1943ApJ 97 . . 135A 3 4567 89 23 trum ofthestarissufficientlyintensetoblotoutanyforbiddenfinesthatmayappear. the average,asplanetarynebulaeandnormalstars. plausible assumptionsanattemptismadetofindthechemicalcompositionofatmosphericlayers.In tures oftheiratmosphericenvelopesareestimated.Thesetemperaturesturnouttobeveryhighandde- electrons/cm, muchgreaterthantheelectrondensitiesinenvelopeofanova.Thebackgroundspec- respect toothergasesisveryuncertain.ThenucleiofBD+30°3639andNGC40seembetypical from theabsorptionofhigh-frequencyradiationemerginglowerlayers.Onbasiscertain novae thantotheenvelopesofordinarynovae,whichappearhaveroughlysamecomposition,on carbon stars.ThenucleusofNGC6543,whichcontainsbothnitrogenandcarbon,seemstoshowarela- tential, thehigherresultanttemperature.TheemissionlinesinWolf-Rayetstarsprobablydonot pend upontheionizationpotentialofionemployed—insensethathigherpo- nitrogen andthreehundredtimesasabundantcarbon.Theestimateoftheabundanceheliumwith graph givesthedetailedresultsforspectralfinesandterms oftheatomsfirstrowperiodic superposed, characterizetheirspectra.Inrecentyearsidentificationsofthelinesand arise fromtheprimarymechanism,i.e.,photoionizationandsubsequentrecaptureofelectrons,butrather Payne, Edlén,andSwingsStruve.Bealshassummarizedthespectralfeatures wide andoftententimesasintensethecontinuousspectrumuponwhichtheyare derstood ofstellarspectra.Broademissionlinesatomicorigin,sometimes50or100A abundant ascarbon,whileinthenitrogenstarsheliumappearstobeabouttwentytimes and characteristicsoftheWolf-Rayetstars.Wehaveareasonablygoodideadi- tively smallrangeofionization. the carbonstarsheliumisestimatedtobeaboutfiftytimesasabundantoxygenandfifteen ity-curve byOlinWilsonandthelight-curveS.Gaposchkin. mensions andmassofoneWolf-Rayetstar,BD+38°4010,fromthespectroscopicveloc- the interpretationofWolf-RayetspectrahavebeendiscussedbyBeals,Menzel,Miss table intheirvariousstagesofionization. 92, 295,1940;93,349,1941;356,Proc.Nat.Acad. Sei.,26,454,1940;548,27,225, 1941; Pub.A.S.P.,52,394,1940;53,35,1941. 12 1 6 2 8 4 7 The electrondensitiesintheradiatinglayersofaWolf-RayetstarappeartobeorderlO^lO © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The chemicalcompositionoftheWolf-Rayetstarsseemstobemorecloselyrelatedthatsuper- The relativelyrareWolf-Rayetstarshaveperhapsthemostspectacularandleastun- From astudyofemission-lineintensitiesinnumberbrightWolf-Rayetstarsexcitationtempera- SocietyofFellows,HarvardUniversity. SeeP.Swings,Ap.95,112,1942.alsoSwingsandStruve, Ap./.,91,546,1940;92,289, Pop.Asir.,37,577,1929;M.N.,90,202,Pub.Dom.Ap.Obs.,4,272,1930. Although considerableattentionhasbeenpaidtothewavelengthsandidentifications *Pub.A.S.P., 41,344,1929. Ap.J.,91,379,1940;Mt.W.Contr.,No.623.* Ap.J.,93,202,1941. Zs.f.Ap.,7,1,1933. s B.Edlén,Zs.f.Ap.,7,378,1933;Nov.Ac.Reg.Soc.Sei.,Upsala,Ser.IV,9,No.6,1933.Thismono- /. R.Astr.Soc.Canada,34,169,1940. A STUDYOFEMISSION-LINEINTENSITIESINSOMEBRIGHT NORTHERN WOLF-RAYETSTARS Harvard CollegeObservatory 1 Received November28,1942 Lawrence H.Aller ABSTRACT 135 1943ApJ 97 . . 135A 1011 12 graphic region.Inaddition,acompletesetofphotometric standardswasimpressedupon grams finallyreduced;successivecolumnsgivethe object,theplatenumbers,dateof Lick Observatory.Thephotometricprocedureresembledthatofapreviousinvestiga- partly tosupplydataonrelativeradiatedenergies.Slitlessspectrogramscoveringthe lent widthofanemissionlineshouldbesupplementedbymeasuresthedistribution Payne andBealshavemeasuredtheprofilesofanumberemissionlines.Suchmeas- classification, andspectraltypesaccordingtoBeals. Fiveofthestarsbelongtoni- veloped togetherinDllunderconstantagitation. observation, andthespectralregioncovered.Generally, exposuretimesrangingfrom visual plates,blueandultravioletstandardsonthe platestakenespeciallyforthephoto- exposed inthetelescopereceivedtwosetsofstandards :redandgreenstandardsonthe blue, andultravioletwave-lengthregions,providedcalibrationstandards.Eachplate tion oftheplanetarynebulaeexceptthatspectrawerewidenedbytrailing.The ous backgroundareadequateformosttheoreticaldiscussions,buttheprofileorequiva- ures areoffundamentalimportancetoanyrealunderstandingtheWolf-Rayetspec- of theemissionlines,relativelylittleworkhasbeendoneontheirintensities.Miss radiated energies. convert intensitymeasuresofbrightlinesintoreasonablygoodestimatesrelative of thecontinuousenergy.Evenanapproximateknowledgelatterenablesusto trogen sequence,andthreetothecarbonsequence. Table2liststheforty-threespectro- an otherwiseunexposedplatetakenfromthesame box.Theentiresetofplateswasde- Mills spotsensitometer,usedinconnectionwithappropriatefiltersforthered,green, wave-length rangefromX3200to6400weretakenwiththeCrossleyreflectorof 37 3821. 35 4001. 35°3953. background. 43 3571. 38 4010. 36 3987. 35 4013. the intensityinemissionlineonlywithrespecttoofcontinuous tra, buttheymayprofitablybemadeonlyonrelativelyunblendedlines,andgive 36 3956. 136 LAWRENCEH.ALLER 12 10 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Ap./.,93,236,1941. StarsofHighLuminosity,p. 83,1930. Table 1liststheWolf-Rayetstarsobserved,their positions,magnitudes,Harvard I undertookaspectrophotometricstudyoffewthebrightestWolf-Rayetstars Measures ofanabsorption-lineprofileinordinarystarwithrespecttothecontinu- bd 91, 966,1931;Pub.Dom.Ap. Obs.,6,95,1934. 193077 193793 193576 192163 192103 192641 191765 190918 HD Wolf-Rayet StarsObserved THE OBSERVATIONALDATA h 20 17.1 20 15.8 20 13.3 20 10.8 20 20 20 20 2^2 8.4 8.1 6.5 TABLE 1 Position +35° 31' +43 38 03 38 37 07 35 54 35 53 36 21 32 25 Mag. 8.04 7.80 6.83 7.97 7:94 7.01 7.44 7.94 Harvard Type Ob Ob Op Oc Oa Ob Oa Oa Victoria Type WN6 WN5 WN6 WN6 WN5 WC6 WC7 WC7 1943ApJ 97 . . 135A BD+35°3953 BD+35°4001 BD+35°4013 BD+37°3821 BD+36°3987 BD+36°3956 BD+38°4010 BD+43°3571 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Object WOLF-RAYET STARS List ofObservations Plate 211 213/ 212\ 186 185 184 183 188 187 199J 191 1901 1891 267 265J 264 260J 259 2581 268 2661 2631 TABLE 2 Aug. 24,1939 Aug. 25,1939 Sept. 5,1939 Aug. 25,1939 Sept. 5,1939 Sept. 5,1939 Oct. 18,1939 Oct. 21,1939 Oct. 18,1939 Oct. 19,1939 Oct. 19,1939 Oct. 21,1939 Oct. 19,1939 Date ¡ultraviolet, blue /visual /blue ' /visual jblue fblue, ultraviolet fblue [visual [blue [ultraviolet [visual, blue [ultraviolet [ultraviolet [visual, blue [blue f visual ^blue Visual Visual Spectral Region ultraviolet ultraviolet blue ultraviolet ultraviolet blue visual visual ultraviolet visual ultraviolet ultraviolet ultraviolet visual visual blue visual blue visual, blue visual, blue ultraviolet ultraviolet visual blue 137 1943ApJ 97 . . 