap(ol)l,Ap(a)), the dust ejeetionejection velocity, the power index of dust density. For plates exposed to the the time-dependent size distribution and the diameter interval to whiehwhich all the solutions are red pass-band, the contamination by related. The symbols are related to Table 2. The time sampling steps eorrespond correspond to true plasma (H(H20c)2 0+) is a concern along the anomaly steps of 5°.54 prolonged radius vector. This is re­ re- flected in the residual instability of the solutions for t>t > -60, which explains averaged size distribution, charac­ charac- tronet Trieste centre. The diagrams the large dispersion of the mass loss terized by the very high power index of were generated using Astronet AGL rates and of the power index of the size -3.0 ±f- 0.1. These results show that the standard graphics. We thank P. O.D. Usher distribution. However, plasma contami­contami- dust loss of Comet Wilson 1987VII1987V11 was for useful discussions concerning the nation to the left-hand side of the tails is already significant at r =-- 7 AU, a Sun­Sun- plate calibration. This work has been very improbable, so that forfür t < --6060 the Comet distance even larger than that supported by a PSN/CNRPSNICNR grant to Prof. solutions should be free of significant observed for Comet Kohoutek C. Barbier!.Barbieri. errors. (r = 5 AU). At these distances the gas We find that C/1987VIICl1987Vll produced production should be dominated by 6 more than 10lo69g S-1S-' of dust during two COC02,2 , and we observe also a maximum References years before perihelperihelion,ion, and this may be of the dust mass loss rate and a fast Fulle, M., 1989, Astron. Astrophys. 217, 283. related to its high relative luminosity at increase of the dust ejection velocity Johnson, H. H.L.,L., 1966, Annual Review Astron. the first observations. Our results sug­sug- when the sublimation of HH2020 becomes Astrophys. 4, 193. gest that the mass loss rate does not efficient. Lasker, B. B.M.,M., C. C.R.R. Sturch, C. Lopez, A.D.A. D. increase close to perihelperihelion,ion, in agree­agree- Mallama, S.S.F.F. McLaughlin, J.J.L.L. Russeli,Russell, W.Z. Wisniewsky, B.A. Gillespie, H. Jenk­Jenk- ment with the results of Hanner and Acknowledgements ner, E.E.D.D. Siciliano, D. Kenny, J. J.H.H. Newburn (1989). The power index of the - Newburn (1989). The power index of the Baumert, A.M.A. M. Goldberg, G.G.W.W. Henry, E. size distribution shows smsmallall variations. The plates were digitized by means of Kemper and M.J. Siegel 1988, Astrophys. We find that its value is higher than -4, the POSPDS of the Padova Astronomical J.J, Suppt.suppi, Seroser,68, 1. and this implies the release of very large Observatory. The calculations were per­per- Hanner, M. M.s.,S., and R.R.L.L. Newburn, 1989, As-As­ grains. This fact is confirmed by the time formed on the Apollo computers of As- tron. J. 97, 254.

Chiron's Blue Coma R. M. WEST, ESO

The Most Distant Minor Planet Chiron was discovered in late 1977 by At the time of its discovery, Chiron Known Charles Kowal of the Palomar Observa­Observa- was classified as a "minor planet", and it tory. He found a slow-moving, 18-mag was obvious that it must be a very large Among the nearly 4500 minor planets object on plates taken with the Palomar one, in order to be so bright at this large which have been numbered until now, Schmidt telescope and within a few distance. OependingDepending on its ability to re­re- (2060) Chiron is by far the most distant weeks, enough positions had been flectfleet sunlight (albedo), the diameter was and certainly one of the most unusual. It measured to compute a preliminary or­or- estimated as somewhere between 100 moves in a rather eccentric orbit be­ be- bit. It was later identified on other photo­photo- and 250 kilometres. Kowal and other tween the giant planets Saturn and graphiegraphic plates dating back to 1895, and minor planet specialists feitfelt that Chiron Uranus and each revolution lasts just soon the unique nature of Chiron was might be the first of a new family of over 50 years. firmly established. minor planets, and it was inofficially de- 57 confirmed the presence of this coma (IAU(lAU Circular 4947).

