Analysis of the WN star WR 102c, its WR nebula, and the associated cluster of massive stars in the Sickle Nebula

1.6 MB·

by  M. Steinke

Astronomy&Astrophysicsmanuscriptno.wr102c_arxiv (cid:13)cESO2016
February15,2016
Analysis of the WN star WR102c, its WR nebula, and the
associated cluster of massive stars in the Sickle Nebula(cid:63)
M.Steinke1,2,L.M. Oskinova1,W.-R.Hamann1,A.Sander1,A.Liermann3,andH.Todt1
1 InstituteofPhysicsandAstronomy,UniversityofPotsdam,14476Potsdam,Germany
e-mail:[email protected], [email protected]
2 I.PhysikalischesInstitutderUniversitätzuKöln,ZülpicherStraße77,50937Köln,Germany
3 LeibnizInstituteforAstrophysicsPotsdam(AIP),AnderSternwarte16,14482Potsdam,Germany
Received04November2015;accepted
6
1
ABSTRACT
0
2
Context.ThemassiveWolf-RayettypestarWR102cislocatedneartheQuintupletCluster,oneofthethreemassivestarclustersin

b theGalacticCentreregion.PreviousstudiesindicatedthatWR102cmayhaveadustycircumstellarnebulaandisamongthemain
e ionisingsourcesoftheSickleNebulaassociatedwiththeQuintupletCluster.
F Aims.ThegoalsofourstudyaretoderivethestellarparametersofWR102cfromtheanalysisofitsspectrumandtoinvestigateits
stellarandnebularenvironment.
2
Methods. We obtained observations with the ESO VLT integral field spectrograph SINFONI in the K-band, extracted the stellar
1
spectra,andanalysedthembymeansofstellaratmospheremodels.

Results.OurnewanalysissupersedestheresultspreviouslyreportedforWR102c.Wesignificantlydecreaseitsbolometricluminosity
]
R and hydrogen content. We detect four early OB type stars close to WR102c. These stars have radial velocities similar to that of
WR102c.WesuggestthattogetherwithWR102cthesestarsbelongtoadistinctstarclusterwithatotalmassof∼ 1000M .We
S identifyanewWRnebulaaroundWR102cintheSINFONImapofthediffuseBrγemissionandintheHSTPaαimages.TheBr(cid:12)γline
h. atdifferentlocationsisnotsignificantlybroadenedandsimilartothewidthofnebularemissionelsewhereintheHiiregionaround
p WR102c.
- Conclusions.ThemassivestarWR102clocatedintheGalacticCentreregionresidesinastarclustercontainingadditionalearly-type
o stars.ThestellarparametersofWR102caretypicalforhydrogen-freeWN6stars.WeidentifyanebulasurroundingWR102cthat
r hasamorphologysimilartoothernebulaearoundhydrogen-freeWRstars,andproposethattheformationofthisnebulaislinkedto
t
s interactionofthefaststellarwindwiththematterejectedatapreviousevolutionarystageofWR102c.
a
[ Keywords. stars:early-type–stars:individual:WR102c–stars:Wolf-Rayet–Galaxy:center–ISM:Hiiregions–infrared:stars

2
v
1. Introduction anobservational“smokinggun”inthesearchfornewWRstars
5
9 (Flageyetal.2011;Mauerhanetal.2011;Wachteretal.2010).
TheadventofIRobservationsledtothediscoveryofmanymas-
3 Barniskeetal.(2008)haveperformedananalysisofthenear-
3sive stars in the central part of our Galaxy, mainly congregated IR K-band spectrum of the Peony star by means of the non-
0inthreemassivestarclusters,butalsoscatteredinthefield(e.g.
LTEstellaratmospherecodePoWR(e.g.Hamann&Koesterke
.Figeretal.1999b;Homeieretal.2003).Therelativelyisolated
1 1998b;Gräfeneretal.2002).Ithasbeenshownthatthisobjectis
massivestarsintheGalacticCentre(GC)regionhavenotbeen
0 amongthemostluminous,andinitiallymostmassivestarsinthe
extensively observed and are as yet poorly understood (among
6 Galaxy.However,atthetimeoftheirpapergoodqualityspectra
1recentresults,seee.g.Dongetal.2015;Habibietal.2014;Os- of WR102c were not available and only crude qualitative con-
v:kinovaetal.2013). clusionscouldbemadeaboutthissource.
TostudytwosuchrelativelyisolatedWolf-Rayet(WR)stars,
i To remedy this situation and to study the Peony star and
XWR102candWR102ka(knownasthePeonystar),weobtained
WR102c in more detail, we obtained integral field spectra of
rmid-IRspectrausingtheIRSspectrographonboardtheSpitzer these stars and their nebulae with the Spectrograph for Integral
a
telescope(Houcketal.2004).Theseobservationsleadtothede-
FieldSpectroscopyintheNearInfrared(SINFONI).Inthepre-
tectionofdustycircumstellarnebulaearoundtheseobjects(Bar-
viouspaper(Oskinovaetal.2013,herafterPaperI)weanalysed
niske et al. 2008). This was an unexpected discovery, since it
the Peony star WR102ka and its surrounding. In this paper we
was previously believed that dust cannot survive in the imme-
concentrateontheanalysisofWR102c.
diate vicinity of hot stars of spectral type WN. However, since
WR102c is located in the neighbourhood of the Quintuplet
then,dustyIRnebulaehavebeendiscoveredaroundmoreWN-
Cluster,inalargeHiiregionseenintheIRimagesasextended
type stars (Gvaramadze et al. 2009, 2014; Burgemeister et al.
diffuse emission and called the Sickle Nebula (see Fig.1). The
2013).Evenmoreimportantly,suchdustynebulaehavebecome
starwasdiscoveredduringasurveybyFigeretal.(1999b),who
classified it as WN6 subtype. The goal of our present analy-
(cid:63) Thescientificresultsreportedinthisarticlearebasedonobserva- sis is to obtain the parameters of WR102c by means of spec-
tionsobtainedduringtheESOVLTprogram383.D-0323(A) tral modelling, and to unravel its evolutionary history and pos-
Articlenumber,page1of10
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Fig.1. HST imageoftheQuintupletClusterandtheSickleNebula.Imagesizeis4.(cid:48)4×2.(cid:48)9.ThehorizontalaxisisparalleltoGalacticlongitude.
