1964ApJ...140..107M favoring have region boundary. spectral a line interstellar by some stronger ginally strength example CN of would unique, possibility basis (1942, and distant account obtained of discussed grains at emission considered concentration esses in the few © The A It Adams' the this the Dunham structure line, at a group American ionization, has bright when leading the sixty unique sublimation "A are dispersions 1946) be interstellar respect. the detected. since resolving 3874.00 R(O) quantitatively than to It of been same have in of expected also fl.ashed hypothesis material of stars. is it interstellar those nature stars the stars, detail. as (194J) Carnegie would the of obtaining further AN to of of those highly Astronomical realized operating been authors to And, produced the Pleiades the the A embedded interstellar in by CH+ The It of powers on INTERSTELLAR whether employed, absorption is of In was by the interstellar provide from of (0, suggested in that was formation Ca noticed between spectrograms Institution indeed, spectrum, probable CH4 CENTRATION absorption lines this CN by Bates seven UV 0) advanced more n, for established, the actually in Mount stars available in band the by several provided from radiation paper the and appear Society the CN an the molecules. information to that showing 4.5 many observational and stars, two the lines characterized strength emission of molecular of in in atomic that molecules have Wilson show formation observed the or Washington, Received the the the on a interstellar lines Spitzer and investigators stellar particular, obtained I. in due in (Adams • Gurno of hypothesis does 9 interstellar some photochemical CN dispelling the B been unique the INTRODUCTION Provided A/mm. unreddened the ABSTRACT and nebula CN three CLOUD the lines The 2 due to ~+---? of OF arise advancing molecules March about not basis lines radiation. CH (1951) 107 by CH Palomar support the of spectrograms observed lines, their MU-NCH material data. in on to 1943, times CN California near exceedingly in case CH. exceed X molecules At where CN or concentration, should a 5, of by interstellar high-contrast for the 2 the that some solid WITH ~+ galactic interstellar showed the so MOLECULES 1964 a CH+ In are Adams' of Observatories the stars ionization weaker 1949). molecule immediate to the later systellJ, degree reactions strong cluster by a gathered particular, further While 7 the formed particles, NASA Institute Merrill's be doubts group origin strong mA lines of Adams depends A date of scale that regarded The CH+ and types observations NGC of front. CH HIGH as several at in in this have Astrophysics neighborhood more understanding atomic CN of emulsions of uniformity of Bates these by intensity involving the raised is "A the the to strength, suggestion. lines followed and stars 7822 (1949) Technology B2-B5 3874.61 the lines. the a same the to be been solid Pleiades P(l) source as or CON­ hundred observations observation some has CH+ CH+ and lines. outstanding are writer Evidence earlier associated circumstellar. less particles process observed in line with more of been that A, of the while by Spitzer Data comparable of in the spectra the ions, conspicuously extent are the the The stars And as for is of dissociation information the discovered stars the by interstellar their often is only measured H relatively System strongest of the the does studying presented in analysis with relative 11 on highest are of only Merrill the will on (1951) in terms so region proc­ truly mar­ R(l) than very The this not not Hr the the far an be in in of to 1964ApJ...140..107M · casual The The other who with "comet-tails" at dred that trum with 108 stars of of lines embedded cules. lent the values besides and known, involved HD two the have CN (Jenkins (Sp +66°1675 +66°1674 +66°1661 © The the interstellar * The the t R(O) 07, :first CH: CN: 224938 Williams American "comet-tail" spectrograms central absorption quite :fixes indicated width the that diameter near probably at observed star In inspection and very nebular emission Adopted bright Adopted the V and 4.5 number ...... spectrogram order Wooldridge in have line its .... likely (HD the = in of lines by A/mm. part the boundaries evidently HELIOCENTRIC distance 9.05, the a rest rest (1959). of the that Astronomical star around positions absorption been colon additional associated Pc6131 Pc6006 Pb6996 Pc7520 Pc7517 Pc6992 material, to establish PLATE 202124, is we of 171 CN wavelengths: wavelength of appears nebula structure 1937). K-line of thus B HD as Ca+ can a are inspected, in uncertain. this is spectrogram - The as obtained The 