19 93ApJS. . .85. .137M -51 1 among massiveearly-typestars(Barlow1982;Abbott&Conti tionally unbound.Thismassloss,oftencalledstellarwind,is these broademissionfinesareindicativeofathickexpanding widths aresohighthattheoutflowingstellarmaterialisgravita- few times10Myrandterminalwindvelocitiesof1000- Klein 1975).W-Rstars,typicallyhavingmasslossratesofa suggested tobedrivenbyradiationpressure(Castor,Abbott,& atmosphere. Theexpansionvelocitiesimpliedbythefine (Wolf &Rayet1867).Sincethenithasbeenunderstoodthat cally bytheirbroademissionfinesinavisualsurveyofthesky 3000 kms",arethemostpowerfulsourcesofstellarwinds winds orejecta,ofthecentral W-Rstars(Chu&Treffers1981; bles consistingofinterstellarmaterial(seeWeaveretal.1977 ). Esteban etal.1990). senty 1982;Smithetal.1984, 1988;Dufour1989;Chu1991). cumstellar materialthatthestellarwindsinteract(Solf&Car- that notallringnebulaecanbedescribedaswind-blownbub- Galactic W-Rstarsthathavebeensuggestedtobein ring González &Rosado1984).InTable1wecompileafist of winds sweepinguptheambientinterstellarmedium.Many Johnson &Hogg(1965)reportedthefirstthreering-shaped Still otherringsareionizedby theUVflux,butnotshapedby nebulae containmostlystellarmaterial,anditiswiththis cir- In somecases,e.g.,Ml-67,NGC6888,andRCW58,the ring nebulae. fied (e.g.,Johnson1975;Lortet,Niemela,&Tarsia1980; © 1993.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. Bruhweiler, &Gull1982),andafewwereindividuallyidenti- systematic searches(e.g.,Smith1967;Chu1981;Heckathom, more ringnebulaearoundW-Rstarswerefoundinsubsequent and suggestedthatthenebulaewereshellsformedbystellar nebulae aroundW-Rstars,NGC2359,6888,andS308, The AstrophysicalJournalSupplementSeries,85:137-143,1993March 1987). 0 Wolf-Rayet (W-R)starswerefirstidentifiedspectroscopi- Follow-up studiesofthesenebulaehaveshown,however, Nearly acenturyaftertheinitialidentificationofW-Rstars, A NEWSURVEYOFNEBULAEAROUNDGALACTICWOLF-RAYETSTARSINTHENORTHERNSKY Subject headings:ISM:general—:Wolf-Rayetsurveys around mostW-Rstarsisdiscussed. physical informationisderivedfromtheimprovedimagesofknownringnebulae.Theabsencenebulae ring nebulaearoundW-Rstarsnumber113,116and132,possiblenew number 133and153.AllsurveyimagesshowingnebulositiesaroundW-Rstarsarepresentedinthispaper.New representing acompletesurveyofnebulaearoundGalacticW-Rstarsinthenorthernsky.Wefindprobablenew Interference filterCCDimageshavebeenobtainedinHaand[Om]X5007for62Wolf-Rayet(W-R)stars, © American Astronomical Society • Provided by theNASA Astrophysics Data System 1. INTRODUCTION Department ofAstronomy,SanDiegoStateUniversity,Diego,CA92182; and DepartmentofAstronomy,UniversityIllinois,Urbana,IL61801 Department ofAstronomy,UniversityIllinois,Urbana,IL61801 Received 1992May4;acceptedAugust6 Grant J.Miller You-Hua Chu ABSTRACT AND 137 -1 f/7.5 secondaryanda3.0Xfocal reducer,whichyieldedf/2.5 Observatory (MLO).Theobservationsweremadewith the and September28,usingthe1mtelescopeatMountLaguna that donothaveanyringnebula.Asummaryisgivenin § 6. greatly improvedbyadedicatedsurveyusingsensitivemodem and the15pmpixelsizecorresponded to0?98.Thefull-width TI 800XCCDwasused. Thetotalfieldofviewwas13T, for thetotalsystemandan imagescaleof65'3mm.A ines fourknownW-Rrings.Section5discussesthestars describes theobservationsandpresentsresults.Section 3 and toexaminetheinterstellarenvironmentsofW-Rstars. nebulae, toobtainhigh-qualityimagesofknownW-Rrings, ( 1981).Ourobjectivesarethree-fold:tosearchfornewring around GalacticW-RstarscatalogedbyvanderHuchtetal. detectors andnarrowinterferencefilters. reports theprobableandpossiblenewW-Rrings,§4exam- This paperreportsthesurveyfornorthernsky.Section 2 photographic materialtakenwithbroadfiltersorlowspatial last