Studies of a possible new Herbig Ae/Be star in the open cluster NGC 7380

1.1 MB·English

by  Blesson Mathew

ResearchinAstron.Astrophys.2012Vol.12No.2,167–176 R
esearchin
http://www.raa-journal.org http://www.iop.org/journals/raa A
stronomyand
A
strophysics
Studies of a possible new Herbig Ae/Be star in the open cluster
NGC 7380
2
1
0 BlessonMathew1,D.P.K.Banerjee1,N.M.Ashok1,AnnapurniSubramaniam2,B.
2 Bhavya2,3 andVishalJoshi1

n
a 1 AstronomyandAstrophysicsDivision,PhysicalResearchLaboratory,Navrangapura,Ahmedabad-
J 380009,Gujarat,India;[email protected]
4 2 IndianInstituteofAstrophysics,Bangalore-560034,India
2 3 CochinUniversityofScienceandTechnology,Cochin,India

]
R
Abstract We present a study of the star 2MASS J22472238+5801214 with the aim
S
of identifying its true nature which has hitherto been uncertain. This object, which is a
.
h member of the young cluster NGC 7380, has been variously proposed to be a Be star,
p a D-type symbiotic and a Herbig Ae/Be star in separate studies. Here we present opti-
-
o calspectroscopy,near-IRphotometryandnarrowbandHαimagingofthenebulosityin
r its environment.Analysis of all these results, including the spectral energy distribution
t
s constructedfrom available data, stronglyindicate the source to be a HerbigAe/Be star.
a Thestarisfoundtobeaccompaniedbyanebulositywithaninterestingstructure.Abow
[
shockshapedstructure,similartoacometarynebula,isseenveryclosetothestarwithits

1 apexorientedtowardsthephotoionizingsourceofthisregion(i.e.thestarDHCep).An
v interesting spectroscopicfinding,from the forbidden[SII] 6716,6731A˚ and [OI] 6300
6 A˚ lines,isthedetectionofablue-shiftedhighvelocityoutflow(200±50kms−1)from
5
thestar.
9
4
Keywords: stars:emission-line,Be–Stars:pre-mainsequence–stars:winds,outflows
.
1
–galaxies:starclusters:individual:NGC7380
0
2
1
1 INTRODUCTION
:
v
i 2MASS J22472238+5801214was identified as a Be star (category 4B) in the Hα emission-line star
X
survey by Kohoutek & Wehmeyer (1997) who found strong Hα emission in the spectra superposed
r
on a moderate continuum. On the other hand Corradi et al. (2008) identified this candidate as a D-
a
type symbioticbinaryfromthe IPHASHα emission-linesurvey.Thisclassification was based on the
observednear-IRandHαexcess,fromthelocationin(r−i)vs(r–Hα)and(J−H)vs(H−Ks)color-
colordiagrams.Symbioticsystemsareinteractingbinarieswithawhitedwarf(WD),acoolgiantand
anemittingnebula,createdbythephotoionizingfluxfromtheWDandcollisionofthewinds(Angeloni
etal.2007).SymbioticD-typecandidatesareseparatedfromS-typecandidatesbasedonthecontinuum
excess in 1–4 µm spectral region(Webster & Allen 1975).If the companionbelongsto an F/G giant
classratherthanaMiravariableone,thesystemisdesignatedasD’type(Allen1982).Thespectraof
symbioticbinariesarecharacterizedbythepresenceofhighionizationlinesandRamanscatteredOVI
emissionlinesinadditiontolowionizationmetallicabsorptionlinesandmolecularbands.