ThenetPaschen-αimageisinred(seedetailsinDongetal.2011),theNICMOSNIC3F190Nimageingreen,andtheNICMOSNIC3F187N
imageinblue(continuumandlinefilterforPaα).ThewhiteboxaroundWR102cmarksthefieldofourSINFONImosaic.Thisfieldis≈1(cid:48)from
thecentreoftheQuintupletCluster,whichisseenasagroupofbrightbluestarsjustbelowtheimagecentreclosetothePistolNebula(identified
byitscharacteristicshape).TheimageisbasedonthedataobtainedinthePaschen-αsurveyoftheGalacticCentre(Wangetal.2010).
sible ties with the Quintuplet Cluster. We study the environ- The observations were performed with the integral field spec-
ment of WR102c by means of integral field spectroscopy to trographSINFONI(Eisenhaueretal.2003;Bonnetetal.2004)
searchforothermassivestarsthat,togetherwithWR102c,may yieldingathree-dimensionaldatacubewithtwospatialdimen-
formamassivedistinctsubcluster.Wealsostudythepartofthe sionsandonespectraldimension.TheK-band(1.95−2.45µm)
Sickle Nebula that is directly influenced by ionising radiation grating with resolving power R ≈ 4000 was used. The spatial
fromWR102c.Throughoutthepaperweadoptdistancemodu- scale was chosen as 0(cid:48).(cid:48)25 per pixel. The total observation con-
lusDM =14.5mag(Reid1993). sistsofamosaicofsevenpointings(observationalblocks),cov-
Special interest in WR102c is also motivated by the recent ering≈ 24(cid:48)(cid:48)×23(cid:48)(cid:48) (≈ 0.9pc×0.9pc)centredonWR102c(see
report by Lau et al. (2015) who have identified a dusty helix Fig.2).
shape filament in the vicinity of the Quintuplet Cluster. Lau
Theadaptiveopticsfacilitycouldnotbeusedsincethereis
etal.proposethatthisdustyfilamentisaprecessing,collimated no sufficiently bright reference star in the neighbourhood. The
outflowfromWR102c.Furthermore,ithasbeensuggestedthat
logoftheobservationsisgiveninTable1.ABBA(sciencefield
WR102chasagravitationallyboundcompactbinarycompanion
–sky–sky–sciencefield)cycleswereperformedateachpoint-
with an orbital period > 800days. This hypothesis potentially
ing.Eachfieldwasobservedwithatotalexposuretimeof300s,
makesWR102caveryrareandinterestingobjectthatdeserves
usuallyasthesumoftwodetectorintegrationsof150seach,ex-
athoroughstudy.
ceptforthefields361404and361410wherewehadtosplitthe
TheSINFONIobservationsanddatareductionarepresented
integrationsinto30sintervalstoavoidsaturationofthebright-
in Sect.2. The circumstellar nebula around WR102c is dis-
estobjects.Toobtainfluxcalibratedspectra,standardstarswere
cussedinSect.3.ThespectralanalysisofWR102cisdescribed
observedatsimilarairmassandinthesamemodeasthescience
in Sect.4. The objects detected near WR102c, in particular a targets.Theseeingwasbetween0(cid:48).(cid:48)6and1(cid:48).(cid:48)1,limitingtheangu-
subclusterofearly-typestars,arediscussedinSect.5,whilethe
larresolutionofourobservations.
summaryandtheconclusionsaredrawninSect.6.
The data reduction was performed with the SINFONI
pipeline version 2.32 (EsoRex version 3.9.6) using additional
cosmicremovalfromL.A.cosmic(vanDokkum2001)andself-
2. Observationsanddatareduction
writtentoolsinInteractiveDataLanguage(IDL).Theprocedure
The data used in this work were obtained with the ESO VLT was the same as performed for the Peony star and we refer to
UT4 (Yepun) telescope between April 29 and May 19, 2009. section2ofPaperIfordetails.
Articlenumber,page2of10
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Table1.Logofobservations.
Block Date R.A.(J2000) Dec.(J2000) sky1 Telluric Average
(ID) 2009 17h46m -28◦49(cid:48) standard seeing[(cid:48)(cid:48)]
361398 April29 11s.10 -0(cid:48).(cid:48)9 B1 HIP83861 1.05
361400 April29 10s.56 -0(cid:48).(cid:48)9 B2 HIP83861 0.98
361402 April29 11s.47 06(cid:48).(cid:48)3 B1 HIP83861 1.01
361404 May17 10s.93 06(cid:48).(cid:48)9 B2 HIP88857 0.64
361406 May17 10s.37 06(cid:48).(cid:48)3 B1 HIP85138 0.75
361408 May19 11s.51 14(cid:48).(cid:48)0 B2 HIP86951 0.57
361410 May19 10s.97 14(cid:48).(cid:48)0 B1 HIP84435 0.65
Notes.(1)skyfieldsB1andB2arecentredat17h46m18s.53,−28◦48(cid:48)5(cid:48).(cid:48)7and17h46m15s.46,−28◦48(cid:48)54(cid:48).(cid:48)2,respectively.
25
24
23
22
21
20
19 18
16
17
13 14 15 12 15
11
10
9
6 8 7
5
3 4
N N
2
E E
WR nebula
1 2" 2"
Fig.2. Imageofthecollapsedgrandcube(seetextfordetails).Thede- Fig.3. NegativeimageatthewavelengthoftheBrγ-line.Themaximum
tectedsources(opencircles)arelabelledwiththeirsequentialnumbers emission (darker areas in the false-colour image) is ≈ 2mJy/arcsec2
(seeTable2).Theimagesizeis23(cid:48).(cid:48)6×23(cid:48).(cid:48)1(0.92×0.90pc).Northis while the lowest emission (lighter areas) is ≈ 0.3mJy/arcsec2. The
upandeastistotheleft. bluearrowspointoutthepositionofthecircumstellarWR102c-nebula.
Source15(WR102c)isindicatedinthecentreofthenebulaasarethe
positions(smallcrosses)ofourextractedspectra(cf.Fig.4).
Theflux-calibratedthree-dimensionaldatacubesoftheindi-
vidualfieldswerecombinedtoagrandmosaiccube.Thiscube
was “collapsed”, i.e. summed over all wavelengths, to obtain 3. CircumstellarnebulaaroundWR102c
a pass-band image for the purpose of point source detection.