Observations at ESOE$O During fourlour nights in late February this year, I had the opportunity to observe Chiron and its newly discovered coma with a CCD camera at the Danish 1.5-m telescopetelescape at La Silla. My main object of study, Comet Halley, was tootao low in the sky toto be observed during the first hour of the night and I therefore took this opportunity to point the telescope to-to­ wards Chiron. Both objects have a very faintlaint coma around a point-likepoinHike light source, but while the magnitude of Halley's nucleus was only 24-25, Chi­Chi- ron was much brighter, about 16.5 in the visual range. It was thereforetherelore necessary to restrict the integration time to a fewlew minutes in order to avoid overexposing (saturating) the image of01 Chiron with the undesirable side-effects of01 photometricphotometrie non-linearity and column "bleeding"."bleeding~. In all, about three hours of exposure was obtained in the two standard col-col­ ours B (4000-4800 A) and V (5000-S800(5000-5800 A). The cleaning of the frames was quite laborious, in particular because of the rather large number 01of pixels with deviating sensitivity on this FiguraFigure 1:1 : False-colourFalse-c%ur reproduclionreproduction of Chiron's eomacoma in visua/llght.visual light. The field size is 70 x 70 CCD chip (ESO No. 15). The sky aresec:arcsec; North is up and EastEsst is to the left/eft. GalacticGa/aetie stars have been removed fromtram this picture, background was also rather "dirty":"dirty~: whiehwhich is a composite of 20 frames with a total integration time ofo( 107 min. The outer isophote corresponds to a surfaeesurface brightness of V -27.5 maglarcsecmag/arcsec?2. there were comparatively strongstrang inter­inter- ferencelerence fringes in the V-band, most like-like­ Iyly due to the exceptional strength of the atmospheric oxygen line at 5577A,5577 A, at this time near solar maximum activity. cided that other members of this class a magnitude more than predicted (lAU(IAU Adding the frames in the V-band pro-pro­ would also be given the names of Circular 4554). This trend continued and duced thethe false-colourlalse-colour image repro-repro­ mythological Centaurs, half man and by the end of 1988, Chiron was almost duced here (Fig. 1),I), for the first time half animal likelike Chiron itself. However, one magnitude brighter than it ought to showing the large extent of the Chiron despite various search programmes, be. coma and allowing a more detailed notably by Kowal at Palomar, no other No other minor planet is known to study 01of its morphology. We see first of members of this dassclass have beenboon found have behaved this way and thelhe idea was all that it is elliptically shaped with thethe until now, though some of the minor soon put forward that ChiranChiron is actually major axis in NW-SE direction. It11 can be satellites 01of the outer planets may pos­pos- a comet, i.e.Le. a body consisting of ice followedlollowed to about 20 arcseconds from sibly be captured objects which are and dust, rather than a minor planet of Chiron where the surface brightness is 2 physically similar to Chiron. solid rock. Some astronomers also near 28 mag/arcsecond2,mag/arcsecond , i.i.e.e. -7- 7 mag, thought of a minor planet whose surfacesur/ace or over 600 times, fainter than thethe sky is partly covered by a layer 01of ices. A emission in the V-band (Fig. 2). Minor Planet Or Comet? natural explanation of the brightness in-in­ What may be even more interesting is The firstlirst years after itsits discovery, Chi­Chi- crease would then be the sublimation of that the colour of this coma is rather ron looked like a minor planet and be­be- ices from the sur/ace,surface, leading to the blue; at 5S arcseconds fromIrom the centre, haved like one. Slowly moving towards creation of a "coma","coma~, a surrounding (B-V) = 0.3 ±+ 0.1, and it looks as if the its perihelperihelionion --whichwhich it will reach in early c10udcloud of icy particles and possibly also coma reddens slightly outwards to February 1996 at heliocentric distance samesome dust, released in the same pro­pro- about (B-V) =- 0.45 at 12 arcsecond 8.48 A. U. - its brightness rose gradually cess. Such a coma would reflect the distance. The colour of Chiron itself was through the 1980's,19801s, exactly at the rate sunlight and thereby increase the ob­ob- measured in the early 1980's as (B-V) = predicted for an inert body which shines served brightness. 0.70 +± 0.02, Le.i.e. near the solar value by sunlight rellectedreflected fromlram its surface.sur/ace. A coma was indeed seen around Chi­Chi- (0.65) and typical for aC-typea C-type minor However, in 1988 aastrange strange phe­phe- ron in early 1989 by Karen MoosMees and planet (see also the article by di Martino nomenon was observed. Comparing Michael Belton with the KittKilt Peak 4-m et al. in this Messenger issue on with observations from 1986, D.J. Tho-Tho­ telescope (lAU(IAU Circular 4770). It11 had the page 50). Thus the coma is significantly len and his collaborators working at the form of a 5-arcsecond, very weak exten­exten- bluer than the surface of Chiron. This is NASA Infrared TelescapeTelescope on Hawaii sion towards southeast. Further obser-obser­ also confirmed, when thethe predicledpredicted light noticed that Chiron suddenly appeared vations with thelhe Canada-France Hawaii contribution fromIrom Chiron itself is sub­sub- to have brightened by several tenths 01of Telescope by Karen Mees in early 1990 tracted Iromfrom the central condensation of