ApartfromtheBeclassificationofKohoutek&Wehmeyer(1997)andtheD-typesymbioticclas-
sificationofCorradietal.(2008),thepossibilityofthisobjectbelongingtotheHerbigAe/Be(HAeBe)
categorywasalsosuggestedbyMathewetal.(2008).Thisstarwasdetectedinemissionintheyoung
2 B.Mathewetal.
Table1 JournalofObservations
Object DateofObservation ModeofObs. Specifics
NGC7380(4) 2010-12-05 Hαimaging exp.60s,field10′×10′,HFOSC,2.0mHCT
2010-12-05 Hαimaging exp.40s,field2′×2′,HFOSC,2.0mHCT
2010-10-05 Spectroscopy Grism7/167l,exp.1200s,HFOSC,2.0mHCT
2010-10-05 Spectroscopy Grism8/167l,exp.1200s,HFOSC,2.0mHCT
2010-10-21 JHKphotometry NICMOS3,1.2mMtAbu
Nebulosity 2010-12-05 Spectroscopy Grism8/167l,exp.2400s,HFOSC,2.0mHCT
clusterNGC7380duringthesurveyofemission-linestarsinyoungopenclustersandcatalogedasNGC
7380(4).
Inallforthcomingtextweusethedesignation2MASSJ22472238+5801214orNGC7380(4)equiv-
alently.The object’s classification as HAeBe was discussed by Mathew et al.(2010)based on the fol-
lowingcharacteristics. Theobjectshowednear-IRexcessof ∼1mag in extinctioncorrected(J −H)
versus(H −K)color-colordiagram.Thestarwasalsofoundtobelocatedinthepositionoccupiedby
HAeBestarsintheHαequivalentwidth(EW)versus(H −K)diagram,whichisconventionallyused
toseparateClassicalBe(CBe)andHAeBestars.
It is thus seen that there is some uncertaintyaboutthe true nature of the objectwhich shouldde-
sirablyberesolved.We attempttodothisbyundertakinganin-depthanalysisoftheobjectproper,as
also its environment,by using photo-spectroscopicand imaging data. We believe that we are able to
makeasecureclassificationoftheobject’snatureinthepresentwork.Inadditionitisalsoshownthat
thesourceisfairlyinteresting,byvirtueofbeingassociatedwithahighvelocityoutflow,andworthyof
furtherstudies.
A few wordson the physicalenvironmentof the targetobjectin the presentstudy maybe appro-
priate.Masseyetal.(1995)identifiedthisstarasamemberoftheyoungopencluster(∼2Myr)NGC
7380(starno:2249)withvisualmagnitudemV =14.72,colorexcessE(B−V)=0.64anddistance3.6
kpc.Thestarislocatedawayfromtheclustercenterandassociatedwithpre-mainsequencestars.The
starislessthan0.25Myrfromapre-mainsequence(PMS)isochronefittingintheV versus(B −V)
colormagnitudediagram(Mathewetal.2010).ThetargetNGC7380(4)isassociatedwitharelatively
large(θ =25’)andevolvedHII regionSharpless142(S142;Roy&Joncas1985).Themainsourceof
ionizationisanO6spectroscopicbinaryDHCep,whichisalsoamemberoftheclusterNGC7380.The
regionis quitecomplex,showingassociationwith an HI cloudand molecularcloudNGC7380E(see
fig.1inChavarria-K.etal.1994).
2 OBSERVATIONS
The spectroscopic observations were done using the HFOSC (Himalayan Faint Object Spectrograph
Camera)availablewiththe2.0mHimalayanChandraTelescope(HCT),operatedbytheIndianInstitute
ofAstrophysics,India.TheCCDusedforimagingwasa2K×4KCCD,wherethecentral500×3500
pixelswereusedforspectroscopy.Thepixelsizewas15µmwithanimagescaleof0.297arcsec/pixel.
ThespectraweretakenusingaGrism7(3800–6800A˚)and167µmslitcombinationintheblueregion
whichgaveaneffectiveresolutionof10A˚ neartheHβ line. Thespectra intheredregionweretaken
usingaGrism8(5500–9000A˚)and167µmslitsetup,whichgaveaneffectiveresolutionof7A˚ nearthe
Hαline.Thespectrawerefoundtohavegoodsignaltonoiseratio(≥100).TheHFOSCwasalsoused
inimagingmodetoobtainabroadband(6300–6740A˚)Hαimageofthesourceanditsenvironment.