decade,thesurveysofringnebulaeinearly1980sbe- eled todeterminethestellareffectivetemperatures(Rosa& resolution. Theycouldhavemissedmanynebulaewithlow came primitivebycontrast.Allprevioussurveysusedexisting Mathis 1990). (Esteban etal.1992).Thephotoionizednebulaecanbemod- interstellar material.Theelementalabundancesofejecta-type blown bubblesprovideagoodlaboratorytostudythedynami- surface brightnessorsmallangularsize.Thissituationcanbe nebulae canbeusedtoprobethestellarnucleosynthesisyield cal interactionbetweenstellarwindsandthecircumstellaror used tostudyavarietyofastrophysicalproblems.Thewind- The surveywasconductedonthenightsof1991June1-7 Therefore, wehavestartedanewCCDsurveyofnebulae As studiesofW-Rringnebulaegrewsophisticatedoverthe These differenttypesofnebulaearoundW-Rstarscanbe 2. OBSERVATIONSANDRESULTS 19 93ApJS. . .85. .137M Being limitedbytheamount ofobservingtime,wecouldnot of 5015Á,aFWHM49 andapeaktransmissionof55%. wavelength of6567Á,aFWHM of62Á,andapeaktransmis- sion of60%.Thisfilterwasbroad enoughtoincludeboth[Nn] the nebulaeifdetected.TheHa+[Nn]filterhadacentral WR 128(inFig.1[Plates5-11])showsmuchworsestellar XX6548, 6584lines.The[Om] filterhadacentralwavelength used inthesurveysothatwecoulddiagnoseexcitation of images appearinpoorfocus.Forexample,the[Om]image of can beasbad4"-5"atplaces. realistic spatialresolutionoftheseCCDimagesis~2", and images attheNEandSWcomersthanthosenearcenter. A the edgesofourfieldview.Examinedclosely,stellar The focalplanewasnotflatandcausedsomeastigmatism at at halfmaximum(FWHM)oftheseeingwastypically <2'' 138 Two filters,centeredattheHcxF[Nn]and[Om]lines,were © American Astronomical Society • Provided by theNASA Astrophysics Data System paper; (h)Cohen&Barlow1975;(i)Crampton1971. Lortet etal.1980;(d)&Testor1981;(e)Johnson1975;(f)GonzálezRosado1984;(g)this “possible.” “probable.” Hucht etal.1981). 157 153 140 152 139 136 134 133 132 131 130 128 127 124 093 091 085 075 052 048 024 023 116 113 102 055 040 018 WR 022 Oil 007 006 (1) Col. (8).—Referencesforfirstidentification:(a)Johnson&Hogg1965;(b)Smith1967;(c) Col. (7).—RingnebulaerecognizedbyChuetal.1983.“pr”for“probable,”and“po” Col. (6).—RingnebulaeidentifiedbyHeckathometal.1982.“D”for“definite,”and“P” Col. (5).—RingnebulaetabulatedintheSixthCatalogueofGalacticWolf-RayetStars(vander Col. (4)-—Nebulaname. Col. (3).—SpectraltypeoftheW-Rstar,takenfromvanderHuchtetal.1988. Col. (2).—NameoftheW-Rstar. Col. (1).—vanderHuchtetal.’s1981catalognumberoftheW-Rstar. HD 219460 HD 211853 HD 211564 HD 193793 HD 193576 HD 192163 HD 191765 HD 190918 HD 190002 MR 97 HD 187282 LS 16 HD 186943 HD 168206 HD 157504 HD 155603B LSS 4368 HD 147419 HD 117688 HD 115473 HD 113904 HD 92809 HD 96548 HD 93131 HD 92740 HD 89358 HD 68273 209 BAG ST 1 HD 56925 HD 50896 Name St Sa1 (2) WN4.5 WN6+0 WN5+06 WN3 WC7+04-5 WN6 WN6 WN4.5+09lb WN8 WC6 WN7 WN8 WN4 WN4+09.5V WC8+08-9IV WN8 WOl WC7+07-9 WN7 WN6 WN6 WN7 WC5 WN8 WC6+09.5I WN7 WC6 WN7 WN5 WC8+09I WN4 WN5 Type Spec. Wolf-Rayet StarsandRingNebulae MILLER &CHU _ÜÜ Anon (MR100) Anon (MR99) Anon (MR98) NGC 6888 Anon (MR95) Ml-67 Anon (ST1) S157-B S132 L69.8+1.74 NGC 6357 Anon (MR46) Anon (0Mus) S109 S109 G2.4+1.4 RCW 122 RCW 118 RCW 104 Anon (MR26) S132 S98 RCW 78 RCW 58 S92 NGC 3199 Gum NGC 2359 S54 Nebula Name Nebula S308 TABLE 1 ; column(3)liststhespectral typeofthestar,asgivenby in Table2:column(1)liststhe catalognumberoftheW-Rstar ( vanderHuchtetal.1981);column (2)listsothernameofthe traction andflat-fielding.Domeflatsineachfilterweretaken ranged from180to1200s.The observationsaresummarized were observedatleastonceinHa+[Nn];28also ob- the completelistdowntoadeclinationof-26°.All62 stars was asafeprocedurebecauseno[Om]-brightnebulaewere taken