58 20,----,------, "spirals" in the coma, leaves the impres­impres- sion that the evaporation occurs over a I \ CHIRON/V SURFACE BRIGHTNESS larger surface area, rather than from iso­iso- I lated vents, like those detected on the nucleus of Halley. It can be seen (Fig. 1) that the innermost part of the coma is ~ 23 somewhat asymmetrically placed with u(/) respect to the nucleus. The direction of 0::: this elongation does not coincide with « the direction to the Sun or the direction o of orbital motion, both vectors being ~ near West (p.(p.a.a. = 269269"0 and 289°,28g0, re­re- <.) spectively). ~ 26 It is in principle possible that this asymmetry is connected to the direction of the rotation axis, the projection of which might be perpendicular to the di­di- rection of inner coma elongation. Since the evaporation from the surface is likely 29 "------'-- ..l------'- ----.J 291 I I I to be strongest during the "Chiron after­after- 5 10 15 noon", just after the most intensive solar heating at "noon""noon",, the direction of rota­rota- ARCSEC tion would appear to be from NW to SE, as seen projected onto the sky. How­ Figure 2: Mean radial luminosity profile in V of Chiron's coma, after subtraction of the as seen projected onto the sky. How- contribution from Chiron itself. The abscissa indicates the distance from the centre in ever, it should not be forgotten that even arcseconds (1 arcsec = 7680 kilometres projected); the ordinate is the surface brightness in the inner coma features are still at sever­sever- magnitudes per square arcsecond. The corresponding sky background emission is -21~21 mag/ al arcseconds' distance from the centre 2 arcsecarcsec.?.. of light, i.i.e.e. more than 20,000 km from Chiron's surface. They may therefore not be directly connected to phenome­phenome- na on or just above the surface. light; the remaining image, which is pre­pre- possible to be more specific about the nature of these particles, their size dis­ sumably that of the coma cloud immedi­immedi- nature of these particles, their size dis- Future Investigations ately surrounding Chiron, is also blue, tribution, chemical composition and (B-V) = 0.4 ±k 0.1. density. Details ababoutout these new observations The blue colour of the coma is most of Chiron's coma will be reported in a Iikelylikely due to the scattering of the sun­sun- forthcoming paper in Astronomy & As-As­ Chiron's Rotation light by small particles. The possible trophysics. They pose a number of inter­inter- reddening outward can be explained by By careful measurement of the bright­bright- esting questions which can only be an­an- the destruction of the smallest particles ness of the central condensation, it was swered byaby a more detailed investigation. as they drift away from Chiron, so that possible to confirm the light variation For instance, it would be most desirable the relative content of larger particles noted earlier by Bus et al. (lcarus,(Icarus, 77, to perform photometry of the coma in increases outwards. This is therefore in p. 223, 1989), on the basis of CCD mea­mea- other wavebands, also in the infrared general agreement with the idea that the surements in 1986 and 1988. Thanks to region. Apparently, no gaseous emis­ emis- coma is caused by the sublimation of the longer time interval, the period of sions lines have been observed so far in ices on the surface, a process that ap­ap- this variation, i.i.e.e. the rotation period, the spectrum of Chiron, but it may weilwell parently started when Chiron's inward­inward- can now be estimated with higher accu­accu- be that a gaseous component of the bound orbital motion brought it within racy: P = 5.91783 ±i= 0.00005 hours. coma can be detected at a later time. -~ 12 A.A.U. U. of the Sun. The absence of any significant, night­night- There is little doubt that Chiron will be It will of course be necessary to study to-night changes in the coma structure, a popular target for solar system as­ as- the coma in more wavebands before it is and the lack of evidence of "jets" or tronomers during the coming years.

New Communication Link Between GarehingGarching and La Silla A. WALLANDER, ESO

1.lntroduction1, Introduction (ND).(NW. Although the physical distance both in technological and scientific In the beginning of February a new between Garehing Garching and La Silla will al­al- areas. permanent communication link between ways be the same,same: the new communica­communica- La Silla and Garehing Garching have al alreadyready ESO Headquarters and observatory tion link will make the logical distance been linked on a permanent basis for came into operation. This new 64 kbps between people working in Europe and several years via an analogue leased digital link will, among other things, be­be- South America smaller. It will contribute line. Astronomers and engineers have come the backbone for remote control to a higher level of integration of the become accustomed to call up col­col- of the New Technology Telescope organization increasing the productivity leagues on the other side of the Atlantic 59 mote controlcontrol andand generalgeneral communica-communica­ tionstions call forfor a system which integrates GARCHING LA SILLA data, voice and video image communi-communi­ cations. Depending on thethe typetype of oper-oper­ ation, different users should be given access toto thethe link.link. The system should be Voice Voice "future"future compatible" inin thethe sense thatthat new users should be easy to integrate, Satellite hardware should support a future higher videoVideo videoVideo bandwidth link and the system should image .:.'...H I';image codec image image codec TDM TDM be adaptable to new technologies. High reliability and availability should be Data -1 ,/ 64 kbps \ 1------7Data guaranteed through the use of redun-redun­ dancy and powerful monitoring and diagnostic functions. These are very ambitious requirements, especially when considering the limited trunk Supervisor Supervisor when considering the limited trunk bandwidth of 64 kbps.