JHK photometric observations of the object were made from Mt. Abu Infrared Observatory on
2010 October 21 using the 256×256 NICMOS3 imager-spectrograph.The procedure for the near-IR
photometricobservationsandthesubsequentreductionandanalysisofdatafollowedastandardproce-
duredescribede.ginBanerjee&Ashok(2002).Allspectroscopicandphotometricdatawerereduced
andanalyzedusingIRAFtasks.AconsolidatedlogoftheobservationsisgiveninTable1.
HerbigAe/BeStarinNGC7380 3
10’’
DH Cep
2
1
Fig.1 Leftpanelshowsa10′ ×10′ fieldaroundtheobjectofinterestobtainedwithanHα
broad band filter. NGC 7380(4) and DH Cep are shown surroundedby a circle and square
respectively.Therightpanelshowsazoomedimage(2′×2′)ofthenebulosityaroundNGC
7380(4). In both panels, north is to the top and east to the left. More details are given in
Section3.1.
3 RESULTS
3.1 HαImaging:ANebulosityAroundtheObject
TheHαimageoftheregionandanenlargedsectionaroundthestarareshownintheleftandrightpanels
ofFigure1respectively.Anebulosityisclearlyseenaroundtheobjectwhoseprincipalfeaturesconsist
ofadiffusepatch(feature2)andabow-shockshapedstructure(feature1)veryclosetothestar.Thebow
shaped structure looks like a cometaryglobule (cometary nebula) with the apex, as expectedin these
objects,orientedtowardsthe photoionizingsourcewhichin thisparticularcase isDH Cep. Cometary
globulesarepotentialsitesofinducedstarformationduetocompressionbyionizationorshockfronts,
createdbytheinfluxofUV radiationfromthemassiveexcitingstar. Ikedaetal.(2008)foundsix Hα
emissionstarsnearthetipofthecometaryglobuleBRC37,whichareformedduetothesequentialstar
formationtriggeredbyO-typestarsHD206267andHD206183.Sugitanietal.(1991)catalogedforty
fourbrightrimmedcloudswithIRASpointsources,whicharepossiblecandidatesforstarformationby
radiation-drivenimplosion.OurcandidatewasnotlistedinthecatalogeventhoughS142wasidentified,
whichisseenasabrightrimtotheleftoftheobjectinthe10′×10′field(Fig.1).
Negueruelaet al. (2007)studied triggeredstar formationin NGC 1893,which is similar to NGC
7380intermsofageandstarformationactivity.FromHαimagingandslitlessspectroscopytheyiden-
tified a Herbig Be star S1R2N35 in the immediate vicinity of cometary nebula Sim 130 (a striking
imageofthiscometarynebulaisshownintheabovework).Alsoonecanseebowshapedstructureand
nebulosityassociatedwiththisregionwhicharetriggeredbynearbymassivestars.Thisshowsthatthe
presenceofa HerbigBe starin thevicinityofa cometaryglobuleispossibleandsupportsanHAeBe
classificationforNGC7380(4).
3.2 SpectroscopyoftheSource
TheopticalspectrumofNGC7380(4)ispresentedin Figure2.Allthelinesareseen inemissionand
absorptionfeatures,ifany,arenotprominent.HydrogenlinesoftheBalmerandPaschenseriesareall
4 B.Mathewetal.
3
2.5
2
1.5
1
4000 4500 5000 5500
2
1.5
1
5500 6000 6500 7000
2
1.5
1
7000 7500 8000 8500 9000
Fig.2 Optical spectrum of NGC 7380 between 4000–9000 A˚ taken on 2010-10-05. The
prominentlinesareidentified.
inemission;itmaybenotedthatthehigherorderlinesoftheseseriesareusuallyseeninabsorptionin
thespectrumofBestars.TheHαlineisthemostintense(EW∼−100A˚)inthespectrumwithbroad
wingsextendingfrom6530to6595A˚.TheotherprominentlinesseenareduetoCaII,neutrallinesof
NaI andKI, permittedandforbiddenlinesofOI, [SII],a fewlinesofHeI andalargenumberoflines
fromFeII. Line identificationis largelybasedon thedetailed listof linestypicallyseenin the spectra
ofHAeBestarspresentedinHerna´ndezetal.(2004).SeveralweakfeaturesinthespectrumofFigure2
remainunidentified.Comparisonoftheirwavelengthswithatomiclinelistssuggeststhatmanyofthem
couldbeduetoFeI.However,asecureidentificationisdifficulttoarriveatandforthepresentstudywe
leavethemasunidentified.