15 is ABSORPTION his 80 dealing we 224938 and an -10.8 -17 -18.1 -16.6 -15.0 -15.3 be V of Sp expected CA+ (Mi.inch produced is 900 is X pc, star nebula mean to stars with main lines R(O) catalogue 4300.325 mA = are order the seen RADIAL the also appearing 09.5 260 .2 Society CH The be surrounded pc. +1.09), radial lead~ X ...... has going H -17.6 -16: -21.1 -20.8 -22.0 and likely the in 3874.61 (HD with overlaid spectrogram in source CH* mA for present X in lb, II. Sh171. A. It of and II directions for 4300. velocity with stars been LINES VELOCITIES emission in GUIDO the to that this • THE consists magnitude region, V and and a Sp to A, location . . . . . Wilson R(O) Provided a a in the -17.6 single -14: -19.9 -23.1 of = R(l) R(l) 9.2 Palomar TABLE star consider region found The was B9, and associated Pc6006 by star OBSERVATIONS the of has the excitation IN to 7.80, radial . . X A/mm derived and ...... MUNCH CH heavy since STARS which 3874.00 the nebula proves near V of arc, line been emission ...... Ca+ revealed 1962). was -17.4 -16.6 -17.6 -16.4 along (km/sec) R(O) to with = by B a 1 larger R(l) North X velocities has by Sky given Her pointing show bright that 7 it - doublet briefly 4300 A, dispersion, the NEAR was obscuration, giving . . .30), with of that Shl unusually The P(l) the also ...... V been only -21: -24: -15...... of Survey P(l) NASA X complex Shl71 of than OF the observed by definitely . = 71 is double 3888.65, NGC X at line . . CN central half-weight unquestionably H measurement described +66°1675, shows . . . . . 387S.77 THE CNt only 7 identified + to an has ratio given presence a II ...... in of Astrophysics weight -16.5 . . . . . distance 0, at apparently the P(2) 7822 E-plate arc will . . INTERSTELLAR regions. been . . . . high any of A, sight about 22), . . XX apparently several is region in ...... produced central in with P(2) with the ...... very to be 1.30. the by ...... 3874.61 other Table the published density -14: . . . . . among by respect of P(3) which discussed. of ...... X CN No. half of . Osterbrock radius R(O) The 3876.30, course large of . . . . such roughly two Sharpless . . . . . bright The region, is about . . lines Data the wavelengths star line to 1...... 555. by as BD+66°1675 might -17. -18.8 -16.8 inspection Mean Pc6131. and several taking of well-marked The dimensions. P(3) a and intensity near star much. of absorption by . heretofore region, in System CN rims Only 1° . . A disregarding suggests circular, 7 a X 3874.00, equiva­ a 3876.84 Blanco ...... also survey (1959) (1957) almost 35 is list X -18. -16: place spec­ mole­ Her hun­ 3889 and The well one pc. we of be of in of A 7 1964ApJ...140..107M

@ s> NGC7822 ..,~ ;:;· =~ > "'..... 8 +66° 1675 =0 s.... I') ~ -00 0 +66° 1674 ....I') ~ -< • 1 ~ ca+ K 0 3 < Hel 23s-3 P a: CN RI RO Pl P2? P3~ ~ c::i.. O" '< \~~? f z 00> > s Oph > ::;"' 0 'g. '< ;:;·"' "'~ ~ S" rJ1 '< ;-"' 8

FIG. 1.-The interstellar ab0 sorption lines of CN and K of Ca+ in the spectrum of two stars embedded in the emission nebula Sh171 , near NGC 7822. The original spectro­ grams have a dispersion of 9.2 A/ mm. The lower spectrum is that of r Oph in the region of the CN lines, obtained with the Mount Wilson coude spectrograph at 1.1 A/ mm. 1964ApJ...140..107M of due for shift of place of or more south of, errors 27' to than trogram shown of intensity redward present an ticular to with ess, line filaments have suggests emission are Examples have has emission example lifetimes ing the with reflection where with 1955). the years processes by entering © excitation The The He this these the The settle accidental K a in known, reflection observed south American extended very of and considerably +66°1675 the black in an it the strong I near of same (Bates position no object by sight In 0-type star spectrogram simple is be fact nearly lines, so of emission of that the into measurement, two nebulae, 200-inch the nebula +66°1675, strong of ratios brightest not stars nebulae are this the determining from of discounted. this than 120 body the although +66°1661 association. the been the possibility interstellar for stars question, relationship particular from emission and more dark visible although they complexion Doppler seen Astronomical case, observation star at fainter mA. Orion are angle ! besides +66°1675 +66°1675 molecular molecules. CH Sh171. (IC at discovered, )ess and the it Spitzer coude was nebula associated found the are of nebula (Sharpless +66°1674 lines 10000° however, On is of in and 405) in it Nebula, 287° all adopted i star, than not made Another and shifts (Sp Sun thus the the what when their is with its that those the situations A Its molecular to are CH+ are reflection with between not showing of which 1951). 