onlyifnebulosityinHa+[Nn]hadbeendetected. This served in[Oin].Thestandard exposuretimewas600s,but at theendofeverynightforflat-fieldingcalibration. known tocompletelylackHaemissionintheirvicinity. take [Om]imagesforeveryW-Rstar.were sis Facility)andfollowedthestandardprocedureofbias sub- (5) The datareductionusedIRAF(ImageReductionandAnaly- Sixty twoGalacticW-Rstarswereobserved,representing WR Catalog HBG (6) r CTK Others m (Q) pr pr pr pr pr pr po pr pr pr pr po pr pr po pr P pr 19 93ApJS. . .85. .137M Miller &Chu(see85,138) © American Astronomical Society •Provided bythe NASAAstrophysics Data System

fig. 1.—CCD images of galactic W-R stars in the northern sky. The number above the upper left corner of each picture is van der Hucht et al.’s catalog number of the W-R star. The filter is PLATE 5 labeled at the upper right corner: “H” for the Ha+[N n] filter and “O” for the [O m] filter. The field of view is ~ 13!1 X 13!1 for each picture, with north up and east to the left. 19 93ApJS. . .85. .137M PLATE 6 Miller &Chu(see 85,138) © American Astronomical Society •Provided bythe NASAAstrophysics Data System

fig. 1—Continued 19 93ApJS. . .85. .137M Miller &Chu(see85,138) © American Astronomical Society •Provided bythe NASAAstrophysics Data System v CVJ*.;. v’, cvj *;y*'■ h- h-„«*».* •'*.*vvvjk-•».;'ML•*♦*.••« 4 wÈêmmëâ I. P ■.• ÏËSËÈ ■ -...••-V• » f;*.*i' f *i - ^■WÊÊMf » 4,tz'**'’•. f yf 7;*.;i*V*'*;' 4 • yf*.*Î;"Í•‘•.¿i«-*** ♦il ^tïéÊbLf"*J}?s***l'% m |ÍI| -H..-U*;.■/ 0 • . * : I*. ♦Í f1% ‘ -i"■•,.•••;•>.%;.*'*».♦ . •<,-J•*-%-:»'m**;«.? u :||| *#*•<»,\J>'*''***$,% ., *.•.;J'*,mW*•**«*%* I:i # ^ *Jf*,•r'*»*#(f*♦♦«I*** ( 44X % ^ d**A*.♦ •\'f*-3 <•.**W**&S+**’»'«:J% 4 Ü ¿’iV^;;H5'' S/ ^*«,i,* -y--■7. 4*.*”?.7. % .ir. •

fig. 1—Continued PLATE 7 19 93ApJS. . .85. .137M PLATE 8 Miller &Chu(see85,138) © American Astronomical Society •Provided bythe NASAAstrophysics Data System

fig. 1—Continued 19 93ApJS. . .85. .137M Miller &Chu(see 85,138) © American Astronomical Society •Provided bythe NASAAstrophysics Data System

fig. 1—Continued PLATE 9 19 93ApJS. . .85. .137M PLATE 10 Miller &Chu(see85,138) © American Astronomical Society •Provided bythe NASAAstrophysics Data System

■Continued 19 93ApJS. . .85. .137M Miller &Chu(see85,138) © American Astronomical Society •Provided bythe NASAAstrophysics Data System

fig. 1—Continued PLATE 11 19 93ApJS. . .85. .137M ill- WR 147 145 144 143 113 111 108 007 006 005 004 002 158 156 155 149 146 142 141 139 116 114 112 110 107 106 105 104 102 003 157 154 153 152 151 150 148 140 138 122 120 119 118 117 115 001 137 136 135 134 133 132 131 130 129 128 127 126 125 124 123 121 Col. (2).—NameoftheW-Rstar. Col. (7).—Briefdescriptionofthe results. Col. (6).—Figurenumber,ifpictures arepresentedinthispaper. Col. (5).—Exposuretime(inseconds) forthe[Om]image. Col. (4).—Exposuretime(inseconds) fortheHa+[Nn]image. Col. (3).—SpectraltypeoftheW-Rstar,fromvanderHuchtetal. 1988. Col. (1).—vanderHuchtetal.’s1981catalognumberoftheW-Rstar. -12_) CCD ImagerySurveyofGalacticWolf-RayetStarsintheNorthernSky MR 110 MR 88 MR 87 MR 82 HD HD HD 168206 HD 165763 HD 165688 MR 80 MR 122 MR 111 MR 119 HD 214419 MR 114 NS 6 MR 112 HD HD MR 90 MR 89 HD 169010 LS 14 NS 4 HD 56925 HD 50896 HD 17638 HD 16523 HD 219460 HD 213049 HD 211853 HD 211564 HD 197406 HD 193077 HD 192641 HD 192103 HD 191765 MR 97 MR 96 MR 93 NaSt 1 DA 1 HD 9974 HD 6327 HD 192163 HD 190918 HD 190002 HD 187282 HD 186943 HD 177230 LS 15 CRL 2104 LSS 4368 HD 4004 ST LS 16 CRL 2179 Other Name ST 1 ST ST ST 2 209 BAG 195177 3 193928 193576 193793 © American Astronomical Society • Provided by theNASA Astrophysics Data System WC8+08-9IV ŒL Spec. WN7 WN8 WN7 WN9 WC9 WN4.5 WN7 WC6 WN6+0 WN5+08V WC5 WN6 WN7 