HerbigAe/BeStarinNGC7380 5
1.4
[O I](6300.3) [O I](6363.8) Fe II(6433) Fe II(6516)
Fe II(6456)
1.2
1
6300 6350 6400 6450 6500
1.2
[S II](6716.4)
1.15 [S II](6730.8)
He I(6678)
1.1
1.05
1
0.95
6600 6650 6700 6750 6800 6850
Fig.3 [OI]λλ6300,6364and[SII]λλ6716,6731lineprofilesobservedintheobject.
Table2presentstheprominentlinesseeninthespectraalongwiththeequivalentwidthswhichhave
typicalmeasurementerrorsofaround5to10%.Inthecasewherelineswereblended,weemployeda
deblendingprocedureinvolvingthefittingofmultiplegaussianstotheobservedprofile.Theequivalent
widthsoftheindividualgaussianswerethenestimated.Lineswithuncertainidentificationaremarked
withaquestionmarkinthefirstcolumnofTable2.
Aninterestingaspectofthespectraistheevidenceofafastoutflowasinferredfromthebehaviorof
theforbiddenlinesof[SII]λλ6716/6731and[OI]λλ6300/6364.Thepresenceoftheseforbiddenlinesin
thespectraofHAeBestars,andintheirlowermasscounterparts-theclassicalTTauristars(CTTS),has
longbeenusedtoinferthepresenceofjets/outflowssincesuchlinesariseonlyinlowdensityconditions
andhencearetracersoflowdensitymaterial(Finkenzeller1985,Corcoran&Ray1998,Appenzelleret
al.1984).
Figure3showsamagnifiedsectionofthespectraaroundtheforbiddenlinesshowingtheselinesto
beblueshiftedby∼4to5A˚ whereasotherlinesinthespectrumareseenattheirexpectedwavelengths.
The measured mean blue-shiftfor the [SII]λλ6716/6731lines is 215 ± 50 km s−1 while that for the
[OI]λ6300lineis176±50kms−1.Thusthereisevidenceforthepresenceofahighvelocityoutflow
emanatingfromthestar.Theratiooftheemissionstrengthsofthe[SII]doublet(6716/6731)isaround
0.42 indicating that the electron density is close to (or greater than) ∼ 104 cm−3 if a temperature of
10000Kisassumed(Osterbrock&Ferland2006,Cantoetal.1980).Suchavalueoftheelectrondensity
isslightlyonthehighersidecomparedtoHIIornebularregions;butsimilarvalueshavebeenobserved
incertainpartsofasimilar[SII]outflowemanatingfromtheHAeBestarLkHα233(Corcoran&Ray
1998). It may be noted that the absorption feature seen to the left of the [OI]λ6300 line, giving it an
apparentP-Cygnistructure,isactuallyaDiffuseInterstellarBand.
TheCaIItriplet(8498A˚,8542A˚,8662A˚)linesareblendedwiththePaschenlinesPa16,Pa15and
Pa13respectively.ThecontributionofthesePaschenlinesisestimatedbyinterpolatingthestrengthsof
theisolatedadjacentPaschenlinesPa17,Pa14andPa12andremovedfromtheCaIItripletlinestrengths.
Fromthesecorrectedequivalentwidthvalues,therelativestrengthoftripletlinesarefoundtobeinthe
ratio1.0:0.98:0.84.Thisisvastlydifferentfromtheexpectedstrengthsof1:9:5,whichistheratioof
6 B.Mathewetal.
1
0.8
0.6
0.4
0.2
0
6400 6500 6600 6700 6800
Fig.4 Spectrumofthe nebulosityfeature2 markedin Fig. 1. Theprominentlinesseen are
[NII]λλ6548,6583;Hαand[SII]λλ6716,6731.HeIλ6678isalsoweaklyseen
theirrespectivegfvalues.ThisimpliesthattheCatripletlinesaresubjecttolargeopticaldeptheffects.