135A 138 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem b «-M Q PQ + CO d M p B O 13 LAWRENCE H.ALLER that ofablack-bodycurvefittedtothevisualregion spec- crease towardtheultraviolet;i.e.,theirenergycurvesrise above suggest thatthecolortemperaturesofanumberstars in- trum. Furtherinformationon thisquestionisverydesirable. photometric temperaturesofseveralearly-typestars. Color- given separatelyforthenitrogenandcarbonstars. be madethesubjectofacarefulinvestigation.Thepresent data a studyoftheenergydistributioninWolf-Rayetstars should as fromtheusualdifficultiesofphotometryinultra-violet, but temperature determinationssufferfromgalacticabsorption aswell movië (Harv.Circ.,No.339,1929),whomeasuredthespectro- ground continua.Thecontinuousspectrashouldbe at X4000ofunitequivalentwidthwillhavean inten- The unitofintensityissochosenthatanemissionline investigated withcareinstarssuitableforthispurpose. observed arenotsuitableforadiscussionoftheirback- plate sensitivity,highcontrast,lowdispersion,andfre- accuracy obtainableintheultraviolet. hand, atmospherictransmissiondifficultieslimitthe length error.Inthevisualregion,rapidlyfluctuating ground, estimatingtherelativecontributionsofoverlap- the precisionofmeasuredintensities.Onother quently strongemissionlinesconspiretomaketheloca- error, theintensitiesarelikelytosufferfromawave- faintly ortoostrongly.Inadditiontosuchascale tion ofthecontinuousspectrumdifficultandtodecrease affect aweaklinemorethanstrongone,inthesense ping bands,andsoon.Errorsindrawingthecontinuous ous spectrumtoohighinanemission-linestar—will spectrum—and oneusuallytendstodrawthecontinu- produced inFigure1,willillustratesomeofthedifficul- problem. Atracingofatypicalstar,BD+37°3821,re- that theweakerlineismeasuredsystematicallytoo pending uponwavelength. ties encounteredindrawingthecontinuousback- who plannedatthefirsttocollaboratewithmeonthis at theHarvardObservatorybyDr.F.L.Whipple, fog introducednoerror.Becauseofvignetting,especi- matic type,slighterrorsincenteringtheobjector ally troublesomeinaslitlessspectrographofthepris- on moonlitnights,theexposuresweresoshortthatsky strong lines.Althoughmanyoftheplatesweretaken ultraviolet. Anumberofplateseachstarhadtobe from thestrongestemissionlinestoweakin the comparisonstarmaygivesystematicerrorsde- taken, inordertorecordboththecontinuumand two tofifteenminutessufficedcoverthespectrum 13 TheonlydataonthisproblemseemtobethoseofGerasi- The tabulatedintensities(seeTables4and5)are With theexceptionofBD+35°3953,starsIhave The platesweretracedwiththemicrodensitometer WOLF-RAYET STARS 139 sity of 1.0. I estimate the accidental errors in the tabulated intensities to be generally of the order of 10 per cent for the stronger lines*14
IDENTIFICATIONS For the identifications of lines in Wolf-Rayet spectra I have relied chiefly upon the data of Edlén. I have also used Whipple and Mrs. Payne-GaposchknFs study15 of the synthetic spectra of Supernovae. This paper includes a complete list of multiplets in the astronomically accessible spectra regions with their semitheoretical intensities computed for specified temperatures from modem atomic theory by means of the summation mies and Einstein probability coefficients, supplemented by laboratory intensities. They have proved to be invaluable for the present study. Most of the Wolf-Rayet identifications by Miss Payne are verified. As would be expected, however, the intensity estimates of Whipple and Mrs. Payne-Gaposchkin enable us better to estimate the relative contribu- tions of various members of a blend. In Table 3 are collected the most important lines of multiplets of the ions of He i, He ii, O hi, O iv, 0 v, O vi, C n, C m, C iv, and N m, N iv,N v, and N vi observed in TABLE 3 The Principal Lines and Multiplets of the Ions Observed in the Spectra of the Wolf-Rayet Stars
Ionization Principal Lines Ionization Principal Lines Ion Ion Potential or Multiplets Potential or Multiplets Hei... 24.46 5876,4471,4026,3889 N iv. 77.04 3480,4058 Hen.. 54.14 4686, 3203, 5412, 4859, 4542 N v. 97.43 4609 Cn... 24.26 4267, 5140 O m. 54.62 3962,3760, 3708, 3265 Cm.. 47.64 4650, 5696, 4069 O iv. 77.03 3730, 3411 Civ... 64.17 5805, 3934 Ov.. 113 5590,5114 Am.. 47.20 4638, 4525, 4100, 3360 O vi. 137.48 3812, 3835
Wolf-Rayet spectra. Successive columns give the ion, the ionization potential, and the most outstanding lines. Although the radiations of C h and O m are divided among a number of strong lines, practically the whole observable energy of A” v or O vi is con- centrated in one line. The ionization potentials range from 24 volts to 137 volts. The successive columns of Tables 4 and 5 give the wave lengths estimated from the slitless plates of BD+37°3821 and BD+35°4013 for the nitrogen and carbon stars, re- spectively, the atom responsible; the laboratory wave length; the inner quantum num- ber, /, for the two levels of the transition; the multiplet; the strength of the line in terms of the strength of the multiplet as unity (in some cases), as computed on the basis of LS coupling; the theoretical intensity of the multiplet according to Whipple and Mrs. Payne-Gaposchkin; and finally the observed intensities and line widths for the various stars. In the column headed íTdentifications,,, I have listed for each Wolf-Rayet line the various contributors according to the atom and multiplet rather than wave length. The line widths, AX, were measured directly with the measuring engine; they are intended only as guides in the identifications. Although these AVs may have some significance in 14 It is extremely difficult to estimate the actual error in these intensities. The accidental error of a reasonably strong line measured on three or four plates is about 10 per cent, but this does not include systematic errors which may arise from estimating the continuous spectrum, for example. Weak lines, or lines in the far ultraviolet, may easily be in error by a full 100 per cent. Proc. Amer. Phil. Soc., 84, 1, 1941.