WC4 WN7+WC4 WC5 WC5 WC5 WC9 WN6 WN7-8 WN8 WC9 WOl WN3 WC4 WN6 WN5+06 WC7+OB WN6 WC8 WN4.5+09Ib 600 WC6 WN10 WC9 WN7 WC9 WC10 WC8 WN8 WN6 WN4 W02 WC7+04-5 WN6 WN6 WN7 WN8 WN4 WN4 WN8 WN8 WN5 WC6 WC5 WN3 WN2 WN5 WN4+09.5V WC5 WC7 Type 1200 1200 1200 1200 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 600 300 600 900 600 600 600 600 300 600 600 600 600 600 600 600 600 600 600 (4) (5) Exposure TABLE 2 1200 1200 600 600 600 600 600 600 600 300 300 600 600 600 600 600 600 600 900 600 600 600 900 600 600 900 600 600 Figure Remarks (6) (7) probable ringnebula possible diffuseemission possible diffuseemission possible diffuseemission no nebulosity possible diffuseemission possible diffuseemission possible diffuseemission nebulosity around nebulosity around probable newringnebula nebulosity around no nebulosity no nebulosity no nebulosity nebulosity around no nebulosity no nebulosity no nebulosity no nebulosity no nebulosity no nebulosity no nebulosity no neulosity nebulosity around no nebulosity possible faintemission no nebulosity diffuse emissionaround nebulosity around probable newringnebula no nebulosity no nebulosity ring nebula;G2.4+1.4 ring nebula;NGC2359 no nebulosity no nebulosity possible ringnebula;S132 no nebulosity no nebulosity no nebulosity no nebulosity possible newringnebula ring nebula;$308 nebulosity around in nebulosity in nebulosity ring nebula;NGC6888 ring nebula;Anon(MRlOO) ring nebula;L69.8+1.74 ring nebula;Anon(MR95) ring nebula;Ml-67 faint nebularknots in nebulosity in nebulosity in nebulosity faint diffuseemission in nebulosity in nebulosity in nebulosity in nebulosity in nebulosity 19 93ApJS. . .85. .137M This lowexcitationisexpected innebulaephotoionizedby tions areneededtodetermine theexactnatureofthisnebula. such latespectraltypesofcentral stars,WC8+08-9IV. ionization front.Futurespectroscopic andkinematicobserva- curved aroundthestar.Thisbrightridgeisreminiscentof an than arealenhancementofsurfacebrightnessalongsmall runs roughlyalongastraightline,insteadofan arc interval ofradius,asexpectedfromashell.Thesouthernridge two segments,anarcinthenorthwesternquadrantand a fined byadrop-offofsurfacebrightnessatlargerradii,rather does notyieldanystrongindicationofathreedimensional different fromthoseofotherwind-blownbubblesorejecta narrow brightridgeinthesouth.Thenorthwesternarcis de- shell structure.The“ring”impressionismainlyderivedfrom shells aroundW-Rstars,suchasS308,NGC3199,and different nebularfeaturesastheringnebulae.Thesefivenew by Harten,Felli,&Tofani(1978);however,wehaveidentified ter 1983).Twooftheobjectshavebeensuggestedpreviously: that theformerimpliesaveryhighconfidenceleveland 6888. Actually,adetailedanatomyoftheringmorphology We measurearadiusof3!5fortheinnerring,whichcorre- inner ring.Ourfieldofviewistoosmalltocovertheouterarc. rings aredescribedbelow. WR 113(CVSer)byGonzález&Rosado(1984)and153 and 132,“possible”newringsaroundWR133153. tively; column(6)givesthefigurenumber,ifimagesarepre- sponds to2pcforadistanceofkpc(vanderHuchtetal. our Haimagerevealsgreaterdetailsofthestructure on thePalomarObservatorySkySurvey(POSS)E-plate,but 4' radiusandanouterarcat9'radius.Bothfeaturesarevisible latter barelyover50%confidencelevel(Chu,Treffers,&Kwit- We use“probable”and“possible”intheconventionalsense The filterisnotedabovetheupperrightcomer:“H”for Figure 1displaysthesingle-frameimages.TheimageofWR results. exposure timesintheHa+[Nn]and[Om]filters,respec- 140 scribed adoubleshellstructurearoundCVSer:aninnerringof region S54(Sharpless1959).González&Rosado(1984)de- north up,andeasttotheleft. Ha-b [Nii]filterand“O”forthe[Om]filter.Allpictureshave Hucht etal.’s(1981)catalognumberofthecentralW-Rstar. number abovetheupperleftcomerofeachpictureisvander Anon (MR100)aroundWR134andNGC6888 pictures arepresentedinFigures2and3(Plates12-15).The sented inthispaper;column(7)givesabriefdescriptionofthe van derHuchtetal.