3. System Architecture Figure 1:1 : System Architecture. The integration of many users has been implemented by means of time division multiplexing (TOM).(TDM). This tech­tech- simply by dialling a special prefix vices Digital Network), fast packet nique allows the 64 kbps trunk to be spit number. Many e-mail and fax messages switching and other upcoming tech­tech- up intointo smaller bandwidth user pass over this lineline every day. The CAT or nologies. To appreciate the difficulties, channels. The method of time division the 2.2-m telescope is controlled from one has to consider the different impliesimplies that the sum of the user Europe around 12 nights every month characteristics of these types of com­com- channels bandwidth isis less less than the using thisthis leasedleased line.line. The new link will, munications. Voice and video are analo­analo- trunktrunk bandwidth. The allocation of at leastleast forfor thethe timetime being,being, bebe a comple­comple- gue inin naturenature and need toto be digitized bandwidthbandwidth isis done from from a supervisor supervisor mentment toto thesethese well-established com­com- before using digital transmission media.media. terminalterminal connectedconnected toto thethe TOMTDM micro­ micro- municationmunication facilities. In In bothboth casescases thethe Voice and video transmissions are also processor.processor. Reconfiguration Reconfiguration can bebe linkslinks are leasedleased fromfrom thethe German and sensitivesensitive toto delays, but not so fuzzy mademade fromfrom one sideside on-line or via pre­pre- Chilean PTT'sPTT's and are using Intelsat lntelsat about correctness. The opposite isis truetrue programmedprogrammed configurations activated at communicationcommunication satellites.satellites. forfor digital data transmission, transmission, where a defined timetime of day. The system is is WhenWhen discussingdiscussing long-distance long-distance com­com- correctnesscorrectness is is a a must, must, but but reasonable reasonable extendableextendable inin thethe sensesense thatthat newnew usersusers municationmunication links, links, the the mostmost importantimportant delaysdelays areare notnot soso critical.critical. (input(input channels)channels) cancan bebe addedadded byby plugplug inin characteristiccharacteristic is is bandwidthbandwidth oror thethe TheThe combinedcombined requirementsrequirements of of re-re- modules.modules. The The system system also also allows allows for for amountamount of of information information whichwhich cancan bebe transmittedtransmitted withinwithin a a timetime interval.interval. TheThe newnew digital digital link link has has five five times times higher higher capacity to transmit raw digital informa­ i"'TRS' capacity to transmit raw digital informa- A&A tiontion comparedcompared toto thethe analogueanalogue linklink andand i r.+!==_======1==1 thisthis toto onlyonly aa 2020 %% higherhigher cost.cost. ThisThis isis inin lineline withwith thethe presentpresent trendtrend inin internation­internation- Bridge alal communicationcommunication tariffing,tariffing, whereby whereby costcost forfor higherhigher bandwidthbandwidth digitaldigital leasedleased lineslines isis decreasing.decreasing.

2.2. RequirementsRequirements ExperienceExperience withwith the the existingexisting remote remote observingobserving facilities facilities for for thethe CATCAT andand 2.2-m2.2-m telescopes telescopes hashas shownshown thethe needneed totointegrate integrate voice,voice, datadata andand videovideo imageimage Router communications.communications. Experience Experience with with thethe a analogueanalogue line line hashas also also shownshown thethe im­ im- portanceportance ofof allowingallowing moremore generalgeneralcom­ com- 2.2m municationsmunications during during day day timetime whenwhen no no telescopestelescopes areare remotelyremotely controlled. controlled. In In fact,fact, oneone couldcould argueargue thatthat this this second second pointpoint is is more more important important since since remote remote controlcontrol always always will will bebe usedused less less than than ---- =-cop copperper cablecable 5050%% ofof thethe time.time. =-- = duplexduplexfiber fibercable cable IntegrationIntegration ofof voice,voice, data data and and video video ======redundant redundant fiberfibercable cable imageimage communicationcommunication has has been been a a hot hot OTOT ==optical o~ticaltransceivertransceiver topictopic forfor somesometime time andand isisaddressed addressed inin developmentsdevelopments likelikeISDN ISDN(Integrated (IntegratedSer- Ser- FigureFigure2: 2:ESO ESO WideWideArea Area Network.Network. 60 duplicationduplication of of processor processor board board andand powerpower supply supply with with automatic automatic switch switch overover inin casecase ofof failure.failure.