Itmaybenotedthattheintensityofthe8498A˚ lineisgreaterthanthe8542A˚ line,whichisaunique
characteristicofPMSstars(Hamann&Persson1992).
Could NGC 7380(4) be a symbiotic star? Based on the examples of well-studied and widely ac-
ceptedsymbioticobjectsBelczyn´skietal.(2000)adoptedthefollowingspectralcriteriatoclassifyan
objectasasymbioticstar:(i)thepresenceofabsorptionfeaturesofalate-typegiantlikeTiO,H2O,CO,
CN,orVObandsaswellasCaI,CaII,FeI,orNaIabsorptionlines(ii)thepresenceofstrongemission
lines of HI and HeI and either emission lines of ions with ionization potential of at least 35 eV like
[OIII]orhighionizationlinesfrom[FeVII]λλ5721,6086,HeIIλλ4686,5411andCaVλ6086(Corradi
& Giammanco 2010) (iii) the presence of Raman scattered 6825 A˚ emission feature. Schmid (1989)
identifiedRamanscatteredOVI lines(6825A˚ and7082A˚)inthespectraofsymbioticbinaries,which
are not observed in other astrophysicalobjects. These lines are producedby Raman scattering of the
OVIλλ1032/1038resonancelinesbyneutralhydrogen.Sincenoneofthesecriteriaaremetinthecase
ofNGC7380(4)itisunlikelytobeasymbioticstar.Further,theattributedassociationofthestarwitha
youngclusterwhoseageis2Myrindicatesittobeayoungobject;symbioticstarsarerelativelymore
evolvedsystemsasimpliedbythepresenceofaWDasoneofthecomponents.
Aspectrum(5500–9000A˚)ofthenebulosity(feature2inFig.1)wastakenwiththeslitpositioned
along NS (PA = 0o) and an exposure time of 2400 s. The spectrum is typically nebular with a weak
continuum,whichbarelyregistersabovethedarkcountsofthedetector,withtheprominentlinesbeing
[NII]λλ6548/6583, Hα and [SII]λλ6716/6731. This part of the spectrum is shown in Figure 4. Very
few additional lines are seen and these are HeIλλ5876, 6678, [OI]λ6300 and an unidentified line at
7136A˚ (possibly[ArII]).Itispossiblethatthisnebulositycouldbepartiallyareflectionnebulosityand
partially an ionized region. The observed [SII] (6716/6731) ratio of 1.16 in the nebulosity implies a
electrondensityintherange∼100–150cm−3 assumingatemperatureof10000K.Itisdifficulttobe
certain whether the region is shock ionized or photo-ionizedby the UV flux from DH Cep. In shock
ionization, low-ionization lines like [SII]λλ6716/6731 are much stronger with respect to Hα than in
HerbigAe/BeStarinNGC7380 7
Table2 EmissionlinesinNGC7380(4)
Element λ EW Element λ EW Element λ EW
(A˚ ) (A˚ ) (A˚ ) (A˚ ) (A˚ ) (A˚ )
CaIIK 3933 −19.1 Hβ 4861 −18.3 Hα 6563 −100.1
CaII/HI 3970 −6.5 FeII(42) 4924 −3.6 HeI 6678 −0.7
FeI? 4063 −4.1 FeII(42) 5018 −3.1 [SII] 6716 −0.6
Hδ 4101 −5.4 FeII(42) 5169 −5.6 [SII] 6731 −1.4
FeI? 4130 −3.2 FeII(49) 5198 −3.9 HeI 7065 −0.4
FeII(27,28) 4176 −5.5 FeII(49) 5235 −2.8 FeII 7712 −1.0
FeII(27) 4233 −1.8 FeII(49) 5276 −5.4 OI 7772 −2.1
TiII(41) 4313 −1.2 FeII(48,49) 5317 −4.2 Pa21 8374 −0.8
Hγ 4340 −6.6 FeII(49) 5326 −1.5 Pa20/FeI 8387 −2.2
FeII(27) 4352 −3.9 FeII(48) 5338 −2.4 Pa19 8413 −0.9
HeI+FeII(27) 4385 −1.2 FeII(48) 5363 −1.7 OI 8446 −9.7