(1988);columns(4)and(5)givethe 1988). 1958), isembeddedinthenorthernedgeofbrightHn 108 isshownasanexampleof“possiblediffuseemission.” 136 aremoreextendedthanthefieldofview;theirmosaic No [Oin]emissionisdetected inourCCDimageofCVSer. The morphologyoftheinnerringaroundCVSerisvery CV Ser,amemberoftheOBassociationSerOB2(Roberts We find“probable”newringnebulaearoundWR113,116, Images withvisiblenebulositiesareshowninFigures1-3. © American Astronomical Society • Provided by theNASA Astrophysics Data System 3. NEWWOLF-RAYETRINGNEBULAE 3.1. WR113(HD168206;CVSer) MILLER &CHU tance of4.4kpc(vanderHuchtetal.1988),theradius bly duetothepatchyforegroundobscuration.Alargepatchof dusty featureisvisiblewithinthering,too.Ifweadoptadis- constant radius,3!8.Theincompleteringmorphologyisproba- to comparethe[Om]imageandHaimage.Thebrightest the northofring,beingpartalargerstructureseenon plate, butourHa+[Nn]imageresolvesthenarrowfilaments (Chu etal.1983). ring is~5pc,comparabletomostgalacticW-Rnebulae lines showscurvedfilamentsaroundWR132.Itisinteresting sistent withphotoionizationbythelatespectraltypeofWR emission isdetectedwithina15minuteexposure;thiscon- along thering.Thelong,straight,narrowridgeofemissionto the latespectraltypeofWR132;nostrong[Om]emissionis lar towhatisseeninNGC6888,andindicativeofshock WR 132.Ourhigh-resolutionCCDimageintheHa+[Nn] POSS plates,isprobablynotrelatedtoWR116.No[Om] The 4!2radiuscorrespondsto2.6pcatadistanceof2.1 kpc WR 133.Oursmallfieldofviewprecludesanyfurtherstate- plate isthefaintextensionofbrightarcthatcurvesaround two brightstarsnearthesouthwestcomerofpictureare excitation. Anotherindicationofashocknaturecomesfrom filament asfiducialpoints).Thiskindofdisplacementissimi- from thestarthanHapeak(usingstarsalong[Om] Ha emission—the[Om]peakemissionis2"-4"fartherout sion. Furthermore,the[Om]emissionisdisplacedfrom at 4'southeastoftheW-Rstar. Themorphologyofthisarcis information. phology seenonthePOSSE-plate andadditionalHavelocity (van derHuchtetal.1988). certain, thatWR133isresponsiblefortheshapingofthis arc. ment aboutthisnebulosity.Itispossible,butadmittedly un- arc directlytothesouthofWR133andnebulosityin stars. Atadistanceof4.4kpc,the7!6radiuscorrespondsto vicinity ofWR132,therearenoothercatalogedearly-type expected inaphotoionizednebulaaroundWC6star.The similar tothatofthesouthern rimoftheringaroundWR113. nebula isdiscountedbyChuetal.(1983),basedonthemor- “shell B”inSI32.However,itsidentificationasaW-R ring southeast quadrantofourCCDimage.NotseenonthePOSS shows alotofnebulosityinthevicinity,includingbright SAO 69257(aK0star)and69259(unclassified).Inthe [O in]emissioncomesfromaregionwithonlyfaintHaemis- 116, WN8. 10 pc. The “ring”aroundWR116consistsofthreearcsatroughly The nebulosityaroundWR116isvisibleonthePOSSE- On thePOSSE-platethereissomediffuseemissionaround WR 133isinacomplexenvironment,asthePOSSE-plate Our Ha+[Nn]CCDimageof WR153revealedasharparc Harten etal.(1978)suggestthatWR153isassociatedwith 3.5. WR153(HD211853;MR116) 3.3. WR132(HD190002;MR98) 3.4. WR133(HD190918;MR99) 3.2. WR116(ST1;AS306) Vol. 85 19 93ApJS. . .85. .137M Miller &Chu(see85,140) PLATE 12 © American Astronomical Society •Provided bythe NASAAstrophysics Data System 134 FIG. 2.—MosaicCCDimagesofAnon(MR100)aroundWR134 in {a)Ha+[Nn]and(b)[Om] fig. 2a H 19 93ApJS. . .85. .137M Miller &Chu(see 85,140) © American Astronomical Society •Provided bythe NASAAstrophysics Data System 134 FIG. 2b O PLATE 13 19 93ApJS. . .85. .137M PLATE 14 Miller &Chu(see85,140) © American Astronomical Society •Provided bythe NASAAstrophysics Data System 136 fig. 3.