Our observations are sensitive down to an apparent magnitude Fromtheanalysisofmid-IRobservationsofWR102cwiththe
of K = 14.8mag. With the reddening towards WR102c (see Spitzer and MSX telescopes, Barniske et al. (2008) detected a
s
Sect.4), the extinction in the K-band amounts to about 3mag. dustycircumstellarnebulaheatedbytheintenseradiationofthe
Thus, at the distance of 8kpc, our observations are sensitive to WR star. However, the spatial resolution of these instruments
absoluteK-bandmagnitudes<−2.8mag. wasnotsufficienttodirectlyimagethisnebula.Ournear-IRSIN-
We securely detect 25 stellar point sources in the observed FONI data have a much better resolution. Hence, to study the
field (see Fig.2). Their coordinates, spectral types, and radial nebular emission we created a narrow band image in the Brγ
velocities are given in Table2. The K -band magnitudes were line.AbipolarorringstructurecentredonWR102c(source15)
s
calculatedfromtheflux-calibratedspectra,usingthe2MASSfil- isclearlyseeninthisimage(seeFig.3).Theradiusoftheneb-
tertransmissionfunction(Skrutskieetal.2006).Theradialve- ula is ≈ 4(cid:48)(cid:48) (0.15pc). As the field is quite crowded with stars,
locities were derived from the Doppler shift of prominent lines itisdifficulttoconcludewhetherthenebulaiscircularorbipo-
(except for WR102c, which has a wind-dominated spectrum), lar.Tomeasureitsexpansionvelocity,thespectrawereextracted
namely the first 12CO band heads for cool stars and hydrogen at different locations. As can be seen in Fig.4, the nebular Brγ
Brγ and helium lines for the OB-type stars. Further details are linesareneithershiftednorbroadenedbymorethan≈80kms−1
giveninSects.4and5. (SINFONI’sspectralresolution).Thisupperlimitontheexpan-
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Table 2. Catalogue of stellar sources detected in the observed field
(within≈0.9pc)aroundWR102c
No. R.A. Dec. K MK (cid:51)
s rad
17h46m −28◦49(cid:48) [mag] type [kms−1]
1 11s.65 17(cid:48).(cid:48)8 12.8 M0 -70 South west
2 11s.38 14(cid:48).(cid:48)9 13.0 M1 95
3 11s.29 13(cid:48).(cid:48)2 14.4 K1 -90
4 11s.20 13(cid:48).(cid:48)1 14.4 K4 85
5 10s.94 10(cid:48).(cid:48)8 13.4 M0 55
6 11s.34 10(cid:48).(cid:48)3 13.0 M0 50
7 10s.29 10(cid:48).(cid:48)3 14.3 K5 10
8 11s.07 10(cid:48).(cid:48)1 14.0 K4 205 set North
9 10s.58 09(cid:48).(cid:48)7 13.4 M0 60 ff
o
10 10s.88 08(cid:48).(cid:48)7 10.3 M5-6 -45
+
11 11s.69 08(cid:48).(cid:48)3 13.3 K5 140
x
12 10s.55 07(cid:48).(cid:48)9 12.4 M1 100 u
l
13 11s.67 07(cid:48).(cid:48)7 12.0 B1-2 100 f

14 11s.26 07(cid:48).(cid:48)7 14.1 B5 90 ve
15 11s.08 07(cid:48).(cid:48)5 11.6 WN6 120 ti
a
16 11s.53 05(cid:48).(cid:48)8 12.0 K0 120 l
e
17 11s.00 05(cid:48).(cid:48)3 12.6 B2: 70 R West
18 10s.93 05(cid:48).(cid:48)2 14.3 K3 270
19 11s.13 04(cid:48).(cid:48)8 13.8 K5 90
20 10s.84 04(cid:48).(cid:48)5 14.8 K5 -250
21 10s.91 03(cid:48).(cid:48)2 14.7 M0 185
22 11s.28 02(cid:48).(cid:48)9 14.0 M0 0
23 10s.64 00(cid:48).(cid:48)6 13.8 K4 -65 East
24 10s.54 -1(cid:48).(cid:48)0 14.0 K2 -35
25 10s.85 -2(cid:48).(cid:48)6 12.8 O7? 100
sionvelocityindicatesthatthenebulaisnotexpandingquickly,
oppositetowhatwouldbeexpectediftheobservedbipolarstruc-
tureweretheresultofafastcollimatedoutflow. -800 -400 0 400 800
Nebulae with various morphologies are often observed v in km/s
around WR stars. The mechanisms of nebula formation are rad
linkedtostellarevolution:whenamassivestarleavesthemain
Fig. 4. Observed Brγ line in the spectrum of the WR102c-nebula at
sequence,itlosesalargeamountofmatter.Intheluminousblue
differentstar-freelocations.Thespectra(aslabeled)weretakenatthe
variable(LBV)oraredsupergiant(RSG)phasethestellarwind following distance and direction from WR102c east at 4(cid:48)(cid:48) (0.15pc),
isdenseandslow,whileatalaterevolutionarystages(WN)the westat3(cid:48)(cid:48) (0.11pc),northat10(cid:48)(cid:48) (0.38pc)south-westat6(cid:48)(cid:48) (0.23pc),
wind is fast. The interaction between the slow and fast moving cf.Fig.3forthepositions.
windcreatesshellsthatareionisedandheatedbythestellarradi-
ation(e.g.Garcia-Segura&MacLow1995;Freyeretal.2006;
van Marle et al. 2007; Toalá & Arthur 2011). A recent review can,perhaps,beattributedtotheverydenseandwarmenviron-
on WR nebulae is given in Toalá et al. (2015) and references ment in the vicinity of the Quintuplet Cluster. Another unusual
therein. aspect is the presence of a helix-like tail likely associated with
To explain the nature of the nebula around WR102c seen WR102casfoundbyLauetal.(2015).
in the Brγ image we considered the following check-list. The TheWR102c-nebulaandhelixtailcanalsobeclearlyrecog-
nebula is surrounding a WR-type star. It has a small expansion nised in the HST Paα image (Fig.5). Moreover, it appears that
velocitysimilartootherWRnebulae(e.g.Marstonetal.1999). another helix-like outflow is seen within the ring-nebula, as in-
The nebula is clearly seen from its hydrogen emission (in this dicatedinFig.5.However,thePaαimagesshouldbeinterpreted
casePaαandBrγ)andinHeimapsofdiffusegas,analogously with caution. These were heavily processed, as explained in
tootherWRnebulae.Significantly,WRnebulaehavemorpholo- depthinDongetal.(2011).TheSINFONIimagesdonotshow
gies that correlate with the spectral type of their central stars. obvioushelix-likestructuresassociatedwithWR102c.
Theringorbubble-likemorphologies(B-type),sometimesbipo- Vink et al. (2011) have found a significant correlation be-
lar, are found around WNE stars with fast winds, just as in the tween fast rotating WR stars and the subset of WR stars with
caseofWR102c.Thesecharacteristicsleadustoconcludethat ejecta nebulae. They note that these objects have only recently
thenebulaaroundWR102cisatypicalWRnebula. transitioned from a previous RSG or LBV phase and thus have
However, there are some important aspects that distinguish notyetsignificantlyundergonespin-downwhichwillbecaused
the WR102cnebula. It is small, only0.15pc, while the typical bytheirintensivemasslossduetotheconservationofmomen-
sizeofWRnebulaeisafewparsec.Thesmallsizeofthisnebula tum.ThissubsetoffastrotatingWRstarsarethecandidateγ-ray
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M.Steinkeetal.:AnalysisofWR102canditsclusterintheSickleNebula
WR-nebula
Helix-shape outflow (?) Fig. 5. HST Paschen-α image (Dong et al.
2011)oftheringnebulaaroundWR102c.The
legends and the arrows indicate (i) the helix-
like nebulosity detected by Lau et al. (2015);
(ii) the ring WR nebula as seen in the SIN-
FONIBrγimageinFig.3;(iii)asmallstructure
thatresemblesahelix-likeoutflow.Thedashed
rectanglecorrespondstoourSINFONImosaic
WR102c outflow? field. The orientation is the same as in Figs.2
and3,i.e.northisupandeastistotheleft.The
image is a zoom into the Paschen-α survey of
theGalacticCentre(Wangetal.2010).
burstprogenitors.Gräfeneretal.(2012)haveidentifiedaninci- ringtotheradiusR .Forthewindvelocityweadopttheusualβ-
∗
dencerateof∼ 23%forWRstarsintheGalaxythathavepos- lawwithβ=1(e.g.Sanderetal.2015).Eachstellaratmosphere
sibleejectanebulaeandrotatefasterthantheaverageWRstars. modelisdefinedbyitseffectivetemperature,surfacegravity,lu-
Theynotethatevenearly-typehydrogen-freeWRstars,suchas minosity, mass-loss rate, wind velocity, and chemical composi-
WR6 (WN4) and WR136 (WN6) can be fast rotators, perhaps tion. The gravity determines the density structure of the stellar
evolvingthroughbinarychannels.Hence,thepresenceofacom- atmospherebelowandclosetothesonicpoint.Iflinesfromthe
pactbipolarnebulaandahelix-likeoutflowfromWR102cmay quasi-hydrostaticlayersarevisibleinthespectrum,theanalysis
indicatethatthisobjecthasonlyrecentlytransitionedtotheWR allowsthegravityandthusthestellarmasstobederivedfromthe
evolutionarystage,andisstillarelativelyfastrotator. pressure-broadenedabsorptionlineprofiles(Sanderetal.2015).