TiII(19) 4395 −0.9 FeII(55) 5535 −0.6 Pa17 8467 −2.4
FeII(27) 4417 −1.8 HeI 5876 −1.6 CaII 8498 −34.3
HeI 4471 −1.9 NaI 5890/96 −0.9 CaII 8542 −33.5
FeII(37) 4491 −1.9 FeII(74) 6149 −0.9 Pa14 8598 −2.1
FeI/FeII? 4519 −2.6 FeII(74) 6238 −0.5 CaII 8662 −29.0
FeII(38) 4549 −3.5 FeII(74) 6248 −1.3 FeI 8688 −2.0
FeII(37,38) 4584 −2.6 [OI] 6300 −3.3 Pa12 8750 −3.3
FeII(38) 4621 −2.6 FeII(40) 6433 −1.4 MgI 8806 −1.1
FeII(37) 4629 −3.6 FeII(74) 6456 −1.4 FeI 8824 −1.0
FeI(37) 4667 −1.0 FeII(40) 6516 −1.9 Pa11 8862 −4.1
typicalphotoionizedHIIregions(Osterbrock&Ferland2006;Hartiganetal.1994;theHαtoSII[6717
+6731]ratiocanbearoundunity).Forarepresentativecomparison,Osterbrock&Ferland(2006)listed
lineintensitiesintheOrionnebula(photoionized)andashockionizedfilamentinCasA.Theobserved
I(Hα)/I(6716)ratioisabout90intheformerand2.6inthelatter.InourcaseI(Hα)/I(6716)hasavalue
of∼6.4,closertothatexpectedinashock-ionizedregion.Thusapartofthe[SII]emissionseeninthe
nebulositymayarisefromashock.However,adeeperstudyofthisregionisdesirable,todrawfirmer
conclusions.
3.3 SpectralEnergyDistribution
The photometric data spanning the optical to mid-infrared spectral region are presented in Table 3.
Thesedataareusedtoconstructthespectralenergydistribution(SED),whichisshowninFigure5.It
shouldbenotedthattheoptical,near-IRandmid-IRobservationsaredoneatdifferentepochs.Thetwo
setsofnear-IRmeasurementsseparatedbytenyearsdonotshownoticeablevariability.Thereddening
correctionsweredoneusingrelationsfromRieke&Lebofsky(1985)withE(B−V)=0.64(Masseyet
al.1995).TheSEDshowsaclearIRexcessandtheIRluminosityissignificantlylargerthantheoptical
luminosity.ThisisatypicalcharacteristicofHAeBestarsbelongingtotheGroupIIclass(Hillenbrand
etal.1992).TheSEDofGroupIIobjectsisinterpretedintermsofasphericalenvelopeandregardedas
theprecursorstoHAeBestarswithacircumstellardisk.Wehavefittedmultipleblackbodiestoidentify
differentcomponentsintheSED.Themultipleblackbodyfitsuggeststhepresenceofahotcomponent
withatemperatureof∼9100Kandtwoadditionalcomponentslikelytobeassociatedwithdust,with
temperatureof∼2100Kand∼300Krespectively.However,theuseofanappropriateradiative-transfer
codelikeDUSTYisnecessary,whichisbeyondthescopeofthispaper,toproperlyestimatethephysical
parametersofthedustenvelopesurroundingthecentralstar.
3.4 HAeBeNatureoftheCandidate
Herbig(1960)classifiedHAeBestarsonthebasisofthefollowingcriteria:(a)thespectraltypeisAor
earlier,with emissionlines, (b)the star liesin anobscuredregion,and(c)the starilluminatesa fairly
brightnebulosityinitsimmediatevicinity.Waters&Waelkens(1998)modifiedtheabovedefinitionand
8 B.Mathewetal.
Fig.5 SpectralenergydistributionofthesourceisshownusingthedatainTable3.BVRI
pointsareshowninsquares,JHKs in triangles,MSX indiamonds,AKARI incrossesand
IRASin‘+’symbols.Blackbodyfitsattemperaturesof9100K(dottedline),2100K(dashed
line)and300K(dot-dashedline)areshownalongwiththeirco-addedsumwhichisshown
byasolidline.