—MosaicCCDimagesofNGC6888aroundWR136in{a)Ha+[Nn]and(b)[Om] FIG. H 1993ApJS ... 85. Miller &Chu(see85,140) © American Astronomical Society •Provided bythe NASAAstrophysics Data System 136 FIG. lb O PLATE 15 19 93ApJS. . .85. .137M these filaments,buttheHaridges aredisplacedfromthe[Om] the westtonorthofWR134. ThereisanHacounterpartof tended area.The[Om]-bright, filamentaryarcextendsfrom ridges byasmuch2"-3"at somelocations.Seeparticularly tral properties.OurmosaicimagesofAnon(MR100) in with animagetubecamera,thearcofemissionwassocloseto placed componentsdifferinginbothmorphologyandspec- the starasshownonPOSSE-plate.However,Chuet al.’s Ha+[N ii]and[Om]lines (Fig. 2)coveramuchmoreex- dances, excitation,anddynamicsareneededtodeterminethe (1983) Haand[Om]imagesofthisnebulashowtwo dis- Crampton (1971),basedonthebrightarctosouthwest of blown bubbleorstellarejecta(Chu&Treffers1981). The by thebackgroundemission.Futureobservationsofabun- ing thephotoionizationnature. the southwestboundaryofringisdefinedbyadarkcloud ( MR95)Chuetal.1983)mayhavebeenbadlycontaminated background diffuseemissionsuperposedonAnon(MR95). The previouslargeapertureFabry-PerotobservationsofAnon photoionized Hnregion;thereisnoevidenceforawind- outside. Thesharpnarrowridgesofemissionaretheionization era (Chuetal.1983).OurnewCCDimagesshowclearlythat clear whethertheouteredgewasartificiallycutoffbycam- the circularboundaryoffieldviewthatitwasnotvery nature ofthisnebula. fronts onthesurfaceofdarkcloud.Thisnebulaisa images ofS308inHaand[Om](Miller1992). are verysimilartothoserevealedinrecentlyobtainedCCD indicating shockexcitation.Thesemorphologicalproperties filamentary in[Om]thanHa.Thefilamentsextend also resolvedthis12'longarc.Anon(MR95)appearsmore [O m]imagerevealedonlyfaint,diffusenebulosity,confirm- farther outthantheHaemission,andhaveasharpouteredge, only detectedthisnebulainbothHa+[Nn]and[Om],but ( Heckathom,Bruhweiler,&Gull1982).OurCCDimagesnot these fournebulae:Anon(MR95),L69.8+1.74, portant newinformationcanbeextracted.Belowwediscuss tance of3.5kpc(vanderHuchtetal.1988). much higherqualitythanthosepreviouslyavailablethatim- verify thisnature.The4'radiuscorrespondsto4pcatadis- ble thatthissharparcinHa+[Nn]representsanionization emission isdetected,butnosharpfeaturesareseen.Itpossi- front. Spectroscopicandkinematicobservationsareneededto Many dustyfeaturesareseennearWR153.Diffuse[Om] No. 1,1993NEBULAEAROUNDW-R 100), andNGC6888. In thepreviouslypublishedimagesofL69.8+1.74taken The ringnebulaaroundWR134wasfirstsuggestedby It canbeseenfromourCCDimagesthatthereisafaint Anon (MR95)waspreviouslydetectedonlyin[Om] Our CCDimagesoffourknownW-Rringnebulaehaveso 4. KNOWNWOLF-RAYETRINGNEBULAE © American Astronomical Society • Provided by theNASA Astrophysics Data System 4.3. WR134;Anon(MR100) 4.1. WR128;Anon(MR95) 4.2. WR131;L69.8+1J4 STARS INNORTHERNSKY141 will derivethedetectability of circumstellarandinterstellar ily bythelimitedsensitivityof availableinstruments.Belowwe that notallW-Rstarsaresurrounded byvisibleringnebulae. The apparentabsenceofring nebulaecouldbecausedprimar- presence ofejectedstellarmaterialcanbediagnosedby its and causesthefossilbubbletocollapse(D’Ercole1992). The rial (Estebanetal.1992). and RCW104containmixturesofstellarinterstellarmate- NGC 3199containmostlyinterstellarmaterial,andG2.4+1.4 are recognizedasshellsofstellarmaterial,NGC2359 and and thefossilbubbleissmall,orifheatconductiondominates shells couldmerge,iftheambientinterstellardensityis high cumstellar materialsweptupbytheW-Rwind.These two genitor atthemain-sequencestage,andasmallbubbleof cir- anomalous abundances,e.g.,NGC6888,RCW58,andMl-67 large fossilbubbleofinterstellarmaterialsweptupbythe