ForagivenchemicalcompositionandstellartemperatureT ,
∗
syntheticspectrafromWRmodelatmospheresofdifferentmass-
4. TheWN6starWR102c lossrates,stellarradii,andterminalwindvelocitiesyieldalmost
the same emission-line equivalent widths if their transformed
WR102cwasdiscussedinBarniskeetal.(2008)whoconfirmed
its spectral type as WN6 based on the inspection of the low- radii Rt ∝ R∗(cid:104)(cid:51)∞D−1/2M˙−1(cid:105)2/3 (Schmutz et al. 1989) agree.
resolutionspectrumshownbyFigeretal.(1999b).Inthepresent To account for small-scale wind inhomogeneities, we adopt a
paper,wenowanalysethenewhigh-qualitySINFONIspectrum clumping contrast of D = 4 as a typical value for WN stars
ofWR102cindetaillargelyrevisingtheestimatesmadeinBar- (Hamann&Koesterke1998a).WenotethatR isinverselycor-
t
niskeetal.(2008). related with the mass-loss rate, i.e. the smaller the transformed
The WR102c spectrum (Fig.6) was analysed by means of radius,thehigherthedensityinthestellarwind.
PoWR model atmospheres1 (Hamann & Gräfener 2004; Todt
etal.2015).ThePoWRcodehasbeenusedextensivelytoanal-
ysethespectraofmassivestarsintheIRaswellintheultravio- 4.1. TemperatureofWR102c
letandopticalrange(e.g.Oskinovaetal.2007;Liermannetal.
Figure6showsthenormalisedspectrumofWR102ccompared
2010; Oskinova et al. 2011; Sander et al. 2012; Hainich et al.
to synthetic spectra. Unfortunately, it is impossible to find a
2014). The PoWR code solves the non-LTE radiative transfer
model that simultaneously fits all Hei and Heii emission lines.
in a spherically expanding atmosphere simultaneously with the
The model for T = 75kK reproduces the Heii emission lines
statistical equilibrium equations and accounts at the same time ∗
perfectly,buttheHeilinesat2.06µmand2.11µmareseverely
for energy conservation. Complex model atoms with hundreds
underestimated(reddottedlineinFig.6).Thealternativemodel
of levels and thousands of transitions are taken into account.
drawn as a green dashed line for a temperature of T = 66kK
The computations for the present paper include detailed model ∗
reproducestheHeilineat2.06µmperfectly,butunderestimates
atomsforhydrogen,helium,carbon,oxygen,nitrogen,andsili-
someoftheHeiilines.Thelineat2.11µmisactuallynotonly
con.Ironandiron-groupelementswithmillionsoflinesarein-
composedofHei,butisalsoblendedwithNiii.Thecorrespond-
cludedthroughtheconceptofsuper-levels(Gräfeneretal.2002).
ing transitions are not fully included in our atomic data, which
Theextensiveinclusionoftheirongroupelementsisimportant
becauseoftheirblanketingeffectontheatmosphericstructure. mightexplainthemismatch.
Hence,thestellartemperatureremainsuncertainintherange
The stellar radius R , which is the inner boundary of our
∗ T = 66kK to 75kK. Moreover, if the star is a fast rotator it
model atmosphere, corresponds by definition to a Rosseland ∗
could lead to variations of the wind properties between poles
continuumopticaldepthof20.ThestellartemperatureT isde-
∗
andequator.
finedbytheluminosityandthestellarradiusR viatheStefan-
∗
Boltzmann law; i.e. T denotes the effective temperature refer- It is not possible to establish the rotation rates of WR stars
∗
fromspectroscopicanalysisofthenear-infraredonly.Forexam-
1 http://www.astro.physik.uni-potsdam.de/PoWR/ ple,ourtestcalculationsshowthateventheunrealisticallyhigh
Articlenumber,page5of10
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1.6
WR 102c
1.4
1.2
x
u
l
F1.0

d
e
z
i
al0.8
m
Nor000...246 HeII 15-8 1o1PS - 2sHeI 2p o22D - 3pPCIV 3d HeII 26-9NV 11 - 10o33S - 3pPHeI 4so11S - 3pPHeI 4sNIII 8-7 HeI 7 - 4HeII 14-8(Br)γHeII 10-7 HeII 22-9 22P - 5sSNIII 5pHeII 21-9NV 5p - 5s HeII 20-9 o22D - 9pPIV 10dHeII 13-8 HeII 19-9
C
2.0 2.1 2.2 2.3 2.4
λ / µm
Fig.6. NormalisedK-bandspectrumofWR102c(solidblue),comparedtotwoPoWRmodels:T = 75.0kK,logL/L = 5.57,logM˙ = −4.17
∗ (cid:12)
(reddottedline);T =66.0kK,logL/L =5.51,logM˙ =−4.08(greendashedline).Theprominentspectralfeaturesareidentified.
∗ (cid:12)
photosphericrotationvelocitiesupto(cid:51) sini = 1000kms−1 > otherwise carbon emission lines would be visible (e.g. Civ at
rot
(cid:51) wouldnotleaveanynoticeableimprintontheK-bandspec- λ = 2.07−2.08µm). Hence, we set the carbon abundance to a
crit
trum as long as the wind does not corotate (see discussion in massfractionof10−4.
Shenar et al. 2014). We do not observe signs of such extreme
windcorotationinWR102c.
4.3. BolometricluminosityofWR102c
Fortunately,theimpactoftheT uncertaintyontheimplied
∗
mass-loss rate and luminosity is relatively small (see Table 3).
Inparticular,theeffectonT ,i.e.theeffectivetemperaturere- Table3.StellarparametersofWR102c
2/3
ferring to the radius of Rosseland optical depth τ = 2/3, is
Ross
hardly affected. This invariance reflects the parameter degener-
Spectraltype WN6
acyofverydensestellarwindsasdiscussedine.g.Hamannetal.
logL/L 5.5...5.7
(cid:12)
(2006).
T [kK] 66...75
∗
Anotherspeculativeexplanationfortheinconsistentspectral T [kK] 33...37
2/3
fit could be the presence of a cooler, unresolved companion. A logM˙ [M yr−1] −4.17...−4.09
(cid:12)
useful empirical diagnostic of WR-binaries is provided by X- log Φ [s−1] 49.0...49.3
Ly
ray observations. While single WR stars are relatively faint X- (cid:51) [kms−1] 1600
∞
raysources(Ignaceetal.2000;Oskinovaetal.2003),theWR-
M /M ∼40
ini (cid:12)
typebinariesusuallydisplaycollidingwindphenomenaandare (cid:51) [kms−1] 120±40
bright,detectableX-raysourcesevenintheGCregion(Law& rad
A [mag] 2.8
Yusef-Zadeh2004;Oskinova2005).WR102cwasnotdetected K
in deep X-ray surveys of the Quintuplet Cluster (Wang et al.
2006).Thisnon-detectionprovidesevidenceagainstthebinarity
Intheirdiscoverypaper,Figeretal.(1999b)assignedaK -
hypothesis. s
band magnitude of 11.6mag to WR102c. This value was re-
vised by Barniske et al. (2008) who erroneously used the K -
s
4.2. Abundances bandmagnitudeofanearbybrightstar(source10inFig.2)from
the 2MASS and the Spitzer IRAC point source catalogues and
Barniske et al. (2008) constrained the hydrogen abundance in adopted K = 9.3mag for WR102c. This resulted in an over-
s
WR102c as being below 20% by mass. The new data allow estimatedstellarbolometricluminosity.ThenewSINFONIdata
this limit to be adjusted to < 5%. If the hydrogen content allowustounambiguouslyidentifyWR102cinthenear-IRim-
werehigher,itwouldcontributesignificantlytotheemissionat age (source 15 in Fig.2) with K =11.6mag, in agreement with
s
λ=2.16µm(Heii+Brγ).Thus,ournewanalysisconfirmsthat theoriginalreport.