3.13.1 VoiceVoice ToTo implementimplement meaningfulmeaningful voicevoice con­con- necHonsnections thethe telephonetelephone exchangesexchanges (PBX)(PBX) alat thethe twotwo sitessites needneed toto bebe con­con- nected.nected.This Thisallows allowsany any extensionextension atat oneone sitesite calling calling anyany extensionextension atat thethe olherother sitesiteusing usingaprefix a prefix numbernumberto toaccess access thethe exlemalexternal tietie line.line. ThatThat isis exactlyexactly thethe wayway thethe presentpresent Hetie lineline conneclionconnection overover thethe analogueanalogue linklink works.works. However, However, inin orderorder toto interfaceinterface toto thethe TOM,TDM, thethe analogueanalogue voicevoice signalsignal firstfirst hashas toto bebe digitized.digitized. TheThe commoncommon methodmethod10 to digitizedigitize voicevoice isis10 touse usepulse pulse codecode modulationmodulation (PGM).(PCM). TheTheanalogue analoguevoice voice signalsignal isis sampledsampled atat 80008000 HzHz andand eacheach samsamplepie isis codedcoded inin 88 bits,bits, thusthus a a bandwidthbandwidth ofof 6464 kbpskbps isis requiredrequired forfor oneone voice voice channel.channel. UsingUsing thisthis methodmethod obviouslyobviously isis badbad economyeconomy overover thethe newnew digitaldigital linklink (remember(remember thethe initialinitial statement statement thatthat this this lineline hashas fivefive timestimes thethe capacitycapacity oltheof the analogueanalogue line).line). DifferentDifferent types types of of delta delta modulation, modulation, wherewhere thethe differencedifference betweenbetweentwo two sam­sam- piesples isis codedcoded instead instead of of thethe absoluteabsolute value,value, improvesimproves thethe situationsituation and and thethe samesamevoice voice qualityquality cancan bebe obtainedobtained us­us- inging onlyonly 3232 kbps.kbps. ByBy usingusing parametricparametric codingcoding insleadinsteadof of waveformwaveform coding,coding, itit isis possiblepossible toto lurtherfurther decrease decrease thethe necessarynecessary bandwidth.bandwidth. ThisThis requiresrequires moremore compJex complex signalsignal processingprocessing andand powerfulpowerful hardware.hardware. With With present present tech­tech- nologynology itit isis notnot possiblepossible toto maintainmaintainthe the samesame voicevoice qualityquality whenwhen goinggoing downdown inin availableavailable locallylocally at at the the telescopes.telescopes. about 10 seconds. In medium resolution bandwidth.bandwidth. TheThe mainmain questionquestion isis if if thethe Therefore,Therefore, aa video video imageimage transmissiontransmission mode this figure is reduced by a factor voicevoice quality quality using using this this method method isis systemsystem isis required.required. OneOne couldcould also think of two. acceptableacceptableto tothe the users.users. ofof otherother applications,applications, likelike some type 01of A preliminary version of01 this system GonsideringConsideringthe the needneed toto shareshare thethe 6464 videovideo conferencing,conferencing, where suchsuch a sys­sys- was used during the NDNlT inauguration kbpskbpstrunk trunk betweenbetweenmany many users,users, itit waswas temtem could could be be useful.useful. However, However, when to transmit images fromlrom the auditorium decideddecided toto installinstall slate-of-the-artstate-of-the-art voicevoice consideringconsidering the the enormousenormous informationinformation inin Garching to La Silla. codecscodecs usingusing onlyonly 2.42.4 kbps.kbps. ThusThus itit contentscontents in in a a video video signal and the would in principle be possible to have limited bandwidth available, com- would in principle be possible to have limiled bandwidth available, com­ 3.3 Data 2626 suchsuch voice voice channelschannels overover thethe link.link. pramisespromises havehave toto bebe soughl.sought. A full mo­mo- TwoTwo such such voicevoice codecs codecs havehave beenbeen in­in- tiontion digitized digitized video video signalsignal rsquires requires a OataData communication for remote con-con­ stalledstalled and and werewere takentaken into into operation operation bandwidlhbandwidth ofof hundredshundreds of Mbps.Mbps. By us­us- trol of the GATCAT and the 2.2-m telescopetelescope afteraftersome someinitial initialinterfacing interfacingproblems problemsto to inging advancedadvanced compressioncompression algorithms it isis based on a point-to-point connectionconneclion thethe PBXPBX atat LaLa SillaSilla werewere rapidlyrapidly solvedsolved isis however however possiblepossible toto transmittransmit lowerlower betweenbetween the remote contral control computer byby LuisLuis Aguila.Aguila. TheThe initialinitial experienceexperience isis resolutionresolution and/orand/or lowerlower refreshrefresh raterate vid­vid- and the instrumentinstrument computer. A similar thatthat thesethese voicevoice channelschannels areare useable.useable. eoeo imagesimages over over aa lower lower bandwidth bandwidth connection has been implemented toto ImprovementsImprovementsare arestill stillpossible possibleas as somesome channel.channel. thethe NDNTT control computer over the new problemsproblems havehave beenbeen identifiedidentified and and AA slowslow scanscan televisiontelevision system has digital link.link. However, this type of con-con­ shouldshouldbe besolved solvedin inthe thenear nearfuture. future.This This beenbeenchosen chosen thatthat operatesoperates eithereither inin high nection does not solve the need for gen-gen­ systemsystem maymay anywayanyway bebe comptementedcomplemented resolutionresolution (576(576 •* 720720 pixels) pixels) oror medium medium erality and connections to other compu-compu­ withwith oneone higher higher quality,quality, higherhigher band­band- resolutionresolution (356'(356 * 576576 pixels)pixels) mode. mode. In In ters. At La Silla there had been thethe wish widthwidth voicevoice channel.channel. Use Use ofof such such a a highhigh resolutionresolution modemode aa video imageimage isis for some time to build up a network voicevoice channelchannel will will however however penalize penalize capturedcaptured andand digitizeddigitized usingusing 1616 bitsbits per connecting the various lelescopestelescopes and otherother usersusers andand cannolcannot bebe availableavailable allall pixelpixel into into 