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1943ApJ 97 . . 135A 3203. 3360. 4471. 4380. 4512. 4100. 3483. 4540. 4340. 4025. 3965. 3930. 4057. 3705. 3889. 3733. 1200. 3750. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Nm Hen N iv Niv N m He i He i Hen N m Hen He I Nm He n N m N m Hen N m N iv Het Hen He i Hen He i Hen N m Hen He i Ion Emission LinesObservedinStarsoftheNitrogenSequence X (Lab.) 3203.16 4387.93 4338.71 4097.31 4100.08 4057.80 4025.64 3358.72 3353.78 4348.36 4323.93 4199.87 4200.02 3484.90 3374.06 4471.48 4541.63 4527.86 4518.18 4510.92 4471.69 4195.70 4103.37 4026.36 4026.19 3705.00 3478.69 3365.79 3361.90 4339.52 4215.69 3732.99 3705.14 3354.29 4546.36 4535.11 4547.34 4530.84 4523.60 4514.89 4335.53 4328.15 3968.47 3923.51 3888.65 3771.08 3747.66 3732.85 3367.36 4379.09 3964.73 3942.78 3887.47 3754.62 3482.98 4534.57 3938.52 3934.41 3745.83 2 2, 1 2,1 5/2 3/2 3/2 3/2 3/2 5/2 5/2 3/2 3/2 5/2 7/2 5/2 5/2 2,1 1/2 3/2 3/2 3/2 3/2 5/2 5/2 3/2 3/2 3/2 2,1 3/2 3/2 1/2 3/2 1/2 1/2 1/2 1/2 1/2 V 1/2 0 0 0 1 1 1 2 2 3,2,1 3,2,1 3,2,1 3/2 3/2 3/2 5/2 5/2 3/2 5/2 3/2 3/2 3/2 3/2 5/2 3/2 5/2 3/2 7/2 3/2 3/2 3/2 3/2 3/2 3/2 1/2 3/2 7/2 5/2 5/2 5/2 5/2 i/ 1/2 1/2 1/2 !/ 0 2 1 1 1 1 1 4 2 4 2 4 3p' D—3d'4D 3p' P—3d'D 3s' 4P-3p'4P 3p'S —3d'Po 3s' 4P-3p'4D 1X 8 8 2 8 2 2 2 3s'P-3p' D Ss'iP-Sp'iD 2 Sp^o-ScPD 3s4po-3pS 2 2 2 2 2 83 , 28po_43D 23po_73D 2P°—5D 23po—7S 2P° —5D 4fF—5gG 3sS—3pP 4F° —11G 4F°—12G 4F°—15G 3sS—3pP° Multiplet 3F—5F° 4F-10G 42F-9G 4F —13G 4F-14G etc. 42F-162D etc. 2S —3P° 2'S—4P° TABLE 4 0.14 s/2s 03 043 35 40 08 55 08 33 01 09 017 21 14 11 15 15 11 loot 58 It 33t 52 32 21 37f 84 16 10 18 10 1 +37°3821 86 62 43.4 46 14.4 21.8 25.7 73 15.2 11.5 5.8 9.0 9.0 3.0 7.2 6.7 7.2 BD AX 25 25 19 96 92 21.8 28.5 50.9 29.8 13.0 11.4 14.1 +35°4001 5.7 9.6 5.2 5.36 6.7 BD AX 20 42 +36°3987 20.3 12.9 11.7 11 4.1 5.4 4.2 5.8 BD AX 10 13 11.8 12 +38°4010 8.5 8.4 8.7 7.0? 6.3 7 BD AX 1943ApJ 97 . . 135A 16 17 7 grams arerequired.Therefore,Ishallnotdiscussthequestionoflineprofilesinthispa- per. ly smallerthanthosetabulatedbyBeals.Probablywesetonthebandedgesindifferent termination neitherofprofilesnorlinewidths.Forsuchaninvestigationslitspectro- ways. 4609. spectrum ofthesamestarapparentlyrequiresthat theobservedradiationsoriginateina ful studyofthespectraltermsnitrogenandcarbon.Fromaconsiderationtheoreti- tra suggestgreaterdeviationsfromconditionsofthermal equilibrium.Thesimultaneous noticed anyotherlinesofcarbonoroxygeninthespectranitrogenstarsIhave The lineatX5805inthenitrogenstarshasbeenattributedbySwingstoCivfromacare- 4633. may concludethat,whilethenitrogenstarson listcontaincarbon,thecarbonstars they arewidenedbyseeing,andhencepartlydistorted.MyAX’sconsistent- 5808. 5412. 4932. 4861. 4686. stratification. number ofdifferentlayers. Theatmospheresofthesestarsseemtoexhibit considerable contain nonitrogen. fines ofCivandmprobablywouldbemostlymaskedbytheX4640lineNm,al- cal lineintensitiestheauthorindependentlyreachedsameconclusion.Ihavenot the ultravioletforstarswithbroaderbands,itisclearthatinvisualregion 5876. appearance oflinesgreatlydifferingexcitation suchasthoseofEeiandA^vinthe even whenothernitrogenlinesarenotobserved, is notfoundinthecarbonstars.We though SwingssuggeststhattheX4638lineinHD192163seemstoextendtoofar studied, althoughX5695ofCmoughttobeobservable.The4658and4650 the redtobeattributedA"monly.Onother hand,X3483ofNiv,conspicuous 1617 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Op. cit. Pub. A.S.,10,157,1942. It isprobablyinaccuratetospeakofthetemperature ofaWolf-Rayetstar.Fewspec- Most ofthebroadlinesinspectraWolf-Rayetstarshavebeenidentified. Slitless spectraofthedispersionused,about100A/mmatHb,permitreliablede- N v Een Fei? N m Hen Een iV in Ee i C rv Ion THEORETICAL LINEINTENSITIESANDEXCITATIONTEMPERATURES OF X (Lab.) 4603.2 4921.93 4859.36 4640.64 4634.16 5812.14 4867.18 4861.33 4858.88 4858.74 4685.81 4641.90 4619.4 5875.96 5875.62 5801.51 5411.57 2,1 5/2 3/2 3/2 3/2 7/2 1/2 1/2 1/2 1/2 1/2 1/2 0 1 3,2, 1 5/2 3/2 3/2 3/2 3/2 9/2 5/2 3/2 7/2 1/2 1/2 1 7 2 3p' ^D-Sd4F THE WOLF-RAYETSTARS WOLF-RAYET STARS 3 2 2 3pP°—3dD. 2 20 2 2 2P0 —3D ipo_4iD 4F°-8G 3sS—3pP° 3sS—3pP° 3sS—3pP 32D —4F° 2 Multiplet 4F-7G TABLE 4—Continued 5/25 1240 100 100 lOOtj 100 4 4 270 +37°3821 40.8 38.3 15.5 11.7 5.6 BD AX 237 +35°4001 36.8 28.0 38.5 17.4 8.4 7.2 BD AX 58 50 36 +36°3987 54.3 11.8 9.8 7.4 ? BD AX 30 20 28 18 65 13.5 +3S°4010 9 8 6.7? BD 141 AX 1943ApJ 97 . . 135A 3965. 3930. 3889. 3835. 3815. 3758. 3708. 3607. 3560. 3445, 3429.. 3411. 3381, 3262. 3203. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem O m He i Si m Civ Cm He n He i O vi O vi He n He i O m O v He i O v O iv O m O m He i C in C m O iv O m O m He i O m O iv O iv O m O v O in He h Atom 3964.73 3961.59 3924.44 3936.41 3883.80 3885.99 3888.65 3889.18 3834.24 3833.83 3887.47 3811.35 3732.85 3736.78 3819.61 3819.75 3757.21 3754.67 3747.07 3744.73 3700.87 3759.87 3732.99 3717.11 3720.86 3703.37 3695.37 3698.70 3715.08 3702.75 3703.52 3707.24 3705.00 3609.61 3704.73 3608.96 3560.42 3705.14 3563.36 3712.48 3446.73 3554.44 3428.67 X (Lab.) 3554.57 3448.06 3444.10 3403.58 3450.94 3430.60 3411.76 3381.26 3384.95 3556.92 3455.12 3413.71 3385.55 3382.69 3275.67 3267.31 3260.98 3203.16 3382.85 3265.46 Emission LinesObservedinStarsoftheCarbonSequence 7/2,5/2 2, 1 1/2 1/2 2,1 5/2 2,1 5/2 2, 1 3/2 1,0 3/2 3/2 3/2 5/2 1/2 0 0 2 0 2 3 2 1 3 3 2 0 0 2 2 0 1 4 2 1 1 2 3 2 1 1 2 3 2 2 1 2 1 3 1 1 9/2,7/2 3,2, 1 5,2,1 3/2 1/2 2, 1 5/2 7/2 3/2 5/2 5/2 3/2 7/2 2 3 1 1 2 3 4 3 3 2 7/2 2 2 1 1 3 3 2 1 1 1 2 5 4 • 3 2 2 4 1 1 4 1 2 3 3 1 2 1 1 3 3 6 2 3 1 6 3 3 4 4 3p' D—3d'D 3p' D—3d'D 3p' D—3d'6F 3 3 3 3p' D-3d'F 3s' P—3p' 3 3 3 3p'P—3d' iP 2 2 2 3p' 6?-3d'D 2 4dD—5fF 3s' 5P-3p'5D 3 3s' P—3p'S 3s' P—3p'4D 3pD—3dF 2 3 2 3 1 3 2 3pD—3dF° 3siP-3piD 3pP—3dD 2 3 Multiplex 4pP—5dD 2sP—3pD 3pP—3dP 3pP—3dP 3pP—3dD 3sS—3pP 3sS —3pP 2P° —10D 4F-18G 2P—6D 4F-16G 2P —7S 2S-4iP 2S—3P 5S-62P 3D —5Fetc. 2P —7D TABLE 5 142 0.33 0.20 s/Zs .67 .47 .11 .25 .32 .14 .08 .42 .42 .21 .14 .14 .30 .43 Ü.óÓÓ lOOf loot 45 86t 33t 18 20 17 19t 33f 13t 7 4 9 17.1 17.9 +35°4013 22.7 13.6 40 15.3 16.4 41 11.9 12.1 7.7 2.9 3.0 8.2 9.0 7.7 BD 24 AX 11 +36°3956 22.2 4.4 7.6 BD 28 21 25 AX +43°3571 22 11 6.3 6.9 8.0 2.5 2.9 5.3 BD AX Notes 1943ApJ 97 . . 135A 4938. 4861. 4786. 4686. 4650. 4608. 4542. 4515. 4471. 4441. 4375. 4330. 4269. 4225. 4187. 4157, 4100. 4123. 4069. 4025. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem [He i jC m He i O iv He n C iv He n Civ C m C m He n Cm He i Civ Cm He n C in Cn 0 v 0 v 0 v C in Ov C m He i Hen 0 m Cm C m He i Ee n Atom 4921.93 4859.36 4798.25 4783.43 4785.6 4685.81 4664.5 4959.38 4656.5 4658.64 4665.90 4663.53 4646.5 4651.35 4650.16 4647.40 4593.47 4516.02 4541.63 4516.93 4471.69 4471.48 4441.81 4387.93 4388.24 4383.24 4379.97 4361.85 4368.14 4338.71 4267.02 4325.70 4267.27 4187.05 4178.72 4150.83 4156.50 4159.94 4121.70 4122.05 4152.43 4162.80 4135.86 4123.01 4100.08 4120.81 4081.10 4073.90 4070.43 X (Lab.) 4068.97 4056.06 4026.19 4123.90 4120.98 4026.36 4067.87 4025.64 3/2,5/2 5/2,7/2 7/2,9/2 5/2,9/2 5/2,7/2 3/2,5/2 1/2, 3/2 5/2 3/2 2, 1 3/2 5/2 2,1 2,1 2 2 0 1 1 1 1 3 2 1 1 1 3 2 2 3 0 1 2 0 4 1 1 1 2 1 1 3 2 2 0 1 3/2, 5/2 5/2, 7/2 9/2,11/2 1/2, 3/2 7/2, 9/2 5/2,7/2 3/2,5/2 5/2,7/2 3,2, 1 3,2, 3/2 1/2 0,1 5/2 1,2 2 0 0 2 2 2 1 1 1 1 4 5 3 2 3 3 1 2 3 3 3 3 1 ’ 5dD—6pP 3 3 3 3 2 3 3 3 2 3p' 4P-3d'4D 2 3 2 3p' D—5fF TABLE 5—Continued 2 1 2 2 3s' P—3p'P 3 4f' G—5g'H 4f' F—5g'G 4f'G—5g' H 2 3p' S—3d'P 3p' S—3d'P 1 3s' P—3p'D 3s' iP-Sp'iD 3s' P—3p'D 2 5dD —6fF 3 3 3s' P—3p'D 4dD—5pP 3s' P—3p'D 5gG —6fF 5gG —6hH 2 3 4pP—5sS 3dD—4fF 2 5pP —6dD 3 4dD—SPF Multiplet 5fF —6dD 5fF —6gG 4piP-5diD 3sS—3pP 3D-4F 2 4fF—5gG 21P-41D 42F-8G 4fF—5gG 2P°—5D 4F—9G 2P—4D 2P-51D 4F-10G 2P—5S 42F-122G 4F —13G 143 0.42 0.11 í/25 .11 .11 .33 .55 .47 .25 .11 .25 .08 .55. .11 .33 .47 100 100 100 It 12 19 17 14 4 1 2 238 11.2 73.6 20.8 10.0 +35°4013 17.0 27.4 11.4 10.3 3.8 7.0 5.2 5.2 3.5 7.6 5.1 9.0 6.4 9.4 8.2 4.9 BD AX 22 20 16 169 35.5 +36°3956 12.9 2.6 8 4.1 2.7 6.8 5.2 9.0 BD 20] 36 31 AX 26 176 43 11.7 +43°3571 13.6 11.6 14 6.6 5 7.5 BD AX Notes 1943ApJ 97 . . 