pro- Clearly, abettermodelfortheX-rayemissionofNGC6888is rant, showingnoopeningswherestellarwindmayleak. reveals afaintnetworkofclosedloopsinthesoutheastquad- Lozinskaya (1983).However,our[Om]imageofNGC6888 sion istheweakest(Bochkarev1988),assuggestedearlierby crepancy, itwasproposedthattheremightbealeakageof that alargefractionofthisnebulaisejectedstellarmaterial. material, aW-Rstarshouldbesurroundedbytwoshells—a stripped off*theouterenvelopestoexposeCNOprocessed stellar windfromthesoutheastquadrant,whereHaemis- et al.’s(1977)wind-blownbubblemodel.Toexplainthisdis- wind-blown bubble;however,itsobservedX-rayluminosityis tected intheX-ray(Kähler,Ule,&Wendker1987;Bochkarev ties ofthesetwoarcs. needed. an orderofmagnitudelowerthanthatexpectedfromWeaver (Dufour 1989)ofNGC6888haveprovidedstrongevidence ments (Esteban&Vilchez1992)and[Om]/Haratioanalysis former andclumpyinthelatter.Recentabundancemeasure- the brightarcvisibleonPOSSE-plate.ThisHa-bright interesting tocomparetheabundancesandkinematicproper- is notdetectedinthe[Om]imageatall.WR134aWN6 ambient medium. ground starsalonganarrowHafilamentcanbeusedasfidu- the filamentat9!5northwestofWR134,wheretwoback- [O m]thaninHa+[Nn](Fig.3),beingfilamentarythe needed todeterminetheirrelation.Itwouldbeparticularly arc areassociatedwithWR134.However,furtherstudies other WN6stars,suchasWR141.Itispossiblethatboththe star. Low-excitationphotoionizednebulaeareseenaround emission comesfromclosertotheshockfrontmovinginto cial points.Thisisconsistentwithshockexcitation;the[Om] [O m]-brightfilamentaryarcandtheHa-brightamorphous 1988). TheX-rayemissionimpliesthatNGC6888mustbea Our surveyofnortherngalactic W-Rstarsshows,however, NGC 6888istheonlyW-Rringnebulathathasbeende- If W-Rstarsaredescendantsofmassivethathave The morphologyofNGC6888appearsquitedifferentin The othernebularcomponent,brightinHa,correspondsto 4.4. WR136;NGC6888 5. DISCUSSION 19 93ApJS. . .85. .137M 3 6 -6 -3 4 253/-6 _1 -6 5 Barlow, M.J.1982,inIAUSymp. 99,Wolf-RayetStars:Observations,Castor,J.I.,Abbott,D. C,&Klein,R.I.1975,ApJ,195,157 Abbott, D.C,&Conti,P.S.1987, ARA&A,25,113.Bochkarev,N.G.1988, Nature,332,518 the boundaryofS109;WR136,137,and138aremembers of ern borderofthisplate.TheothernineW-Rstarsarewithin in theroundHnregionL69.8+1.74,isisolatednearsouth- above theequatorcanbefoundonPlate200ofPOSS: WR and SI09regiontodemonstratethissituation. the ionizedgasisalonglineofsight,notinimmediate that theseW-Rstarsareindeedinsidetenuousmedium and vicinity oftheW-Rstars.WeusestarsinCygOBI lae wouldformanapparentparadox.However,itispossible ized gas.Iftheyarephysicallyassociated,thelackofringnebu- detected. case bubbleswouldhavetoolowasurfacebrightnesstobe lae couldhavebeenobscuredbytheforegrounddust.Twelve nebulosity indicatesareallowinterstellardensity,inwhich stars (WR001,002,003,004,005,106,108,117,119,129, patchy dustyfeatures,indicatingthatnebulosityorringnebu- (WR 107,110,111,112,114,120,121,123,126,147,149, the POSSE-platesaroundtheseW-Rstarstoinspectlarge- scale structureintheirenvironments.Seventeenofthesestars ble cannotbedetectedunlesstheradiusisover200pc. cm“. Foradensityof0.1cm'orlower,theinterstellarbub- cm~ pccanbereachedonlyiftheambientdensityexceeds0.5 would be\2rnlcmpc,wherenistheambienthydrogen nebulosity or“possibledifíuseemission.”Wehaveexamined a fractionalthicknessof0.1,thelargestemissionmeasure 131, 133,134,135,136,137,138,139,141,and142.WR131, few toatensparsecs,limitingemissionmeasureof25 the ambientinterstellardensity.Assumingthatall M shellwouldfadeawayataradiusof4pc.Foranexpansion number densityincmandristheradiuspc.Forasizeof material withinaradiusrhasbeencompressedintoshellwith around onlyasmallfractionofW-Rstars. ited