6 6 MbitsMbits 01of data. data. TheseThese data thethe general off-line computers. thethetime. time. areare compressedcompressed 2020 timestimes before trans­trans- InIn close collaboratiun collaboration with people mission.mission. Because Because compression, compression, trans­trans- from La Silla, inin particular Gaetano An-An­ missionmission andand decompressiondecompression areare carriedcarried dreoni, a design was worked out to start 3.23.2 VideoVideoImages Images outout inin parallelparallel andand communicationcommunication over­over- implementingimplementing such a network. The initial TheThe remoteremote observing observing astronomer astronomer headhead isis minimized,minimized, thethe resultingresulting frameframe need was to connect the local area net-nel­ needsneeds toto havehave accessaccess toto TVTV picturespictures refreshrefresh raterate overover aa 4848 kbpskbps channelchannel is is work (LAN)(LAN) of the NDNlT and the general 61 computer LAN in thethe administration wellweil as definition of typetype of access, e.g.e. g. timetime of writing it is normal toto see at leastleast building with the LAN in Garching.Garehing. DueOue a host may be allowed toto send e-mail, one user fromfrom La Silla loggedlogged inin on thethe toto thethe distances at La Silla (diameter but not allowed toto do a remote login main VAX inin Garching.Garehing. It isis fairfair toto say over 3000 m) thethe transmissiontransmission media (TELNET, rlogin).riogin). thatthat thisthis proves thethe usefulness of this had toto be optical fiber. Use of fiber connection and it is expected that the optics also have the advantage of re­ use of thisthis facilityfacility will increaseincrease drastical-drastical­ optics also have the advantage of re- 4. Experience After the First moving problems of earthing and risk for lyIy inin thethe near future.future. moving problems of earthing and risk for Months of Operation damage to equipments during lightning. It should be noted that all installations It was decided to start implementing a In the long term, the availability of the at La Silla have been carried out by local fiber optic Ethernet backbone network. link will become crucial. More and more staff, in particular Gaetano Andreoni, A backbone network only carries traffic users will realize the advantage using Rolando Medina and Luis Aguila. DuringOuring between the connected LAN's, while this communication facility and take for the commissioning phase the communi-communi­ local traffic is contained locally by granted it should be available. At ESO cation system itself was used extensive-extensive­ means of bridges. The hardware com-com­ we can build in redundancy and recov-recov­ ly.Iy. Troubleshooting and integration of ponents were chosen in such a way that ery procedures in our equipment, but new components are facilitated by an new points of interest easily can be inte-inte­ we cannot do anything to guarantee the intense communication via e-mail, file grated by pulling new fibers and instal-instal­ availability of the leased line from PTTs. transfers and telephone conversations. ling new modules. For reliability reasons This situation is very frustrating and it is all fiber links are duplicated with auto­ important to collect statistics and anal-anal­ all fiber links are duplicated with auto- 5. Future Developments maticmatie switch over in case of fiber break-break­ yse fault conditions in this initial phase. age. Fibers have also been chosen to be DuringOuring the first weeks of operation the DuringOuring the coming year work will con-con­ compatible with the next generation downtime of the link was about 30%.30 %. centratecentrate on implementing remote con-con­ LAN called FDDlFOOI (fiber distributed data This terrible figure has improved, but at trol of the NlT.NTT. This application will have interface) running at ten times the speed the time of writing it is still 10%. 10 %. It is priority and other users will have to (I(10000 Mbps). The delicate work of instal-instal­ clear that this is still unacceptable for accept this. Iingling and terminating fibers, using fusion the future, but hopefully the improving However, it is expected that other ap-ap­ splicing technology, was carried out by trend will continue. Good working rela-rela­ plications will also gain in importance. Rolando Medina. tionship with the PTTs has been estab-estab­ For example, it is alreadyal ready planned to The connection between the back-back­ lished and by identifying weak points extend the backbone network at La Silla bone LAN and the TDMTOM is implemented and improving recovery procedures the to other telescopes. New local applica-applica­ using high performance OSI level 3 rout­rout- availability should improve. tions over the backbone network are ers, supporting multi protocols (at pres­pres- OuringDuring the NTTNT inauguration, three expected, e. g. data sharing between te­te- ent only TCP/IP is used). This approach days after the link was available to ESO, lescopes, archiving, centralized infor­ infor- was chosen in preference to remote a preliminary video image transmission mation accessible on-line from the tele­tele- bridges because of performance and system and one voice channel were op­op- scopes (STARCAT, seeing measure­ measure- security reasons. A router gives better erational. The point-to-point connection ments), etc. performance for short interactive to the NTTNlT computer has been used Software development and mainte­ mainte- messages and provides much more extensively for software upgrades and nance, not only for telescope and instru­instru- powerful security and diagnostic troubleshooting during the last months. ment control, but also for MIOASMlDAS and facilities. It will continue to prove to be an impor­impor- other applications, will become much This implementation gives full con­con- tatantnt tool during the integration of EMMIEMMl easier. nectivity between all computers con­con- and later IRSPEC software. The fiber In the long run, the experience and nected to a LAN in GarehingGarching or La Silla optic backbone network at La Silla was know-how gained by using this com­com- using TCP/IP protocol. The routers taken intointo operation and connected to munication link will be an asset for the allow access control on a host basis as GarehingGarching LAN without problems. At the VLVLTT project.