135A 18 tive strengths0.35and0.15,havenotbeenmeasured. XX 4658.6,4656.5,and4646.5shouldbe990,504,210. enough forourpurposes.Thecalculationofeffective temperaturesrequiresaknowledge background overaconsiderablewave-lengthrange; wecannotdiscussthemhereforlack of the6-5transitionsandthatX4656.54646.5areweaker.According tothe/-filesumrules,relativestrengthsof 5019. of boththesizesandtotal brightnessesofthestarsinquestion,butthesequantities are of suitabledata.Gerasimoviö’smeasures,made some fifteenyearsago,arenotprecise 5302. 5132. this blend. 5876. 5805. 5412. 5257, does notcontributetothisline. 6235. 5592. 5470. 5695. X 4330and4375lines: 6147. 144 18 4 4 2 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Harv.Circ.,No.339,1929. 2. TheCn3d'D—4f'FmultipletatX4075forwhichWhippleandMrs.Gaposchkingiveanintensityof24probably 5. Theidentificationofthislineisunsatisfactory.strongerlines the CnquartetatX5145.16and5151.08,orrela- 4. Swingsconcludesfromtherelativelaboratoryintensitiesin.5-4 transitionsthatX4658.64mustbethestrongest Color temperaturesrequirecarefulspectrophotometric measuresofthecontinuous 3. TheCn3sP—3pP°multipletforwhichWhippleandMrs.Gaposchkinpredictanintensityof68maycontributetothe 1. TheCndoublet,3pP°—4sS,X3921,forwhichWhippleandMrs.Gaposchkinfindanintensityof74,maycontributeto O m O v Ov Ov Ov O iv He i Cn? C iv He i O m He n C m Atom C m Civ C m X (Lab.) 5017.7 5305 5268.06 5133.29* 5114.45 5015.68 5875.62 5603.9 5597.9 5580.0 5474.6 5418.3 5272.56 5244.5 5249.6 5015.9 6156.7 6155.4 5812.14 5801.51 5696.0 5411.57 5132.96 6154.4 5875.96 5592.37 5572.1 5253.55 5583.1 2 4319.65. 4345.57. 4317.16. 3/2 2, 1 3/2 1/2 1/2 V 1/2 0 0 0 2 2 1 1 5/2 3/2 3/2 1/2 1/2 1/2 2 1 1 1 1 1 LAWRENCE H.ALLER 3 TABLE 5—Continued 1 3 83 2 4 3p'iS-3diP 3s' P—3p'sS NOTES FORTABLE5 2 Ss'iS-Sp? Multiplet 4diD-5piP 38 2 3pP—3dD 3pP—3dP 5pP —6sS 3piP-3diD 1 3sP—3pP 3siP-3piD predicted 3sS—3p2P 2P—3D 4F—7G 2S—3P 0.14 0.14 s/2s .15 4366.91. 4349.44. 0.47 0.141 s/Zs .25 .15] .42 .08 .11 .14 100 lOOfJ 100 25f 4 2tJ 6 6t +35°4013 30.6 96 82.5 10.1 11.8 11.6 11.6 4.8 8.0 8.3 3.9 1.4 BD 0.15 0.35 s/'Ls AX 25 24 17 140 +36°3956 10.0 65 11.5 14 5.5 5.4 3.3 8.5 BD AX 24 53 200 +43°3571 33 62 12.3 10 17 18.5 BD AX Notes 1943ApJ 97 . . 135A populations ofcertainupperlevelstodefineanexcitationtemperatureaccordingthe an excitationtemperaturerepresenttheelectronofregionwherethese device. Thenearerthelevelsaretoionizationlimit,moreaccuratelyshouldsuch for whichS.Gaposchkinfindsaneffectiveabsolutetemperatureof13,000°.Ionization known foronlyoneWolf-Rayetstar,acomponentoftheeclipsingbinaryBD+38°4010, c andd,respectively(Fig.2).Let%axfobetheexcitationpotentialsofab, lines areproduced. excited levelswhichwetrytorepresentbyusingthisformulaassortofaninterpolation cannot estimatewellenoughforthesestars.Inthispaperweshalluseestimatesofthe ^4i and^4betheEinsteinprobabilitycoefficientsforlinesofwavelengthsXiX. Boltzmann formula.Themeasuredlineintensitiestellustherelativepopulationsof temperatures dependuponassumptionsconcerningtheelectrondensity,aquantitywe their wavelengthsbe\iandX,upperlevelsablower where A'oisthenumberingroundlevelofstatistical weightandwherethesumma- In thermodynamicequilibrium,hand/aregivenby tion iscarriedoutoverthelinesofamultiplet.The intensityratio/i//isrelatedtothe temperature Tby and Mrs.Payne-Gaposchkin.Then tiplets whoseuppertermsareaandb.Wemayuse theintensityestimatesbyWhipple 2 2 2 2 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Let themeasuredintensitiesoftwolines(ormultiplets)agivenionbe7iand/, Let /1andI°2bethepredictedintensitiesatatemperature Tofthetwoemissionmul- 2 0 7° =Cie-Xa/KT;p Ce-Xb/*T, 2 2 Fig. 2.—Schematicenergydiagram = 12 Sc0&^4v 2 I<2 ^'^2/£0¿.4, Zi =—' I) WOLF-RAYET STARS145 = -
Stars of the Carbon Sequence (a) BD+36°3956; (6) BD+35°4013; (c) BD+43°3571 1943ApJ 97 . . 135A © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem H-l w X HH H >magnitude. The last column of Table 9 lists the temperatures obtained by Beals by the application of the Zanstra method; they are generally higher than the excitation temperatures. In Figure 3, I have plotted the mean excitation temperature as a function of ioniza- tion potential. The points give the mean temperature for all stars for a given ion; ions of the same ionization potential have been grouped together. The individual points on which this curve is based show much scatter, but there is a marked indication that the temperature rises as the ionization potential increases. The interpretation is simple; a high temperature is required to multiply ionized atoms of carbon, nitrogen, and oxygen. As far as emission-line excitation is concerned, the temperature of the Wolf-Rayet star depends upon the type of atomic thermometer used.
THE CHEMICAL COMPOSITION OF THE WOLF-RAYET STARS Our plot of excitation temperature against ionization potential amounts to a plot of temperature against some function of depth in the star. The lower layers, wherein the radiations of ions such as C iv and O v originate, have temperatures of the order of eighty or a hundred thousand degrees, while the lines of O h and He i appear in the outer layers, where the temperature may be of the order of ten or twenty thousand degrees. This stratification of the Wolf-Rayet atmospheres makes a semiquantitative determination of their chemical composition difficult. We may know the temperature as a function of ion- ization potential, but we have no information concerning the increase of electron density with depth in the star. Nevertheless, I have attempted a preliminary analysis on the basis of my temperature calculation and line-intensity measurements. The amount of energy radiated per unit volume by Nn atoms in the level n in the line v is NnAhv, where A is the Einstein coefficient. The number of atoms in the level n is given by the combined Boltzmann and Saha equations28
UnN = 0bn T3/2 (27rw^)3/2a^5. e^i n/kT (12)
where bn is a measure of the deviation of the level from thermodynamic equilibrium, usn is the statistical weight of the level in question, and is the weight of the ground level of the ión> In=Xn — Xl, (13) where %i is the ionization potential of the atom, and %n is the excitation potential of the level in question. From (12) we obtain
2x )!!/2 E 16 N{Né = ( ^s _ ®>- T3fte-ijkT( = 2.39 X 10 £ h wnAhv wnAhv l (i4) = C\T3/2e~In/kTeE. .
^Ap. J., 92, 289, 1940. ™Ap. J., 85,336, 1937.