WR102cisavirtuallyhydrogen-freeWNEstar. Toputstrongconstraintsonthestellarluminosity,wecom-
In the observed spectrum, all clearly detectable metal lines pared the model stellar spectral energy distribution (SED) with
(ofnitrogenandcarbon)areblendedwithheliumlines(e.g.Nv the available photometric and spectrophotometric data. The re-
at λ2.1µm or Civ at λ2.08µm). For our models we adopted a sult is shown in Fig.7. We used the available photometry of
massfractionof1.5%fornitrogen,whichistypicalforGalac- WR102cfromSpitzerIRAC(Churchwelletal.2009),UKIDSS
tic WN stars. The carbon abundance is constrained to (cid:28) 1%, (Lucas et al. 2008), and HST NICMOS (Dong et al. 2011).
Articlenumber,page6of10
M.Steinkeetal.:AnalysisofWR102canditsclusterintheSickleNebula
The SED fitting then allows the luminosity and the interstel- confirmed binaries (Tuthill et al. 2006). The importance of bi-
lar extinction to be adjusted by adopting the distance modulus nary channels in the evolution of massive stars is well recog-
of DM = 14.5mag. The observed photometry of WR102c is nised(e.g.Vanbeverenetal.2007).Schneideretal.(2014)used
nicely reproduced by a model with a bolometric luminosity of their binary evolution code to model the observed present-day
logL/L ≈ 5.6andtheextinctionE = 8.0mag,correspond- massfunctionsoftheQuintupletClusterandestimateditsageas
(cid:12) B−V
ing to A ≈ 2.8mag. The alternative, slightly cooler model 4.8±1.1Myrifbinarychannelsareincluded.Hence,withinthe
K
(T = 66kK) leads to logL/L ≈ 5.5 and the same extinction. uncertaintiestheageofWR102ciscomparabletotheageofthe
∗ (cid:12)
ThisA isconsistentwithWR102cbeinglocatedintheGCre- QuintupletCluster
K
gion(e.g.Schultheisetal.1999;Figeretal.1999a). WR102cislocated≈2.5pc(≈1(cid:48))fromthecoreoftheQuin-
WR102c is highly reddened and, if present, anomalous ex- tuplet Cluster. It is quite common for a massive star in the GC
tinction may lead to an uncertainty in the estimates of stellar to reside outside of the three known large clusters (e.g. Cotera
luminosity.Toinvestigatethisproblemwedidathoroughcheck etal.1999;Mauerhanetal.2010;Dongetal.2011).Thereare
of the various reddening laws using R and E provided by different scenarios that can explain the origin of these isolated
V B−V
the extinction functions of Moneti et al. (2001), Cardelli et al. massive stars, for example they might have been born in rela-
(1989),andFitzpatrick&Massa(2009).Wefoundthatthespec- tiveisolation,orejectedortidallystrippedfromoneofthethree
tral energy distribution is best reproduced by an extinction of known clusters, or they might belong to clusters that have not
E(B−V) = 8.0±0.3mag using the Moneti et al. (2001) and beendiscoveredyet.
Cardellietal.(1989)functions,whileE(B−V)=8.7±0.4mag It has recently been suggested by Lau et al. (2015) that the
fitsbestfortheFitzpatrick&Massa(2009)function,resultingin evolutionofWR102cmayhavebeenaffectedbybinaryinterac-
theuncertaintyintheluminositylogL/L =5.5...5.7. tions, and the star could have been ejected from the Quintuplet
(cid:12)
As a next step, we varied the R from the commonly used Cluster.However,basedonouranalysisthemeasuredradialve-
V
valueR =3.1by+0.5and+1.0foreachofthethreeextinction locity of WR102c is not outstanding and compares well with
laws. TVhe curves were then scaled in luminosity to match the theaverageradialvelocityoftheQuintupletstars(≈110kms−1,
K-band photometry. However, in all cases the reddening using Liermannetal.2012).Propermotionobservationsarerequired
the standard value R = 3.1 provides the best description of toestablishtherunawaystatusofWR102c.Ontheotherhand,
V
thestellarSEDandmatchesthephotometrymarksbetter.Thus, Habibi et al. (2014) used their N-body simulations and showed
we conclude that there are no reasons to suspect an anomalous thatupto80%oftheisolatedobservedWRstarsintheGCre-
reddeningforWR102c. gioncouldbeexplainedbytidalstriping.Inparticular,theyesti-
Our models predict that WR102c produces log(Φ ) = matetheageoftheQuintupletClusterto5Myrandshowthatthe
Ly projectedtidalarmsofthisclustermayextendoutto60pcinthe
49.0...49.3 [s−1] hydrogen ionising photons. This compares
directionoftheSagittariusB2region.GiventheageofWR102c
well with the value of 49.45 derived from radio observations
anditsproximitytotheQuintupletCluster,tidalstrippingisable
of the Sickle Nebula by Lang et al. (1997). Thus, although our
toexplainthelocationofWR102c.
revised number of ionising photons is lower than the value of
There is, however, another possible evolutionary path for
Barniskeetal.(2008),WR102ccanstillbeconsideredthemain
WR102c.OurSINFONIdatarevealedfourOB-typestarswithin
ionisingsourceoftheSicklenebula.However,thePaα-imageof
a projected distance of 1 pc around WR102c (see Sect.5).
theGCregion(Fig.1)doesnotshowafullyionisedholearound
Hence, it is possible that WR102c was formed together with a
WR102c,incontrasttotheregionaroundtheQuintupletCluster.
its own cluster, independently from the Quintuplet Cluster (see
ThiscouldmeanthatourWRstarislocatedintheforegroundof
Sect.5.3).
theSicklenebula.
5. StarsinthevicinityofWR102c
4.4. EvolutionarystatusofWR102c
5.1. Early-typestars
Thederivedstellarluminosityandtemperatureallowustoeval-
uate the evolutionary status of WR102c. In Figure8 the posi- Amongthe25stellarsourcesdetectedinourSINFONIobserva-
tionofWR102cintheHRdiagramiscomparedwithevolution- tions, we found four early-type stars (see Table2). All of these
ary tracks from Ekström et al. (2012) for rotating stars of solar objectshavecounterpartsintheUKIDSSGalacticPlaneSurvey
metallicity. WR102c is nicely located at the position of WNE (Lucasetal.2008);thecross-identificationsareprovidedinTa-
stars on a track with an initial mass of 40M(cid:12). In the case of a ble4.
rotatingmodel,theageofWR102cis<∼ 6Myr,whileassuming The K-band spectra of these early-type stars are shown in
evolutionwithoutrotationwouldyield<∼ 4Myr.Bothestimates Fig.9.Theradialvelocitiesmeasuredforeachstarareconsistent
assumesinglestarevolution.Withitsestimatedageof4−6Myr, with WR102c within the uncertainties. The extinction to each
WR102cwouldhavecompletedatleastoneorbitaroundtheGC early-typestarwasestimatedfromSEDfitting,andwasfoundto
(Stolteetal.2014). besimilartotheextinctiontowardsWR102c.Thus,weconclude
Assuming single star evolution and taking into account the thattheearly-typestarsintheWR102cfieldarelikelyspatially
ratios between numbers of stars with different spectral types, relatedandmightevenbegravitationallybound.