detectorsensitivityweshouldseeejecta-typeringnebulae 142 only afewtimes10yr,whichissmallcomparedto expressed as35mr~(Ar/)~cmpc,wheremisthemass velocity of50-100kms,thedurationfordetectabilityis of theshell.Foralimitingemissionmeasure25cmpc,5 in M,ristheradiuspc,andAr/rfractionalthickness emission measure,alongtheinnerradiusofshell,canbe 138, and148)areinrelativelydust-freefields,thelackof shell. Assumingauniformshellforapproximation,thelargest able) outbursts,dependingontheevolutionaryhistoryofa been lostviaredsupergiantwindorLBV(luminousbluevari- 150, 151,154,155,156,and158)areinfieldswithdense, should havecompresseditscircumstellarmaterialintoathin W-R star(Humphreys1991).Ineithercase,thewind out ringnebulae. bubbles, andcompareittotheobservationsofW-Rstarswith- Q 10 yrforthelifetimeofaW-Rphase.Therefore,withlim- 0 q Reidel), 149 Physics, Evolution,ed.C.W.H.de Loore&A.J.Willis(Dordrecht:Chu,Y.-H.1981,ApJ,249, 195 Nearly 25%(10/41)ofallW-Rstarswithdeclinations About one-thirdofthestarssurveyedaresuperposedonion- Among the62WRstarssurveyed,29ofthemhaveeitherno The detectabilityofaninterstellarbubbleisdeterminedby The circumstellarmaterialaroundaW-Rstarcouldhave © American Astronomical Society • Provided by theNASA Astrophysics Data System MILLER &CHU REFERENCES NAG 5-1900. knowledges thesupportofNASAgrantsNAG5-1755 and to completeourobservationsofthenorthernhemisphere. G. J.M.wouldliketothankK.Yossforhishelpfulcom- initial andsupplementalobservingtimewhichhasallowed us these equipmentsthispaperwouldnotbepossible.Thanks the 1mreflector,J.R.Dickelforuseofhisinterference to acknowledgeL.Thompsonforbuildingafocalreducer for ments intheearlyversionsofthismanuscript.Y.H.C. ac- also totheDirectorofMountLagunaObservatoryforboth the Esteban forhiscarefulreviewofthispaper.Wewouldalsolike sion, J.A.Laffforhisassistanceinthedatareduction,andC. filters, andT.H.Trolandforloaninghisenlarger;without insufficient detectorsensitivity. absence ofringnebulaearoundmostW-Rstarscouldbedueto foreground obscuration,lowambientinterstellardensity,and explanation forthelowX-rayluminosityofnebula.The and 132,possiblenewringnebulaearoundWR133 lae. WefindprobablenewringnebulaearoundWR113,116, around W-Rstars,includingallpreviouslyknownringnebu- of-26°.BothHa+[Nn]and[Om]filtersare shows acompleteshell,whichcontradictsthe“leakybubble” used. Wepresentallsurveyimagesthatshownebulosities consist of62starsandrepresentacompletelistdownto around galacticW-Rstarsinthenorthernhemisphere,which the onlyringnebulaaroundamemberofCygOBI,NGC therefore, themembersofCygOBIarenotexpectedtobe probably shouldnotbeusedtostudythepropertiesofstellar 6888, containsstellarmaterial(Estebanetal.1992). surrounded byanyinterstellarbubblesindividually.Indeed, POSS platethatthediffusenebulositiesareactuallypartsofa ionization flux. detector sensitivity.Theirregularlyshapednebulaearound ground obscuration,lowambientinterstellardensity,and UV absorptionlinestudyshowsasupershellaroundCygOBI; not inringnebulae.Onalargerscale,itcanbeseenfromthe (Hiltner 1956).RingnebulaearepresentaroundWR134, W-R starsarelikelytobelocatedalongthelineofsight,hence stars isprobablycausedbythecombinationofunevenfore- absorption studiesintheUV(St-Louis&Smith1991).The Cyg OB1,andWR134135aremembersofOB3 structure alongthelineofsightcanbeseenininterstellar complex nebularstructure,andthecomplexityofinterstellar 153. OurnewmosaicimageofNGC6888inthe[Om]line 139, 141,and142aresuperposedondiffusenebulosity,but 136, andpossibly133.AsshowninFigure1,WR135,137, We wouldliketothankM.-M.MacLowforusefuldiscus- We havecompletedaCCDimagerysurveyofnebulae In summary,theabsenceofringnebulaearoundmostW-R 6. 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