Atmospheric Extinction at La Silla from September to December 1989 N. CRAMER,CRAMER, Observatoire de Geneve, Sauverny, Switzerland

Since November 1975, thethe Geneva The M+OM+D techniquetechnique developed by F. night; otherwise, thethe observations are Observatory photometry group has Rufener (see forfor example a description carried out at a constant air mass and been systematically carrying out mea­ mea- inin Astron. Astrophys. 165, 275-286, thethe reductionreduction isis generally done by using surements in the Geneva 77-colour-colour sys­sys- 1986; or inin lAUIAU Symp. 111, 253-268, thethe mean extinction values of thethe site. temtem at La Silla. Special care has been 1985) allows thethe measurement of thethe OuringDuring thethe reductionsreductions of M + 0D observa­observa- takentaken toto ensure thethe conservation of thethe atmospheric extinction coefficients and tions,tions, however, thethe instantaneousinstantaneous passpassbandsbands and of thethe reductionreduction pro­pro- theirtheir evolution with timetime over thethe dura­dura- monochromatic extinction coefficients cedures over the period of almost 30 titionon of a night of observations. Our ob­ob- corresponding toto thethe mean wavelength years thatthat the the system has been in servers usually apply that technique of each filter are computed throughoutthroughout use. This guarantees thethe long-termlong-term when thethe meteorological conditions are thethe duration of thethe night. homogeneity of thethe data recorded. judgedjudged toto remainremain good during thethe whole Over thethe years, we have frequently 62 been asked by visiting astronomers at Monochromatic Extinction Coefficients (La Silla) at 3464, 4015, 4227, 4476, 5395, 5488, La Silla for these values obtained at 5807 A. given dates. We have therefore offered Date U BiB 1 B B2 ViV 1 V G the editor of the Messenger to publish aUoU aBinB 1 aBnB aB2oB 2 oV1nV 1 oVaV oGaG some of these results in the journal. This should be possible, provided that not 8. 9.89 .6013 .3083 .2509 .2064 .1327 .1355 .1230 too much of the valuable space is taken .0063 .0064 .0057 .0051 .0058 .0046 .0063 up by these data. 14. 9.89 .5909 .2988 .2415 .2032 .1301 .1303 .1186 In the table, which covers the last four .0058 .0064 .0060 .0059 .0064 .0049 .0079 months of 1989, we present in a concise 15. 9.89 .5967 .3095 .2476 .2102 .1338 .1345 .1237 form the mean monochromatic extinc­ extinc- .0075 .0052 .0047 .0050 .0050 .0041 .0067 16. 9.89 .5921 .3007 .2456 .2047 .1272 .1323 .1233 tion coefficients measured by the M + D + .0053 .0059 .0058 .0057 .0059 .0048 .0069 technique during the nights beginning 18. 9.89 .6102 .3168 .2513 .2102 .1373 .1362 .1230 on the given dates. The second line .0047 .0045 .0043 .0058 .0048 .0031 .0081 gives the standard deviations over the 23. 9.89 .6258 .3302 .2666 .2260 .1458 .1493 .1310 variations of each value during the night .0060 .0046 .0046 .0040 .0036 .0022 .0058 and provides a rough estimate of the 24. 9.89 .5893 .3026 .2454 .2060 .1269 .1274 .1180 stability of the transparency at that .0048 .0032 .0027 .0025 .0033 .0010 .0046 time. 25. 9.89 .6092 .3191 .2624 .2230 .1386 .1414 .1278 The frequency of M + D nights in this .0057 .0056 .0058 .0057 .0059 .0050 .0070 27. 9.89 .6194 .3267 .2674 .2225 .1437 .1458 .1321 table is fairly irregular; no attempt .0083 .0050 .0062 .0036 .0040 .0030 .0047 should, however, be made to interpolate 20.10.89 .5958 .3084 .2515 .2107 .1317 .1339 .1227 between non-consecutive nights. Read­Read- .0038 .0037 .0027 .0030 .0019 .0015 .0028 ers who would like to have more de­de- 19.11.89 .6173 .3257 .2663 .2171 .1351 .1337 .1231 tailed information (for example evolution .0047 .0038 .0036 .0040 .0025 .0020 .0036 of the extinction over a given night) may 20.11.89 .6208 .3279 .2690 .2238 .1362 .1368 .1217 contact me. .0036 .0028 .0026 .0026 .0026 .0020 .0041 30.11.89 .5993 .3116 .2507 .2015 .1368 .1287 .1192 .0048 .0028 .0029 .0020 .0025 .0009 .0018 2.12.89 .6061 .3135 .2547 .2131 .1289 .1251 .1184 .0068 .0045 .0050 .0047 .0028 .0027 .0031 3.12.89 .5993 .3030 .2468 .2029 .1255 .1197 .1127 MIDASMemoMlDAS Memo .0075 .0039 .0035 .0035 .0033 .0024 .0032 6.12.89 .5980 .3124 .2491 .2088 .1315 .1265 .1181 .0034 .0027 .0024 .0027 .0030 .0024 .0032 ESO Imagelmage Processing Group 11.12.89 .6945 .3179 .2578 .2111 .1334 .1293 .1209 .0070 .0047 .0042 .0050 .0041 .0039 .0042 21.12.89 .6803 .3777 .3145 .2683 .1697 .1723 .1554 1. Application Developments .0095 .0092 .0090 .0094 .0091 .0088 .0096 22.12.89 .6424 .3484 .2868 .2391 .1535 .1505 .1405 SameSome improvements have been ad­ad- .0138 .0111 .0106 .0098 .0090 .0088 .0096 ded to the applications related to spec­spec- 23.12.89 .6273 .3389 .2770 .2310 .1425 .1436 .1257 troscopy especially in the LONG SLiTSLIT .0084 .0073 .0062 .0061 .0059 .0057 .0073 context. All the commands related to 24.12.89 .7070 .4019 .3353 .2877 .1901 .1905 .1735 the context ECHELLE have now been .0051 .0042 .0041 .0036 .0036 .0032 .0035 ported from the old MIDASMlDAS into the 30.12.89 .7231 .4134 .3446 .2993 .2008 .1969 .1792 90 MAMAYY release and tested on CASPEC .0109 .0079 .0075 .0072 .0068 .0066 .0077 data. 31.12.89 .7005 .3957 .3270 .2823 .1862 .1845 .1698 .0143 .0126 .0113 .0111 A number of irritating problems still .0116 .0108 .0116 exist in many applications either due to unclear documentation or errors in rou­rou- 3. New Positions tines often caused by the conversion to VVWMSI'V

Contents J. M. Beckers: Planning the VLT Interferometer ...... •.... 1 D. Enard: How Will the VLT Mirrors Be Handled? ...... •.•.. 9 F. Merkle et al.: Adaptive Opties at the ESO 3.6-m Telescope ...... 9 F. Merkle: What's Next in Adaptive Opties? 12 S. di Serego Alighieri: The sr-ECF After the Launeh of HST 13 Profile of a Key Programme. D. Reimers: A Wide-Angle Objective Prism Survey for Bright Quasars ...... 13 Profile of a Key Programme. M. Turatto et al.: A Photometrie and Spectros· eopic Study of Supernovae of All Types...... 15 Prolile of a Key Programme. G.F. Bignami et al.: Optical Follow-up Identifica­ tions 01 Hard X·Ray/Soft y-Ray Sources Discovered by the "SIGMA~ Telescope...... 16 H. E. Schwarz: Report on the First ESO/CTIO Workshop: "Bulges of Galaxies" .. 18 News Aboutthe ESO Exhibition ... 18 12th European Regional Astronomy Meeting of the lAU...... 19 New Videos Irom ESO ...... 19 A. Fishburn: European Group of Astronomical Librarians (EGAL) ...... 19 Announcement 01 the 4th ESO/CERN Symposium on "Cosmology and Funda- mental Physics" and the 15th Texas Symposium on "Relativistic Astro- physies" ...... 20 The New Look of the ESO Headquarters 20 lAU WG on PhotographyTo Meet at ESO ...... 21 R. Booth: Stop Press (June 6,1990) -At Last, We Know Where La Silla Is! ... .. 21 Vacancies ...... 21 New ESO Preprints (March-May 1990) ...... 21 Staff Movements ...... 22 Professor J. H. Oort at 90 22 A Blaauw: ESO's Early History, 1953-1975. VII. The late 1960's: Struetural Changes, First Scientific Activities and Some Soul-Searching; the Journal A&A...... 23 L. Pasquini: SN 1990 I in the Polar Ring Galaxy NGC 4650 A...... 34 F. Bresolin, M. Capaccioli and G. Plotto: The Stellar Content of the Dwarf GalaxyNGC3109.. 36 I. Appenzeller and S. Wagner: Probing the Hidden Secrets 01 Seyfert Nuclei ... 40 L. Guzzo et al.: A Redshift Survey of Automatically Selected Clusters of Galaxies ...... 45 R. M. West: Comet Austin Rounds the Sun ...... 48 M. Di Martino, M.A. Barucci and M. Fulchignoni: Asteroids: A Key to Under- stand the Evolution of the Solar System...... 50 G. Cremoneseand M. Fulle: The Dust Tail 01 Comet Wilson 1987 VII 55 R.M. West: Ghiron's Blue Goma. 57 A. Wallander: New Communieation Unk Between Garehing and La Silla ...... 59 N. Cramer: Atmospheric Extinction at La Silla from September to December 1989 . 62 ESO Image Proeessing Group: MIDAS Memo...... 63

64