Liermann et al. (2012, 2014) constrained the age of the Quin- Forthespectralclassification,weusethenear-IRspectralat-
tupletClusterto3±0.5Myr.ItwasnoticedthatallWNstarsin lasofOBstars(Hansonetal.1996,2005).Source25iseithera
theQuintuplethavelatespectraltypes(WN9h)andallWCstars lateO-orearlyB-type(super)giant.Theotherthreeobjectsare
have WC8-9 spectral types (Liermann et al. 2009). The evolu- B-typestars.TheyhardlyshowanyfeaturesintheK-bandexcept
tionarychannelsthatleadtotheproductionoflateWCstarsare forhydrogenBrγandoneortwoHeilines(atλλ2.06,2.11µm).
not yet understood (see extensive discussion on this subject in Moreover, Brγ is contaminated by nebula emission. To over-
Sanderetal.2012).TheWCstarsintheQuintupletareseverely come this contamination, we subtracted the background emis-
enshroudedbydust(Monetietal.2001),andsomeofthemare sionfromthestellarspectra.Therefore,itisdifficulttodetermine
Articlenumber,page7of10
A&Aproofs:manuscriptno.wr102c_arxiv
-14.0
-14.8
o-1-2 A]m-15.2
o-1]A--1144..84 HST NICMFO1S87N11.3 -1 cflog [erg sλ--1165..06 FWigR.1072.c.TShepercetdrdaelneednesrpgeyctrudmistorifbtuhteioPnoWfoRr

-2m F190N 111111...666 4.1 4.3 log 4λ. 5/ Ao 4.7 4.9 model with T∗ = 75kK is shown as a red
c 111222...333 solidline(seeTable3forthedetailedparame-
-1s-15.2 ters)andcomparedtotheavailablephotometry,
[erg 111333...444 999...333777 888...777000 w(HhSicThNisIiCnMdicOaStedPabαybfilluteer(sUaKnIdDSSpSi)tzaenrdIbRlaAcCk
fλ Channels 2 and 3) boxes. The inset in the up-
g -15.6 perrightcornershowsthecontinuumphotome-
o
l trymarkscomparedtothecontinuumSEDfor
the two alternative models used in Fig.6 with
111666...111
-16.0 T = 66kK (green dashed curve) and 75kK
∗
(redsolidcurve),respectively.TheoverallSED
J H K C D
s fitishardlyaffectedbythetemperatureuncer-
UKIDSS Spitzer IRAC
-16.4 tainty. We note that in the mid-IR the stellar
SEDisbelowthephotometricobservation,at-
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 tributedtotheemissionfromawarmdustyneb-
log λ / Ao ula(Barniskeetal.2008).
T /kK
6.0 200 150 100 60 *40 20 10 HeI HeI HeI HI (Br)γ #25
pre-WR WNL WNE WC 2.5
et
s
f
of #17
40M + 2.0
x
WR102c u
5.6 m. fl #14
r1.5
o
n
#25
27M #13
1.0
)
L 2.1 2.2 2.3
/L5.2
λ / µm
(
g
lo #13 Fig.9. SINFONIspectraofearly-typestarsintheWR102cfield.The
18M numberaboveeachspectrumcorrespondstothesourceidentificationin
Fig.2andTable2.
#17
4.8 15M
We have determined the stellar parameters of the OB-type
starsintheWR102cclusterwithtentativefitsoftheSEDandthe
13M
#14 linespectratoPoWRmodels.TheresultsarecompiledinTable
He-ZAMS ZAMS 5.Theirinitialmasseswereestimatedfromthecomparisonwith
4.4 evolutionarytracksinthetheHRdiagram(seeFig.8).
5.5 5.0 4.5 4.0
log (T /K)
*
Table4.Cross-correlationsinWR102cclusterwiththeUKIDSScata-
Fig.8. HRdiagramwithevolutionarytracksofEkströmetal.(2012)
logue.SourcenumbersrefertoTable2
forrotatingstarsofsolarmetallicity.Thedifferentcoloursidentifythe
differentstagesofthestellarevolution:thinblack:pre-WRphase;thick
yellow: WNL phase (i.e. with hydrogen between 40−5% mass frac- SourceNo. IDfromUKIDSScatalogue
tion);thickgreen:WNEphase(hydrogenlessthan5%massfraction);
#13 J174611.81-284906.5
thickblue:WCphase(i.e.carbonmorethan20%massfraction).The
#14 J174611.34-284906.9
positionsofWR102c(bluediamond)andtheOB-typestars(lightblue
#17 J174611.03-284903.9
squares)areindicatedaswell.
#25 J174610.87-284856.6
theirspectralsubtypes.Nevertheless,fromthewingsofBrγtheir
luminosityclassescouldbeconstrained.
Articlenumber,page8of10
M.Steinkeetal.:AnalysisofWR102canditsclusterintheSickleNebula
Table5.StellarparametersoftheOBstarsinthesample early-type stars in this region (∼ 100kms−1). The position of
star10intheHRDwouldplaceitonatrackforaninitialmass
SourceNo. #13 #14 #17 #25 of9M(cid:12).Suchastarwouldrequiremorethan10Myrtoevolve
totheRSGphase.
Spectraltype B1-3V: B?III: B2:III? O9:I:
logL/L 5.0 4.5 4.8 5.4 Thus, we believe that, like other late-type stars in our SIN-
(cid:12)
T [kK] 20 24 20: 31: FONIfield,star10doesnotbelongtotheWR102ccluster,but
∗
M [M ] 18: 13: 15 27: insteadrepresentsapreviousepisodeofstarformationintheGC
ini (cid:12)
(cid:51) [kms−1] 100 90 70 100 region. This is similar to the conclusion reached by Liermann
rad
A [mag] 2.8 2.9 2.9 2.9 etal.(2012)fromtheiranalysisoftheQuintupletCluster.
K
Notes.ThesourcenumbercorrespondstoTable2.Acolonfollowinga
valueflagsitasuncertain.Theradialvelocitieshaveanuncertaintyof 99..9933
±40km/sduetothelimitedspectralresolution. -14.4 1100..7733
1111..8844 88..6699
5.2. Late-typestars o-1]A-14.8
Inadditiontotheearly-typestars,manypointsourceswithlate- -2m 88..6622
c
ttyimpeatsepdecfrtoramartehepreeqseunivtailnentthewfiidetlhd.oTfhtehetem12pCeOrat(u2r-e0s)wbearnedeas-t -1 erg s-15.2 88..1166
2ba.3siµsmwfeoldloetwerinmginGeodntzháeleszp-eFcetrrnaálntdyepzese.tTalh.e(2l0u0m8i)n.oOsnitythcelsaasmsees [log fλ-15.6 77..5500
were ranked on the basis of the CO index (Blum et al. 1996,
1155..5588
2003).TheextinctionwasobtainedfromcomparisonofMARCS
J H K A C D E
models(Gustafssonetal.2008)withthemeasuredphotometric s
-16.0
values in the infrared (Lucas et al. 2008; Ramírez et al. 2008; 2MASS Spitzer IRAC
Churchwell et al. 2009; Dong et al. 2011). The distance modu-
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9
luswastheninferredfromthisextinctionbycomparisonwiththe log λ / Ao
curvespublishedbySchultheisetal.(2014),whichthenalsoim-
Fig. 10. Spectral energy distribution (SED) of star 10 (MSX6C
pliestheluminosity.Theparametersoflate-typestarsaregiven G000.1668-00.0434)fittedbyaMARCSmodel(redcurve)withT =
∗
inTable6. 3.3kK, logL/L = 3.65, and logg = 1.0. The boxes represent pho-
(cid:12)
tometry from 2MASS J, H, and K (blue, labels = magnitudes), HST
Table6.Thelate-typestarsinthefield NICMOSF190N(black),andSpitzerIRAC(black)inthemid-IR.The
modelisreddenedwithanextinctionofE =8.3mag.