© American Astronomical Society • Provided by the NASA Astrophysics Data System 00LO
CT)O' 154 LAWRENCE H. ALLER
Because of its simple hydrogenic structure, we may write for He n 00 CT) NtN, hKg2RVZ Z ¿-'nn — Un ^3/2 n' n ’ e 2 hRZ an< = -32 where Xn — i ^ 2.097 X 10 . For any He n line our formula becomes
T Enn'=Cnn'bn^^-e^ , (15) 6 whence we obtain for X 4686 and two lines of the Pickering series, 5411 and 4542, the fol- lowing values of Cnn' and an:
4686. 3.92 X10-18 3.93X104 4542. 1.70X10"19 0.77 5411. 3.51X10-19 1.28
In the calculations I have neglected self-reversals and have assumed that the intensity of a line is simply proportional to E. I have adopted the temperature from the curve of
Fig. 3.—Relation between excitation temperature Fig. 4.—Relation between NiNe and ioni- and ionization potential zation potential
Figure 4 except for a few ions in some stars, where I have used the temperatures directly from Table 9. The gl4’s have been taken from Table 6. Table 10 lists the lines used in
the stars of the two sequences Cx and /n. Table 11 shows the values of log NiNe for the
various ions, expressed in terms of the value of NiNe for He n. Notice that, as the degree of ionization increases, so does the value of NdVe. I interpret this as meaning not that there is an overwhelming preponderance of the most highly ionized atoms of each sort, e.g., C iv, O vi, etc., in the radiating layers of the star’s atmosphere but rather that in the
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1943ApJ 97 . . 135A lower layersN*increasesrapidly,sothattheproductNiNrises.InFigure4,Ihave plotted logNiNagainst%forcarbonandoxygenBD+35°4013. mospheres ofthestarscarbon-oxygensequence.Thefactthatoxygenandcarbon Ov.. problem. Forexample,although OmandEeuhaveaboutthesameionization poten- O iv. Cm. Cn. O in. Civ. ionized, sothatrecombination linesofOmmaynotappear.Forthethree carbon-oxy- can existinseveralstagesofionization,whilehelium canexistinbuttwo,complicatesthe e tial, thelinesofHenmay yetberadiatedinthedeeperlayers,whereOiv hasaUbeen e © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Let ustrytocomparetherelativeamountsofhelium,oxygen,andcarboninat- Ion O in. Ov.. O iv. C ngivestherelativenumberofinionsmultipliedbyN. N iv. N m. Civ. Crv. Cm. ClI. e * ThistablegivesthevalueofN{NrelativetoiV,-iVforHen.Forexample, theentryfor €e 4441 4187 4267 4124 4069 3734 3562 3708 3934 3609 5590 3411 3760 5805 Ion Ion Factors forCalculatingAbundancesofVariousIons +37°3821 Values ofivwwithRespecttoHen t€ log Cx -2.91 -2.03 17.79 18.00 17.82 17.27 17.36 17.37 19.09 18.53 17.52 17.74 17.81 18 18 17.73 +35°4013 -0.5 —2.6 BD 0.95 2.38 2.20 19 17 1.47 1.30 BD WOLF-RAYET STARS +35°4001 24.66 39.2 25.24 29.70 14.21 15.91 13.95 18.32 4.86 4.86 3.36 6.05 5.98 5.00 •2.79 •2.20 BD 1.08 TABLE 11* TABLE 10 +43°3571 -0.5 —2.66 3.55 2.00 2.05 BD He ii Am N iv. +36°3987 -2.00 -1.27 BD Ion +36°3956 -0.30 — 2.14 2.00 0.97 1.20 BD +38°4010 -2.45 -1.10 BD 1.44 4200 4100 4686 4542 4638 4525 4380 3750 4057 3360 5411 3748 3483 Ionization Potential Ionization Potential 47.64 54.62 64.17 24.26 77.03 113.3 47.20 64.17 77.04 log Cx 18.77 17.77 17.58 18.45 17.41 17.88 17.27 18.05 18.23 18.26 18.11 18.69 18.65 27.05 24.13 16.92 14.25 15.43 0.90 4.57 9.06 8.50 8.12 5.89 7.61 1.49 I n 155 156 LAWRENCE H. ALLER
gen stars, the average N€N{He in) /NeN(0 iv) ratio turns out to be about 450. Evident- ly, this is a lower limit to the oxygen abundance. It would be the correct value if the He ii radiation were confined to the same layers as the 0 m radiation. The distribution of the oxygen atoms among the various stages of ionization within the radiating layers is unknown. Probably the number of oxygen atoms is not greater than ten times the num- ber of 0 iv ions, and it seems likely that most of the helium in these layers is doubly ion- ized. Therefore, we may conclude that within the limitations of our present knowledge a helium/oxygen ratio of about 50 is capable of explaining the observed features of the Wolf-Rayet stars. The problem of estimating the carbon/oxygen ratio is somewhat easier, as both may exist in several stages of ionization. We recall, however, that the C v ion is stripped to the K shell. Hence, in so far as the radiating layers are concerned, it acts like doubly ion- ized helium because the permitted levels lie several hundred volts above the ground level. Hence, to compare the abundance of carbon and oxygen, it is better to compare the NiNe curves for these atoms in the lower stages of ionization. In this way we find from the observed data for the three carbon-oxygen stars that carbon is about three times as abundant as oxygen in the carbon Wolf-Rayet stars. The carbon-oxygen ratio seems more constant from star to star than the helium-carbon ratio, although this may be an excitation or ionization effect.
Turning, now, to the stars of the nitrogen sequence, we find the N€N{Heni) /
NeN(N iv) ratio to be about 100. If about a fifth of the nitrogen exists as N iv, helium is about twenty times as abundant as nitrogen. We emphasize that these estimates are exceedingly rough, since we have no knowledge of the partition of the atoms among the various stages of ionization; it may well be that, in the nitrogen stars, nitrogen is more abundant with respect to helium than oxygen is in the carbon-oxygen stars. I have also estimated the abundances of carbon from C iv in the three nitrogen stars BD+37°3821, BD+35°4001, and BD+38°4010 by assuming that NiNe varies with depth in the radiat- ing layers in the same way as in the carbon-oxygen stars. The results suggest that carbon is about one-twentieth as abundant as nitrogen and roughly ten or twenty times less abundant than in the carbon-oxygen stars.
ELECTRON DENSITIES We may obtain an estimate of the electron density in the atmosphere of a Wolf-Rayet star from the brightness of the X 4686 line. Let us consider the Wolf-Rayet component of BD+38°4010, whose dimensions are known from the work of Gaposchkin and Wilson. The photographic magnitude of the binary is 8.39; and the magnitude of the X 4686 line, if it could be observed alone, would be about 11.0. We may apply to the Wolf-Rayet stars the theory which Menzel and I have developed29 for the calculation of the electron densities in planetary nebulae. For an order of magnitude estimate I shall suppose that the radius of the radiating layers of a Wolf-Rayet star is about 40 per cent larger than that of the star itself. The work of Swings suggests that this is about the correct order of magnitude. If the radius of the star is about twenty times that of the sun, the volume contributing to the Wolf-Rayet lines is roughly equivalent to that of a sphere of about 20 O, taking into account the occultation effects. If the emission per unit volume is 4^ E ', the total amount of energy radiated by a sphere of radius a is -r- E nfaz. The surface nn o n through which this energy must flow has an area 47ra3, so that the average surface bright- ness Sn will be ^Enn'a. Now, Menzel and I have shown that the surface brightness in terms of magnitudes per square minute of arc is given by