Table3 AvailableOptical-IRPhotometricMeasurements
Source Wavelength/band Flux/mag
NOMAD B 15.69
Masseyetal.(1995) V 14.72
IPHAS R 14.00
Hα 12.85
I 12.95
2MASS(Mt.Abu) J 10.80(10.88)
H 9.76(9.71)
Ks 8.85(8.75)
MSX6C 8.28µm 0.73Jy
14.65µm 1.29Jy
IRAS 12µm 0.96Jy
25µm 1.77Jy
AKARI 18µm 1.40Jy
removedtheconstraintofanassociatednebulositybyconsideringthefactthatisolatedHAeBestarsare
also seen, whichwereidentifiedfromtheIRAS far-IRall skysurvey.Hence theyproposethepresent
working definition of HAeBe stars as: (a) spectral type A or B with emission lines, (b) infrared (IR)
excessduetohotorcoolcircumstellardustorboth,and(c)luminosityclassIIItoV.Inthefollowing
discussionwehaveanalyzedthemeritsofNGC7380(4)asanHAeBecandidate.
As explained in Section 3.2, the spectra of NGC 7380(4)show emission lines. The estimation of
spectraltypefromspectroscopyisnotpossiblesinceabsorptionlinesofhydrogenandheliumareabsent.
Thus, if the spectral class is to be identified even in a very broad sense, we have to take recourse to
photometricdata.Using severalstarsin thecluster,Masseyetal. (1995)estimatedthedistance ofthe
cluster to be 3732pc and also estimated a mean reddeningto be E(B −V) = 0.64.Using this value
ofthereddeningandanapparentmagnitudemV =14.72fortheobject,anabsolutemagnitudeofMV
= −0.12 was derived. This would correspond to a B8 – B9 spectral type if it is of luminosity class
HerbigAe/BeStarinNGC7380 9
V and B9 – A0 if it is of luminosity class III (Schmid-Kaler 1982). However, there is likely to be a
variationintheintra-clusterreddeningasshownbyMasseyetal.(1995)whosesampleofstarsshowed
avariationinE(B −V)between0.52to0.86.Therefore,usingthemeanvalueofE(B −V)=0.64
couldleadtoerrorsinestimatingtheabsolutemagnitudeandhencethespectraltypeofthestar.Thus,
thephotometricdatabroadlysuggestthatNGC7380(4)isalateBorearlyAtypestar,whichisinline
withtherequirementforittobeanHAeBestar.FromitsSEDweidentifiedIRexcessinthisstar,which
isconsideredasadefiningpropertyofHAeBestars.Thestarisalsoassociatedwithanebulositywhose
presencefurtherstrengthenstheHAeBeclassificationoftheobject.Thespectroscopicsupportforsuch
aclassificationhasalreadybeendiscussed.
4 SUMMARY
We have presented a study of the object NGC 7380(4) (equivalently 2MASS J22472238+5801214)
whose classification was hitherto uncertain. The star is shown to satisfy many of the characteristics
of HAeBe stars viz. a similar spectrum, association with a star forming region, an SED showing an
infra-red excess that is expected of this category of stars, the presence of a surrounding nebulosity
and a suggestedyoungage by virtueof beingassociated with the youngcluster NGC 7380.It is thus
stronglysuggestedthattheobjectisanHAeBestarratherthanaD-typesymbioticoraBestar.Wefind
spectroscopicevidence,based on the forbiddenlines of [SII] and [OI], for the interestingpresence of
a200±50kms−1 highvelocityoutfloworiginatingfromthestar.FromHαimaging,anebulosityis
clearlyseenaroundtheobjectwhoseprincipalfeaturesconsistofadiffusepatch(eastofthestar)anda
bow-shockshapedstructuretypicalofacometarynebula.Theapexofthiscometarynebulaisseento
pointtowardsthestarDHCepwhichisbelievedtobethehotphotoionizingsourceofthisregion.Such
an orientation of the cometary nebula towards the ionizing source is generally seen in other similar
objects.