B−V
No. A E d logL MK lum.
Ks B−V
[mag] [mag] [kpc] [L ] type class
(cid:12)
#1 2.9 8.4 8.0 2.8 M0 II
5.3. WR102cstarcluster
#2 2.2 6.3 5.8 2.1 M1 III
#3 2.1 6.0 5.5 1.7 K1 III Thepresenceofearly-typestarswithin0.9pcofWR102cmay
#4 2.1 6.0 5.5 1.5 K4 III indicatethattheseobjectsrepresentanindependentcluster.Al-
#5 3.3 9.5 8.1 2.7 M0 II ternatively,theWR102cclustermayberelatedtothesamestar-
#6 2.9 8.3 8.0 2.7 M0 II burstthatproducedtheQuintupletCluster.Yetanotherpossibil-
#7 2.9 8.3 8.0 2.2 K5 III ityisthatalltheearly-typestarsclosetoWR102carepartofthe
#8 2.8 8.0 8.0 2.3 K4 II Quintuplet’stidaltail.SuchtailshavebeenpredictedbyHabibi
#9 1.9 5.6 5.3 1.8 M0 III et al. (2014) for the Arches and Quintuplet with extensions up
#10 2.9 8.3 8.0 3.6 M5-6 I to 1.6pc from the cluster centre. In any case, the presence of a
#11 2.9 8.2 8.0 2.6 K5 II cluster around WR102c seems to be inconsistent with the sce-
#12 2.8 8.0 8.0 3.0 M1 II nariothatWR102cwasbornintheQuintupletandejectedfrom
#16 2.6 7.5 7.3 3.1 K0 II there.
#18 2.8 8.0 8.0 2.3 K3 III We used the publicly available cluster evolution code
#19 2.2 6.3 5.8 1.9 K5 III McLuster (Küpper et al. 2011) to estimate the mass of the
#20 2.0 5.7 6.2 1.5 K5 III WR102c cluster. Assuming a standard Kroupa IMF (Kroupa
#21 2.5 7.3 7.2 1.8 M0 III 2001),themassoftheWR102cclusteris∼ 1000M .Thesim-
(cid:12)
#22 2.5 7.3 7.2 2.1 M0 III ulationaccuratelyreproducesthemassofthemostmassivestar
#23 2.2 6.3 5.8 1.9 K4 III andthenumberofearly-typestarsweobserved.Giventhesen-
#24 2.2 6.3 5.8 1.9 K2 III sitivityofourobservations(K = 14−15mag)wewereableto
s
detectonlystarsearlierthanB1-2,i.e.withmassesabove10M .
(cid:12)
Adoptinganenclosedmassof∼1000M andacharacteris-
(cid:12)
The brightest star in the field (no. 10 in Table2 and Fig.2) tic cluster radius R ≈ 1pc we estimate the velocity dispersion
0
is an M5-6I red supergiant. It is similar to the other late-type withintheclusterstarstobeonlyafewkms−1 (followingequa-
stars; we obtained its spectrum and fitted the SED as shown in tion1 in Kroupa 2002). In summary, the number of early-type
Figure10. The extinction and luminosity suggest that the star stars,theirages,masses,andradialvelocitiesconsistentlyagree
most likely resides in the GC region. On the other hand, its ra- withtheseobjectsbeingthebrightestmembersofayetunknown
dialvelocity(−45kms−1)isatoddswiththeradialvelocitiesof starcluster.
Articlenumber,page9of10
A&Aproofs:manuscriptno.wr102c_arxiv
6. Summaryandconclusions Ekström,S.,Georgy,C.,Eggenberger,P.,etal.2012,A&A,537,A146
Figer,D.F.,Kim,S.S.,Morris,M.,etal.1999a,ApJ,525,750
UsingVLTSINFONIweobtainedintegralfieldobservationsof Figer,D.F.,McLean,I.S.,&Morris,M.1999b,ApJ,514,202
0.25 square arcmin area around WR102c located at ≈ 2.5pc Fitzpatrick,E.L.&Massa,D.2009,ApJ,699,1209
(projected distance) from the Quintuplet Cluster in the GC re- Flagey,N.,Noriega-Crespo,A.,Billot,N.,&Carey,S.J.2011,ApJ,741,4
Freyer,T.,Hensler,G.,&Yorke,H.W.2006,ApJ,638,262
gion.
Garcia-Segura,G.&MacLow,M.-M.1995,ApJ,455,160
We identified five early-type stars (including WR102c) in
González-Fernández,C.,Cabrera-Lavers,A.,Hammersley,P.L.,&Garzón,F.
thisfield.Basedontheirage,radialvelocity,andmassdistribu- 2008,A&A,479,131
tion we suggest that these are the most massive members of a Gräfener,G.,Koesterke,L.,&Hamann,W.-R.2002,A&A,387,244
bound WR102c cluster with M ∼ 1000M . The existence of Gräfener,G.,Vink,J.S.,Harries,T.J.,&Langer,N.2012,A&A,547,A83
cl (cid:12) Gustafsson,B.,Edvardsson,B.,Eriksson,K.,etal.2008,A&A,486,951
suchaclusterquestionstheejectionscenarioforthepresentday
Gvaramadze,V.V.,Chené,A.-N.,Kniazev,A.Y.,etal.2014,MNRAS,442,929
locationofWR102c. Gvaramadze,V.V.,Fabrika,S.,Hamann,W.-R.,etal.2009,MNRAS,400,524
The detailed analysis of the stellar spectrum and photome- Habibi,M.,Stolte,A.,&Harfst,S.2014,A&A,566,A6
tryofWR102cbymeansofnon-LTEstellaratmospherePoWR Hainich,R.,Rühling,U.,Todt,H.,etal.2014,A&A,565,A27
Hamann,W.-R.&Gräfener,G.2004,A&A,427,697
models yielded stellar and wind parameters typical for a WN6
Hamann,W.-R.,Gräfener,G.,&Liermann,A.2006,A&A,457,1015
star(Table3).Theuncertaintyofthededucedstellarparameters
Hamann,W.-R.&Koesterke,L.1998a,A&A,335,1003
ofWR102cismildandmightreflectsomedeparturesofstellar Hamann,W.-R.&Koesterke,L.1998b,A&A,333,251
wind from spherical symmetry, e.g. due to the fast rotation or Hanson,M.M.,Conti,P.S.,&Rieke,M.J.1996,ApJS,107,281
binarity. Hanson,M.M.,Kudritzki,R.-P.,Kenworthy,M.A.,Puls,J.,&Tokunaga,A.T.