2 Sn = 8.40 X 10 (2.512) . (16) 93,195, 1941.
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1943ApJ 97 . . 135A -14 f 34 29 3011123 24 3 4 n123 123 radius of20Owillbe apply acorrectionfactor,Aw=2.5log(110X10)^—30,whence—19. Since thedistanceofstarisabout2600parsecs,angularradiusasphere From ourexpressionforEweget Accordingly, toreducesurfacebrightnessintermsofsquareminutesarc,wemust if theejectionvelocityofatomsis2000km/sec,totaldissipationmassbysuch i.e., 2X10gramscouldlastbut200,000years.Thisresultisindisagreementwith a processwouldamountto^lOgrams/yearandstartentimesasmassivethesun; sivity percubiccentimeteroftheHen4542lineand[Om]4363auroralline.For so thatwecansetNi=Nfind~10—electrons/cm.Thismeans If r^T36,000°andmostoftheheliumatomsareindoublyionizedcondition, al transitionstoyieldstrongerlinesthanthenebulartransitions.Sincedensityis sufficiently highforaBoltzmanndistributiontobemaintainedamongthemetastable that thetotalmassofWolf-Rayetatmosphereisorder6X10grams;and, levels, wehave temperatures anddensitiesprevailingintheWolf-Rayetstarswewouldexpectauror- the densitiesobtaininginWolf-Rayetstars.Letuscompare,forexample,emis- that ofBeals. where Nisthenumberofatomsin^levelandPlevel. n For theauroraltransitioninOm,IhavefoundthatA=1.97.Hence, line dependsverymarkedlyuponthetemperature. Thesecalculationsshow,however, ratio of4542to4363asgivenbytheaccompanyingtable.Theintensityauroral If thenumberofOmatomsis1/1000Heions,wefindintensity while 6je € sistent withadensityof10 -10 atoms/cmintheradiatinglayersoftheir atmospheres. thirty timeslarger.Iaminclined tofavorthelargervolume,about10thatofsun. that foradensityofKF-IOatoms/cm,theforbidden linesshouldbeatleasttwenty that thenonappearanceofforbiddenlinesinspectra oftheWolf-Rayetstarsiscon- times fainterthantheX4542Henline,i.e.,about 0.05onourscale.Wemayconclude 8v 30 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem It isofinteresttoinvestigatethepossibilityappearanceforbiddenlinesat Ifweadoptavolumeequivalent toasphereoftwicethesolarradius,densitycomes outabout 1267_3 E=9X10-N= 10“W,10“*/1.8X10(T=36,000°), 8îP 11 KF. 10. Ne 2017 ^.iV= 6.44X10(2.51)-^xP/0°—F—•(17) e 26 =7 £4542 =3X10-W, 0.0 93XT^VtrA610minutesofarc. € r =36,000°K _25 15 E= 3.7X10W¿e E= 2.14XlO-^(T=10,000°K), 170 17 095 “«t--' WOLF-RAYET STARS r =io,ooo°K 4 6 1.6X10 1.6X10 9 10 10. 10. 5040X 5.3 (r= 36,000°K), (r= io,ooo°k). Ne T r =36,000°K (lo.ooo) _1 0.17 1.7 r =10,000°K 2 3 1.6X10 1.6X10 157 1943ApJ 97 . . 135A 32 little confidenceindiameterscalculatedfromassumed temperatures. lines shouldshowavioletshiftandasymmetry.Sincesuchisnotobserved,we plains thegreatwidthsofemissionlines,absorptioncomponents,sometimesob- large-scale andviolentturbulence.ThemechanicsofaWolf-Rayetenvelopethe greater thanthevelocityofescape. large-scale turbulenceasapossiblecontributingcausetothewidthsoflines.The behind, sotospeak,asthestarmovesinitsorbit,thereshouldbeaphasedifferencebe- served ontheirvioletedges,andthefactthatradiationsofmosthighlyionized supposing thattheradiusof shellisaboutfourtimesthatofthestar,orbysomereabsorption phe- ing hypothesisandthatwemight explaintheabsenceofoccultationeffectinemission profilesby metastable levelswiththosearisingfromnormallevels.Thelattermethodassumesthat second shouldcomeintoplay.Sincesuchashiftisnotobserved,Wilsonconcludesthat served; andlargeoccultationeffectscausingavioletshiftofhundredskilometersper shows that,sincetheejectedlayerswhosevelocitywemeasurespectrographicallyareleft and emittingenergyontheredwardside.Onotherhand,ifshellislarge,Wilson should havetopostulateprocessesworkingabsorbenergyonthevioletsideofline atoms, whichoriginateinthedeepestlayers,arewidest,indicatingthatgasesac- If theradiatingshellissmall,apronouncedoccultationeffectshouldtakeplaceand celerated astheymoveoutward. stars tothecontinuousejectionofatomsfromtheiratmospheres.Thishypothesisex- from therelativeintensitiesofheliumlinesarisingnormal andmetastablelevelsverymuchabout radiation densitiesandare,therefore,subjecttolittleorno dilution.Consequently,onecannotconclude body. Untilenergy-distributionstudieshavebeen madeoftheseobjects,wecanplace culation oftheirdiametersfromabsolutebrightnesses itdoesnotseemlegitimateto with theconclusionsofGaposchkinandWilsonregardingdiameterWolf-Rayet work ofSwingssuggeststhatprobablytheradiishellsarenotmorethan50per The expansionhypothesishassomanyattractivefeaturesthatitdoesnotseemdesirable mospheres ofordinarystars,suggestdeep-seateddisturbancesintheWolf-Rayetstars. chief difficultyhereseemstobethattherequiredturbulentvelocitieswouldhave of Wolf-Rayetstars,theordertwicethatsun,areinmarkeddisagreement cent largerthanthoseofthestars.ThesizesthatheandBealshavederivedforanumber questionable assumptionthatturbulenceinWolf-Rayetatmospheresisnegligible.The component alongthelineofsight,withincylinderdefinedbylimbstar. the emissionlines.Theformermethodcomparesintensitiesoflinesarisingfromhigh transfer ofradiationthroughitprovideadifficulttheoreticalproblem. to discarditatthepresenttime.Onemightexpectanexpansionbeaccomplishedby the expanding-shellhypothesisneedsseriousmodification.Hementionspossibilityof Such aphasedifference,amountingtoasmuch1percentoftheperiod,isnotob- the geometricaldilutionfactor. Theysuggestthatwecontinuetousetheejectionmechanism asawork- component ofBD+38°4010.Thesestarsdonotradiate asblackbodies,andinthecal- The methodofthedilutionfactorseemsmorereliable,asitdoesnotdependupon Rayet starthelineexcitationsareproducedmostlyby emissionlinesoftheshell,whichattainlarge assume atemperatureandtoapplyformulavalid onlyforastarradiatingasblack the widthofvioletabsorptionlineismostlyduetorangeinejectionvelocity tween theeclipsespredictedfromspectrographicorbitandthoseactuallyobserved. Swings fromthedilutionfactorandbreadthsofabsorptioncomponents nomenon. 158 LAWRENCEH.ALLER 31 32 l © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Olin WilsonhascriticizedtheexpansionhypothesisinhisrecentpaperonBD+38°4010. The sizesoftheenvelopessurroundingWolf-Rayetstarshavebeenestimatedby Menzel andalsoBealsattributedthegreatbreadthsoflinesinWolf-Rayet Morerecently{Ap.96,262,1942)SwingsandStruve have suggestedthatintheshellofaWolf- *Ap. 95,1,1942. In anycase,physicalconditionsdifferingsowildlyfromthoseobtainingintheat- 1943ApJ 97 . . 135A 37 39 38 27 33 34 7 40 356 position ofthenebularimages.Theidentificationshavebeentakenfromtablefor graphic regionsofthesestarsarenowavailable.FortheidentificationsIhaverelied velope isnotadiskbutminutering.Theobjectsmallplanetarynebula.Wright ured anumberoflinesintheultraviolet,and,morerecently,SwingsandStruvehave studied thespectrumofcentralstarindetailfromX3342to6676anddescribedit often referredtoas“CampbelFshydrogen-envelopestar.”Wrightfoundthattheen- an arbitraryscaleandarenotadequateforadefinitivestudyofdilutioneffects.Slit in theneighborhoodofhydrogenlines,whereitwasnecessarytocorrectforsuper- The provisionalintensitiesofTable13,basedononlyoneplate,areuncertain,especially both strong,andthestarisclassifiedasWC8. carbon, andoxygeninvariousstagesofionizationcontributenearlyallthelines.Thein- wave lengths,identifications,andintensitiesofthelinesobservedinthisstar.Helium, made detailedmeasuresofthelinesinphotographicregion.Table12gives as “continuouswithmanysuperposedbrightlinesandafewdarkones.”Stoymeas- and, morerecently,Swingshavedescribeditsspectrumindetail. considerably narrowerthanintheordinaryWolf-Rayetspectra.ThenucleusofNGC mainly ontherecentpapersbyStruveandSwings. ample, andOlinWilsonhasannouncedthreeothersasspectroscopicbinaries. sorption lines,notablythoseonthevioletedgesofemissiondoubtlessoriginatein a continuousspectrum.Aremarkablefeatureof thisstaristhatitshowsthelinesof as thestrong3483lineofNivseemstobemissing. Thisstarappearstobeamoreorless tensities oftheweakerlinesaresubjecttoconsiderableuncertainty.Cnandm 6543 containslinesofcarbon,oxygen,andnitrogen,withcomparableintensity.Wright NGC 40,6543,andBD+30°3639.Provisionalintensitiesoflinesinthephoto- spectra shouldbeusedforthispurpose. stars areassociatedquitegenerallywithordinaryOorBstars.BD+38°4010isoneex- companions. MostOstarsarebinaries,anditseemsquitepossiblethatWolf-Rayet ing, andtheratherweaklinefoundinthisvicinity istobeattributedCiv,according C iv,NandOivwithcomparableintensity(see Table14),whileNmismissingand BD+30°3639. The3360bandmaybeduetoAm;butthisassignmentseemsunlikely, served thisstar,butthemostdetailedstudywasthatofWright.The4650bandisex- Rayet stars,foundthestartobesurroundedbyanenvelopeofhydrogen;itis,therefore, Fleming in1890.Later,W.Campbell,duringthecourseofhisstudiesWolf- stars. to Swings.Therangeofionizationislimited,as compared withtheotherWolf-Rayet the presenceofOmhasnotbeenconfirmed.The strong lineofCmnearX4650ismiss- tremely strongandstandsoutconspicuouslywhenviewedwiththeslitlessspectrograph. typical carbonstar. the atmospheresofWolf-Rayetstars;butothersmaycomefromnormalO-orB-type 4 36 35 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The interestingcharacterofthespectrumBD+30°3639wasfirstnoticedbyMrs. The nucleiofNGC40andBD+30°3639arecarbonstars,buttheemissionlines In 1938attheLickObservatoryIobservedspectraofthreeplanetarynebulae: *Pub. LickObs.,13,211,1913. The nucleusofNGC6543showsafew,relativelyfaint, emissionlinessuperposedupon The nucleusofNGC40displaysasomewhatsimilarspectrum.Paddockfirstob- Unfortunately, thepresentslitlessdatapermitonlyeyeestimatesofintensityon In someWolf-Rayetstarsabsorptionlinesarequiteconspicuous.Someoftheseab- Astr.andAp.,13,461,1894. A.N.,125,155,1890. ™Pub. A.S.P.,53,295,1941. THE SPECTRAOFNUCLEITHREEPLANETARYNEBULAE WOLF-RAYET STARS 33 39 37 40 Pub.A.S.P.,47,162,1935. Proc.Nat.Acad.Sei.,26,548, 1940. Op.cit.,p.221. Op.cit.,p.196. 