Acknowledgements TheresearchworkatPhysicalResearchLaboratoryisfundedbytheDepartment
ofSpace,GovernmentofIndia.WewouldliketoacknowledgetheassistanceofPepsiAnto,thestaffin
HanleandthoseinMt.Abuduringtheobservations.
References
Allen,D.A.1982,inIAUColloq.70:TheNatureofSymbioticStars,Vol.95,eds.,M.Friedjung&R.Viotti,27
Angeloni,R.,Contini,M.,Ciroi,S.,Rafanelli,P.2007,A&A,472,497
Appenzeller,I.,Oestreicher,R.,Jankovics,I.1984,A&A,141,108
Banerjee,D.P.K.,Ashok,N.M.2002,A&A,395,161
Belczyn´skiK.,MikołajewskaJ.,MunariU.,Ivison,R.J.,FriedjungM.2000,A&AS,146,407
Canto,J.,Meaburn,J.,Theokas,A.C.,Elliott,K.H.1980,MNRAS,193,911
Chavarria-K.C.,Moreno-Corral,M.A.,Hernandez-Toledo,H.,Terranegra,L.,deLara,E.,1994,A&A,283,963
Corcoran,M.,Ray,T.P.1998,A&A,336,535
Corradi,R.L.M.,Giammanco,C.2010,520,A99
Corradi,R.L.M.,Rodr´ıguez-Flores,E.R.,Mampaso,A.etal.2008,A&A,480,409
Finkenzeller,U.1985,A&A,151,340
Hamann,F.,Persson,S.E.1992,ApJS,82,285
Hartigan,P.,Morse,J.A.,Raymond,J.1994,ApJ,436,125
Herbig,G.H.,1960,ApJS,4,337
Herna´ndez,J.,Calvet,N.,Bricen˜o,C.,Hartmann,L.,Berlind,P.2004,AJ,127,1682
Hillenbrand,L.A.,Strom,S.E.,Vrba,F.J.,Keene,J.1992,ApJ,397,613
Ikeda,H.,Sugitani,K.,Watanabe,M.,Fukuda,N.etal.2008,AJ,135,2323
10 B.Mathewetal.
Kohoutek, L., Wehmeyer, R., 1997, Catalogue of stars in the northern Milky Way having H-alpha in emission
(Hamburg:Sternwarte)
Massey,P.,Johnson,K.E.,Degioia-Eastwood,K.,1995,ApJ,454,151
Mathew,B.,Subramaniam,A.,Bhatt,B.C.2008,MNRAS,388,1879
Mathew,B.,Subramaniam,A.,Bhavya,B.2010,BulletinoftheAstronomicalSocietyofIndia,38,35
Negueruela,I.,Marco,A.,Israel,G.L.,Bernabeu,G.2007,A&A,471,485
Osterbrock, D. E., Ferland, G. J. 2006, Astrophysics of gaseous nebulae and active galactic nuclei (2nd
ed.:Sausalito,CA:UniversityScienceBooks)
Rieke,G.H.,Lebofsky,M.J.1985,ApJ,288,618
Roy,J.-R.,Joncas,G.1985,ApJ,288,142
Schmid,H.M.1989,A&A,211L,31S
Schmidt-Kaler, Th. 1982, Landolt-Bo¨rnstein: Numerical Data and Functional Relationships in Science and
Technology,ed.K.Schaifers,&H.H.Voigt(Berlin:Springer),VI/2b
Sugitani,K.,Fukui,Y.,Ogura,K.1991,ApJS,77,59
Waters,L.B.F.M.,Waelkens,C.1998,ARA&A,36,233
Webster,B.L.,Allen,D.A.1975,MNRAS,171,171
ThispaperwaspreparedwiththeRAALATEXmacrov1.2.