4.5 true covering absorption K, spectrum, of is from does. reflection 09.5, lifetimes corresponding Society The the reproduced is that further spectrum located encountered. the apparent identification plate appears those given distinctly with has erroneously the of strong it less possible diluted INTERSTELLAR A/mm and obviously is lines. distance any in corresponding spectrogram, might lifetime Ca+ molecules about The measured shows +66°1675. V In a appropriate general, would than grain emission molecular Osterbrock of signs lines. in Stromgren molecular • nebula = basis III. the general, in are The CN nebulae, and Provided to P(1) it the by Table shows spectrogram takes 8.72, by in well the half in areas 200 of seen, appears late DISCUSSION be obliterating be interacting very of of a We interstellar most star!; of P(2) CH Figure the given R(2) as Sh171. is line factor are in (NGC a immediate difficult be one pc. nebulae B a interaction place. its 1. the Its B-type made however, rather absorption the twice have, with case lines. +66°1675, magnitude the account A poorly P-lines sphere conditions - by somehow the There cases 1952; and is spectral and 4300. Oph, CH by highly interstellar spectroscopic CLOUD 1, case V very of the positions Although 7023), of The case uncertain a as shows shows P(3) on Sharpless The to = compact 3 X 3 with R(3) and stars molecule to lines reflection the the NASA Morgan, around known, is where of broad if specify. will neighborhood clearly +0.81) the the star probable locate that little ih surrounding with type unsaturated. and related relation the showing lines 10-u;, Pleiades. R(2) shows. fainter and to surrounding the lines, in p only have reaction other Astrophysics AE of Oph CN the most as star make the only the by it cluster. it question R(O) and with present, precisely of (1959) against It and distance appears Stromgren, spectrum for which Pc7520, upon seems interstellar Aur, which to nebular to the lines In molecular dust than, of HD the is that and hand, strong of three the example, But, line be a the R(3) an of order molecular rates absence the same which of 6-8-hour A associated as 20077 somewhat interest x and The taken agree, both that equivalent photodissociation geometric about HI and should and interaction as at 9.2 will where as the Oph, the modulus stars possible absorption lines Data molecular molecular (Herbig of conspicuously to gas a in possibility material, CN HI and immediately A/mm lines the 5, is stars several Ca+, outstanding be H is of distance in the understand ihn the within the the associated which associated located System cannot lines to surround­ only be along II obtained the exposure band, this distance material Johnson with weaker empha- arise various with region. belong factors reality source case would in width 1958), proc­ spec­ finite dark lines lines with 2000 par­ 109 line also but the the an of as at of 1' of in a 1964ApJ...140..107M . point stars size, dence large Applying kpc spectrogram considered. cedents. coeval. observed The in would plausible ering, Ca+ in velocity net placed be region nebula expanding able observed of 1957), Mlinch, tion the to that than NGC Spitzer ceding tion are ascribe 110 cule ing dently in B-type 1964). NH medium? exposed The © The be this all the the given found CN radial 3 near for lines small American is in concentration , nevertheless, the present embedded would discovered. as at cases and in 7822 grains H further, boundary, appear discussion shifted appear Doppler A direction component. are the an impossibility stars, In its Oort's become (1951) with Flather, to a in favor He II in in in that equality few in and a Observation velocities answer difference distance H20, origin the mostly around observed UV-, region. the It arise the correction favor a be +66°167 the I on removed upon in that originate few other absorption-line to significant, also the Astronomical star may constant of explaining expected that other shifts vanishingly Doppler in which stars and the would X-, the to we Because near and will the displaced could distant of of shift that the Shl of being of somewhat +66°1674 of In the well of emission wish concentrations or once of in grains. the violet this the 5 HI +66°1661 idea two of the be Coffeen 0.7 the exciting six 71 they the for in the in indicates forming ')'-radiation radial be sublimation of the be He (Kraft the for be flashed idea settled shifts dust-rich to with cluster gas the kpc, stars difficulty the stars of the radial when the helpful stars. solar that H Ca+ of obtained