159 1943ApJ 97 . . 135A 3760.. . 3774.. . . 3712-14. 3916-20. 3804.. . . 3791.. . . 3665.. . 3404.. . 3332-40. 3934.... 3889. 3813. 3703. 3640.0. 3609.4. 3564. 3445. 3294. 3285. 3264. 3202. 3165. 3132. 3820. 3503. 3412.9.. 3311. 3188. Wave Length * TheintensityofX4686ischosenas 1.00inTables12,13,and14. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Stellar Wave Length 13920.68/ f3918.981 \3166 j /3150 ' /3712.48\ \3889.18 /388S.65 /3816.75 /3813.53 \3608.96/ /3560.42\ /3609.61\ Laboratory \3563.36/ 13819.61 13715.08/ [3810.96 f3260.95 [3707.24J 13446.73 13444.10! '3702.75' '3440.39' 3934.1 3791.26 3774/00 3759.87 3403.58 3340.74 3330.40 3312.35 3299.39 3267.29 3265.41 3188 3132.87 3638.70 3450.941 3411.76 3333.00 3704.73 3703.37 O iv O in O hi 0 hi O in Si iv O III O in O iv He i Heij Om/ Hei\ O m\ O m O m O iv He ii O m Om O m Om He ii\ Civ C ii Cm/ C in Iden. The SpectrumofBD+30°3639 0.16 0.38 0.29 0.07 0.67 0.67 0.41 0.70 0.16 0.16 0.46 0.21 0.68 0.2? 0.32 0.1? 0.21 0.21 0.32 0.33 0.19 0.26 0.40 0.20 0.64 0.54 0.49 1.52 Int.* TABLE 12 .4414. 4186. 4163. 4155. 4120 4128 4115 4057. 4924. 4201. 4069. 4786. 4686. 4267. 4213. 4026. 4702. 4666. 3951. 4385. 4368. 4325. 4542. 4472. 4441. 4553, 4516. Wave Length Stellar Wave Length /4152.43 /4267.27 /4067.87 \4783.4 /4785.6 \4070.30 /4387.93 j4590.98 Laboratory [4156.50 [4267.02 [4388.24 [4596.19 Í4593.47 ^4647.40 4187.15 4162.80 4685.81 4212.44 4199.87 4128.05 4116.10 4056.06 4664.5 4663.53 4665.90 4658.64 4368.14 4120.81 4026 3951.82 4325.70 4656.5 4654.14 4651.35 4650.16 4541.63 4516.02 4471.48 4441.81 4414.89 4411.20 4411.52 4618.85 4552.61 4516.93 O iv/ He i He ii Si iv O m C rv/ Si rv O n O n Si m Hen He I On Hei\ Si iv Si ii He I He ii C m C m/ C m\ He I,n C iv Cm Cm C iv C rv C in C m Cn C m\ C ii Cm C m C ii/ C ii/ C m C m Cm C hi Cm/ C iv C ii Cm/ Cm/ C m\ Iden. 0.32 0.31 0.86 4.75 0.38 0.46 0.26 0.16 0.28 0.44 0.62 0.55 0.2? 0.43 0.53 0.77 0.2? 0.40 0.41 0.40 0.75 0.47 0.21 0.1? 1.00 1? 1.00 1.97 Int. 1943ApJ 97 . . 135A um ispresumablyabouttentimesasabundantcarbon.Wefindasimilarcomposition BD+30°3639 carbonappearstobeeightortentimesasabundantoxygen,whileheli- helium inthesestars.Itisdifficulttomakeaguessforhelium,buttherelativepropor- tions oftheotherconstituentsmaybeinferredfromdatawithlesstrouble.In for thenucleusofNGC40.Theobservationsmay be explainedbysupposingthatcarbon is sixtimesasabundantoxygenandthathelium isroughlytentimesasabundant have assumedtherelative abundancesofcarbon,nitrogen,andoxygentobe thesameas about equallyabundant, and carbonisfourtimesasabundanteither.The proportion the relativeproportionsof Civ,NandOiv.Oxygennitrogenthen appear tobe carbon. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem I havetriedtoestimatetherelativeabundancesofoxygen,carbon,nitrogen,and The compositionofthenucleusNGC6543is particularinterest.ForthisstarI 3203. 3345. 3266. 4028. 3445/ 3429\ 3411, 3381, 3360, 3963. 3925. 3560. 3889. 3609. Wave Length 3483 3411 3202 Relative LineIntensitiesintheNucleusofNGC6543 Line N in?? O iv Om He II O iv Om O TV Om He i Hei C ii,iv He i,Cin Cm Line IntensitiesintheNucleusofNGC40 Iden. N TV O iv He ii Ion WOLF-RAYET STARS 0.59 0.09 Int. 0.34 0.61 .21 .38 .74 .35 .30 .27 .27 .32 .28 .20 .18 Int. .92 TABLE 13 TABLE 14 4069. 4230. 4156. 4122. 4266. 4187. 4650. 4514. 4471. 4443. 4412. 4323. 4686. 4545. 4686. 4650, Wave Length Line He I,Cm He ii He i C III Hen Cm C m,Ov C iv C m C ii C m,rv C m Cn Hen C rv Ion Iden. 0.45 1.00 Int. 0.20 0.27 0.28 0.84 0.30 0.21 0.18 0.23 0.91 4.36 0.19 0.13 0.17 1.00 Int. 161 162 LAWRENCE H. ALLER of helium is more difficult to estimate. We may suppose that the helium radiations origi- nate at a much higher level than those of carbon, nitrogen, or oxygen. If this is true, we would expect the C m radiations to be present in the intermediate layers; but the evi- dence is strong that the C m is scarce, if present at all, and we are forced to the conclu- sion that in this star most of the radiations originate in a layer which is remarkably homogeneous in density and temperature. In that case the abundance of helium is prob- ably not much different from that of carbon, nitrogen, and oxygen ! The planetary nuclei present a number of interesting problems. Perhaps the most perplexing is that exhibited by NGC 40 and BD+30°3639, where nebulae showing strong nitrogen lines surround stars which show no trace of nitrogen in their spectra. While the ordinary Wolf-Rayet stars seem to fall into either the nitrogen sequence or the carbon- oxygen sequence, the planetary nuclei often show the lines of carbon and nitrogen with comparable strength. The planetary nuclei seem to be about 3 mag. fainter than the classical Wolf-Rayet stars, and their spectra sometimes display sharper lines.41 The ultraviolet temperatures of the nuclei of the planetaries may be derived from a comparison of the intensities of the Balmer lines and the forbidden lines by a method very similar to that suggested ten years ago by Stoy.42 The present method takes into account the finite electron temperature of the nebula, and the resultant temperatures of the cen- tral stars are a bit higher than those found by an application of the Stoy theory. The ul- traviolet temperatures of the nuclei of BD+30°3639, NGC 40, and NGC 6543 turn out to be 15,000°, 17,000°, and 47,000°, respectively. The significance of these temperatures is not too clear. Probably they are little more than rough indicators of the amount of energy radiated beyond the Lyman limit in these stars. The great range of ionization ex- hibited in certain planetary nebulae is difficult to reconcile with a central star radiating as a black body. The Wolf-Rayet stars, although few in number, appear to have considerable cosmo- gonic importance. Their lack of hydrogen sets them apart from all other stars, save the Supernovae. One suggestion which may prove fruitful is that these objects are supergiant stars that have reached the end of their energy resources. According to the Bethe mechanism, the stars of the main sequence shine by the conversion of hydrogen into helium. The rate of energy generation is so high for the B stars that we may expect them to bum up their hydrogen in a few million years. Since other nuclear sources are not known, we might expect the star to start contracting under its own gravitational attrac- tion. Under such conditions it is conceivable that the star might reach no equilibrium and might eject its atmosphere continuously into space. Chandrasekhar43 has pointed out that a star with a mass greater than Ms = 5.7Mo/fi (where Afo is the mass of the sun and /X is the molecular weight) must eject the excess mass before it can reach the final completely degenerate state. He has also suggested that the supernova phenomenon may result from the inability of a star of mass greater than Ms to settle down to the final white-dwarf stage without getting rid of its excess mass. It is tempting to suppose that the Wolf-Rayet process represents an alternative evolutionary path, whereby a massive star may eject its outer layers and ultimately attain a degenerate white-dwarf state.44 How close is-the relationship between the classical Wolf-Rayet stars and the planetary nuclei? Conceivably a Wolf-Rayet star on the downgrade might become a planetary
41 Dr. R. Minkowski has kindly informed me that several planetary nuclei, i.e., those of NGC 6751, IC 351, and NGC 6905, have bands of a width quite comparable to those of the classical Wolf-Rayet stars. NGC 1501 also belongs to this group, and there are indications that some of the fainter central stars are to be added when satisfactory spectrograms have been obtained. Dr. Minkowski further remarks that “if the ejection hypothesis is adopted to explain the great width of the nuclear Hues, the presence of a surrounding nebula with the usual small range of velocities appears not quite satisfactory.” This addi- tional difficulty in relating the nebulae and their central stars is not to be overlooked. 42 M.N., 93, 593, 1933. ™ Ap. /., 96, 172, 1942. 44 Goldberg and Aller, Atoms, Stars, and Nebulae, p. 277 (in press).