We produced a map of diffuse Brγ emission in the region 2005,ApJS,161,154
Homeier,N.L.,Blum,R.D.,Pasquali,A.,Conti,P.S.,&Damineli,A.2003,
aroundWR102c.Ourdataclearlyshowabipolarorring-shaped A&A,408,153
nebulacentredonWR102c.Thesamenebulaisclearlyseenin Houck,J.R.,Roellig,T.L.,vanCleve,J.,etal.2004,ApJS,154,18
theimagesfromtheHSTPaschen-αsurveyoftheGC.Accord- Ignace,R.,Oskinova,L.M.,&Foullon,C.2000,MNRAS,318,214
Kroupa,P.2001,MNRAS,322,231
ingtothespectraofthenebula,theprojectedexpansionvelocity
Kroupa,P.2002,MNRAS,330,707
is small. We suggest that the WR102c nebula is a typical WR
Küpper,A.H.W.,Maschberger,T.,Kroupa,P.,&Baumgardt,H.2011,MNRAS,
nebula formed recently as the result of the interaction of winds 417,2300
atdifferentevolutionarystages. Lang,C.C.,Goss,W.M.,&Wood,O.S.1997,ApJ,474,275
Lau,R.M.,Hankins,M.J.,Herter,T.L.,etal.2015,ArXive-prints
Law,C.&Yusef-Zadeh,F.2004,ApJ,611,858
Acknowledgments Liermann,A.,Hamann,W.,&Oskinova,L.M.2009,A&A,494,1137
Liermann,A.,Hamann,W.-R.,&Oskinova,L.M.2012,A&A,540,A14
This work has extensively used the NASA/IPAC Infrared Sci- Liermann,A.,Hamann,W.-R.,&Oskinova,L.M.2014,A&A,563,C2
Liermann,A.,Hamann,W.-R.,Oskinova,L.M.,Todt,H.,&Butler,K.2010,
ence Archive, the NASA Astrophysics Data System, and the
A&A,524,A82
SIMBAD database, operated at CDS, Strasbourg, France. This
Lucas,P.W.,Hoare,M.G.,Longmore,A.,etal.2008,MNRAS,391,136
publication makes use of data products from the Two Micron Marston,A.P.,Welzmiller,J.,Bransford,M.A.,Black,J.H.,&Bergman,P.
All Sky Survey, which is a joint project of the University of 1999,ApJ,518,769
Massachusetts and the Infrared Processing and Analysis Cen- Mauerhan,J.C.,Cotera,A.,Dong,H.,etal.2010,ApJ,725,188
ter/California Institute of Technology, funded by the National Mauerhan,J.C.,VanDyk,S.D.,&Morris,P.W.2011,AJ,142,40
Moneti,A.,Stolovy,S.,Blommaert,J.A.D.L.,Figer,D.F.,&Najarro,F.2001,
Aeronautics and Space Administration and the National Sci- A&A,366,106
ence Foundation. Some of the data presented in this paper Oskinova,L.M.2005,MNRAS,361,679
wereretrievedfromtheMikulskiArchiveforSpaceTelescopes Oskinova,L.M.,Hamann,W.-R.,&Feldmeier,A.2007,A&A,476,1331
Oskinova,L.M.,Ignace,R.,Hamann,W.-R.,Pollock,A.M.T.,&Brown,J.C.
(MAST). STScI is operated by the Association of Universities
2003,A&A,402,755
for Research in Astronomy, Inc., under NASA contract NAS5-
Oskinova,L.M.,Steinke,M.,Hamann,W.-R.,etal.2013,MNRAS,436,3357
26555.SupportforMASTfornon-HSTdataisprovidedbythe Oskinova,L.M.,Todt,H.,Ignace,R.,etal.2011,MNRAS,416,1456
NASAOfficeofSpaceScienceviagrantNNX09AF08Gandby Ramírez,S.V.,Arendt,R.G.,Sellgren,K.,etal.2008,ApJS,175,147
othergrantsandcontracts.WearegratefultoDr.R.Lauforshar- Reid,M.J.1993,ARA&A,31,345
Sander,A.,Hamann,W.-R.,&Todt,H.2012,A&A,540,A144
ingwithusthepreprintofhispaper.Wethanktherefereeforthe
Sander,A.,Shenar,T.,Hainich,R.,etal.2015,A&A,577,A13
usefulcommentsandsuggestions.Fundingforthisresearchhas Schmutz,W.,Hamann,W.-R.,&Wessolowski,U.1989,A&A,210,236
beenprovidedbyDLRgrant50OR1302(LMO)andDFGgrant Schneider,F.R.N.,Izzard,R.G.,deMink,S.E.,etal.2014,ApJ,780,117
HA1455/26(AS). Schultheis,M.,Chen,B.Q.,Jiang,B.W.,etal.2014,A&A,566,A120
Schultheis,M.,Ganesh,S.,Simon,G.,etal.1999,A&A,349,L69
Shenar,T.,Hamann,W.-R.,&Todt,H.2014,A&A,562,A118
References Skrutskie,M.F.,Cutri,R.M.,Stiening,R.,etal.2006,AJ,131,1163
Stolte,A.,Hußmann,B.,Morris,M.R.,etal.2014,ApJ,789,115
Barniske,A.,Oskinova,L.M.,&Hamann,W.2008,A&A,486,971 Toalá,J.A.&Arthur,S.J.2011,ApJ,737,100
Blum,R.D.,Ramírez,S.V.,Sellgren,K.,&Olsen,K.2003,ApJ,597,323 Toalá,J.A.,Guerrero,M.A.,Ramos-Larios,G.,&Guzmán,V.2015,A&A,
Blum,R.D.,Sellgren,K.,&Depoy,D.L.1996,AJ,112,1988 578,A66
Bonnet,H.,Abuter,R.,Baker,A.,etal.2004,TheMessenger,117,17 Todt,H.,Sander,A.,Hainich,R.,etal.2015,A&A,579,A75
Burgemeister,S.,Gvaramadze,V.V.,Stringfellow,G.S.,etal.2013,MNRAS, Tuthill,P.,Monnier,J.,Tanner,A.,etal.2006,Science,313,935
429,3305 vanDokkum,P.G.2001,PASP,113,1420
Cardelli,J.A.,Clayton,G.C.,&Mathis,J.S.1989,ApJ,345,245 vanMarle,A.J.,Langer,N.,&García-Segura,G.2007,A&A,469,941
Churchwell,E.,Babler,B.L.,Meade,M.R.,etal.2009,PASP,121,213
Vanbeveren,D.,VanBever,J.,&Belkus,H.2007,ApJ,662,L107
Cotera,A.S.,Simpson,J.P.,Erickson,E.F.,etal.1999,ApJ,510,747
Vink,J.S.,Gräfener,G.,&Harries,T.J.2011,A&A,536,L10
Dong,H.,Mauerhan,J.,Morris,M.R.,Wang,Q.D.,&Cotera,A.2015,MN-
Wachter,S.,Mauerhan,J.C.,VanDyk,S.D.,etal.2010,AJ,139,2330
RAS,446,842
Dong,H.,Wang,Q.D.,Cotera,A.,etal.2011,MNRAS,417,114 Wang,Q.D.,Dong,H.,Cotera,A.,etal.2010,MNRAS,402,895
Eisenhauer,F.,Abuter,R.,Bickert,K.,etal.2003,inSocietyofPhoto-Optical Wang,Q.D.,Dong,H.,&Lang,C.2006,MNRAS,371,38
Instrumentation Engineers (SPIE) Conference Series, Vol. 4841, Society
of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, ed.
M.Iye&A.F.M.Moorwood,1548–1561
Articlenumber,page10of10