put suggested to I Society were the small. The interstellar a the II absorption near laboratory nebulae the stable components velocity presence that the smaller 1959), the Ca+ uniform while the stars, at of components forward associated the they and regions case, motion and by sign the that by Whether velocities is measured, abundant Ca+ violet galactic to Doppler the to complexes. Might HI in (Pimentel the for GUIDO interstellar future has and an • about parent Schmidt probable only on +66°1675 that settle originate of the but and the the Provided then, lines producing association Ca+ these than between material ionization-pressure CN density of the the lines been of with subsequent boundary: line emission of a stars CN it only of CH+ with longitudes observed observations. the this by 100 shifts case +7.5 of lines galactic hypothesis radicals (and MUNCH molecule not that arising constituents two or those the 2 the given respect long 1963), 1960) lines Unlike 3 errors amounts the S-3 effect in under one molecules is by distribution question pc and corresponds be the surrounding the with molecules. molecular are basis the the He km/sec, of a a nebula. of the realized. 3 molecular the observed from arise P star in result volume through M8-M20 raises rotation formed dissociation the possibly CH the in somewhat we I the the to involved is CH) is motion discussion observed two zn NASA Table of absorption case, that the between due the sublimated (6 molecular in find and case close in It firmly. the laboratory CN by of Observations 1 of radicals this with 0ri lines front the lines stars the surrounding can The Now, the near in then, along to the to Astrophysics high two-body shift the 1 CN in the of in that also galactic and molecules complex, agreement provide D) interesting in solid in range interstellar the immediate the CH+, be larger a stars the observed hypothesis results whole One 2 results of advancing embedded grains to lines nebula on +66°1675. the value in turbulence of and that shows are the He the noticed, are lines galactic a lower the opposite the inert this experiments, the CH, stable however, final 116°-119° of measurements I 8 known in mean plane, line in some not radiative Orion the from chances of the close absorption emission H km/sec A should do observed basis Shl has direction, a these absolute Data of in in matrices quality question. argument the neighborhood r CN CN nearly = of coexistent further, not parent of He rotation into in gas 71. unreddened specific the their It shift sense an some spiral in to it 15 sight. of 21-cm also Bates we molecules the System is two I is result be (Wilson, appreci­ of the 0.9 (Mi.inch (Mlinch appears our Vol. the Consid­ associa­ stars absorp­ km/sec formed region. known cannot undis­ of in of as radial Orion value form­ mole­ is to ante­ when then, stars CH4, arm, lines kpc. that H Evi­ The pre- of cool evi­ and line can 140 the the has the yet are be or as of n a 1964ApJ...140..107M ing been tion the No. --. trapped --. Jenkins, --. Herbig, Donn, Bates, Blanco, Adams, Sharpless, Osterbrock, Munch, Morgan, Merrill, Kraft, Sharpless, Pimentel, Munch, Dunham, Wilson, Academic © I York: and measuring 1, am of American emphasized B. R. D. 1964 interstellar V. 0. W. G. 1949, 1946, 1964, P. G., G. F. W.W., criticizing indebted Adademic in 1960, T., P., G. R., S., S. M., C., W. 1958, A., 1957, S. and D. Press), solid C. 1959, and Jr. and and Pub. ibid., unpublished. 1943, Munch, 1942, and and E. Formation 1960, Wilson, Astronomical Pub. Stromgren, 1941, and Ap. Schmidt, Spitzer, Osterbrock, 1957, Ap. cosmic A.S.P., Wooldridge, Williams, 109, chap. Press), Ap. to Ap. by radicals this J., Formation A.S.P., reduction Pub. G., J., Professor Ap. 354. J., 0. J., Donn 125, and 11. L., paper. Suppl., Flather, 58, M. chap. particles. C. 97, A.A.S., 95, J., B., A. Jr. 42. 70, D. Trapping 1962, 354. 1963, and 217. 125, 268. and D. Society and D. (1960), 1951, E. 4. 468. of My 4, Wilse INTERSTELLAR E. E., to 1959, 10, Zs.f. Johnson, 1952, Trapping 622. Ap. 257. the 1937, and Ap. Drs. thanks 123. of J., • Ap. observational Ap., Ap. who Free REFERENCES G. J., Coffeen, Provided Phys. 137, George H. J., Robinson of J., 113, 56, Radicals, are has Free M. 249. 130, 115, Rev., 127. 441. M. due 1955, also Radicals, H. Herbig 482. by 89. 1959, 33, CLOUD ed. also the for material. Ap. suggested 137. A. Ap. NASA his to J., ed. M. Miss J. and opinion 121, A. Bass Suppl., M. Astrophysics 611. John that Joyce and Bass concerning H.P. 4, E. free and 199. Sheeley Gaustad Broida H.P. radicals Data for Broida the (New System for some can forma­ York: read­ (New 111 be of