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1943ApJ 97 . . 135A 45 47 46 nebulae. Thevelocitiesofejectionwouldhavetodiminishconsiderably.Furthermore, nucleus, butitseemsdifficulttocreditthesestarswiththeoriginofplanetary processes ingaseousnebulaemaybeappliedtoananalysis of theenvelopesnovae.Ifwesupposethat, emission linesareconspicuous.Table15liststheintensitiesofabsorptionases- convenient toregardtheplanetarynucleiandclassicalWolf-Rayetstarsassome- no satisfactoryexplanationhasyetbeenpresented.Forthetimebeing,wemayfindit ments. Nevertheless,onanyhypothesis,thedisparityinchemicalcompositionbetween seem tobecomposedessentiallyofheliumbutwithvaryingadmixturesotherele- what differenttypesofobjects—insize,luminosity,andsometimeschemicalcomposi- mostly ofhydrogen.Ontheotherhand,wehaveseenthatWolf-Rayetatmospheres tions. Fromnovatothereareindicationsofappreciable variationsoftherelativeamountselements stars, itispossibletoexplaintheobservedemission-lineintensities withtheaidofafewplausibleassump- on theaverage,compositionofenvelopesnovaeis thesameasthatofenvelopesnormal ejection velocitiesarelow.ThemethodsdevelopedbyMenzelandhiscolleaguesforthestudyofphysical The X4543and4517linesarewellseparateddistinct;46404100fairly normal andmetastablelevelsindicatesthatdilutioneffectsofthetypedescribedby those ofionizedheliumareparticularlyintense.Absorptionlinesonthevioletedges the studiesofWyseandBowenothershaveshownthatplanetariesconsist the nucleiandnebulaesurroundingthempresentsafundamentaldifficultyforwhich been made.Forthepresent,however,itseemssafetoassume thattheenvelopesofnovaearemorenearly diffuse. TheonlylineobservedinthevisualregionisX5414. The simultaneousappearance,withcomparableintensity,ofHeilinesarisingfromboth tion. timated onanarbitraryscale;“s”and“d”signifysharpdiffuselines,respectively. pressure. Suchanadhocexplanation seemshighlyunlikely.Itisverydifficulttoassign reasonsforthe the atmosphereofnucleiobjectslikeBD+30°3639or NGC40weresuchastosuppressalltheni- akin tothoseofnormalstarsandtheplanetarynebulae thantotheWolf-Rayetstarsandsuper- are theeffectsofphysicalconditionscannotbesettleduntil adetailedinvestigationoftheproblemhas such asneonandsulphur,however.Towhatextentthese variationsarerealandtowhatextentthey supposedly wouldhavebeenejected, butheliumwouldhavebeenretainedbythestar.Menzel {Harvard novae. that theemissionlinestendtobebroaderandabsorptionarelessconspicuous. nonappearance ofanynitrogen linesinthesestarsifappreciablenitrogenispresenttheir atmospheres. trogen radiationsandthatthesurroundingenvelopeconsisted ofselectivelyejectedgases.Hydrogen Struve andWurmarenotimportant. Reprint 161)hassuggestedthe possibilityoftheseparationhydrogenandheliumbyselective radiation 45 46 47 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem BD+36°3987 hasmuchweakerandnarroweremissionlinesthantheothertwostars. Amoreattractivehypothesisisthattheplanetarynebulaeoriginatefrom“slownovae,”whose BD+35°4001 showsaspectrumverysimilartothatoftheprecedingobjectexcept 1. Thenitrogensequence.—BD+37°3821showsstrongemissionlines,20-30Awide; LickObs.Bull.,19,1,1939;seealsoAp./.,95,356,1942. Itmightbepossibletosavethesituationifwecouldshow thattheconditionsoflineexcitationin 4471 4605 4686 5056 5876 0 Absorption LinesintheSpectrumofBD-l-37382l Int. 3? 4 3 8 Is NOTES ONINDIVIDUALSTARS WOLF-RAYET STARS He i He n He I N v N iv Ion TABLE 15 3483. 4025. 3889. 3930. 10 Int. 8d 2 1 N iv He I Hei N m Ion 163 1943ApJ 97 . . 135A 1 9 gives theabsorption-lineintensitiesonanarbitrary scale,wavelengths,andassociated 4861 Ihavederivedroughwavelengthsforanumber oftheabsorptionlines.Table16 yond X3800theintensitiesarebaseduponasingleplateandtoberegardedasdis- ured onslitlessplates,arerelativelynarrow,andmostofthemhavebeenidentified.Be accord withthelowtemperaturefoundbyGaposchkin.Additionalobservationsofthis ber ofweakbandsupontiietracing.Themeasuresthecontinuousspectrumarein stars. Theintensitytables ofWhippleandMrs.Payne-Gaposchkingreatly aidedthe nothing unusualintheabsorptionspectrumtodifferentiate itfromotherabsorptionO many Wolf-Rayetstarsarecomponentsofbinaries. Bealsremarksthatthereappears spectrum iscomposite,showingabsorption07and emissionWC6characteristics.Such but highermembersareweak;X4471ofHeiisvery weak.LinesofOm,iv,andv beyond X3700.TheCmandivlinesXX5805,5696,4650arethedominatingfea- analysis ofthespectrum andthedisentanglementofoverlappingemission lines(see an associationofemissionandabsorptionspectra is consistentwiththesuggestionthat are inevidence.Fromtheassumedwavelengthsof theemissionlinesXX3708,4069,and emission linesforthisstar. terval fromX3700to6400becauseoftheoverlappingimageamuchbrighterstar tures ofthespectrum.TheHenXX4686,5412,4861, and4343linesareeasilyvisible, the starsofprogramandhasbeenusedasbasisTable5.Thelines,meas- star aredesirable. tinctly provisional. ous spectrum. Table 17). 164 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem BD+43°3571 exhibitsbroadbandswhicharedifficult tomeasureandidentify.The BD+36°3956 isacarbonstarforwhichthedataarerestrictedtowave-lengthin- BD+35°3953 showsweaklinesofXX4686,3483,and3203uponanotherwisecontinu- BD+38°4010 showsonlyX4686withhighintensity,althoughIhavemeasuredanum- 2. Thecarbon-oxygenstars.—BD+35°4013containsthegreatestnumberoflines 3871. 3800. 3780. 3748. 5590. 5696. 5805. 5876. Wave Length Approximate Wave Length The StrongestEmissionLinesinBD+43°3571 Int. 200 Associated Emission 21 62 33 0 3889 3760 Line Absorption LinesinBD+363956 LAWRENCE H.ALLER Contributor Principal O v He I C m C iv Int. 0s 2 5 1 TABLE 17 TABLE 16 4650. 4686. 3400. 4194. 4098. 4293. Wave Length Approximate Wave Length Int. Associated 176 Emission 43 22 4330 4121 Line Contributor O m,iv He ii C m Principal Int. 5 2s Id 1943ApJ 97 . . 135A low dispersionseemtobethemostsuitableforstudyofbroadlinesinsuchastar line, theexcitationofwhoseupperlevelis20voltslowerthanotherrelevantlevels lines canbemade. before acompletestudyoftheintensitiesandprofilesemissionabsorption spectrograms ofanumberWolf-Rayetstars.Additionalplateswillhavetobesecured ultraviolet, areurgentlyneeded.Also,additionalworkontheprofilesandintensitiesof probably theprincipalcontributortoblendat3820. strongest line,4650,inthephotographicregion,andalsostrong5696line.TheCiv5805 Payne-Gaposchkin forhelpfuldiscussionsoftheproblemsWolf-Rayetstars. been satisfactorallyidentified.InanumberofcasesIhaveattemptedtoestimatethe broad bandsofthespectrumBD+43°357l,mostobservedseemtohave principal contributortothebroaddiffusebandnear4266line.Cmcontributes have madenumerousvaluablesuggestions.IamgratefultoDirectorBobrovnikoffand Thanks arealsoduetoDr.O.C.Wilson,andR.Minkowski,P.W.Merrill, as BD+43°3571. relative contributionsofthedifferentmembersablend.Slitlessplatesrelatively ion leadstoanexcitationtemperatureof70,000°.The5590Ovbandisstrong;vi observed. Acomparisonofthe3386-3411bandOivwith3562same ence ofOiicannotbeestablished,the3762and3205lines,principallyduetom,are and 3202linesalsoby5414;theotherareweakblended.Cnmaybe is missing,andX3889maybeapartofblend.Z/enrepresentedbythestrong4686 of Harvard,whohavereadoneortheothersuccessiveversionsthispaperand of LickObservatory;Dr.O.StruveandP.Swings,Yerkes;D.H.Menzel, of theMountWilsonObservatory;Dr.C.S.Beals,Victoria;lateA.B.Wyse, Dr. J.A.HynekofthePerkinsObservatoryforopportunitysecuringsomeslit to securetheplatesusedinthisinvestigation.IamindebtedDr.WhippleandMrs. this ion,isparticularlystrong.Alltheotherlinesappearinblends.Althoughpres- the emissionlinesshouldbedone. © American Astronomical Society Accurate measuresofthecontinuousspectraWolf-Rayetstars,especiallyin He iexhibitsastrong5876line;X4472seemstobemixedwithbroadblend,4026 I amgratefultoDirectorWrightoftheLickObservatory,whomadeitpossibleforme Despite thedifficultyofdisentanglingoverlappinglinesthatcontributeto WOLF-RAYET STARS165 Provided bytheNASA Astrophysics DataSystem