The VLT-FLAMES Survey of Massive Stars: Observations centered on the Magellanic Cloud clusters NGC 330, NGC 346, NGC 2004, and the N11 region

0.62 MB·English

by  C. J. Evans

Astronomy&Astrophysicsmanuscriptno.4988 February5,2008
(DOI:willbeinsertedbyhandlater)
The VLT-FLAMES Survey of Massive Stars: Observations
centered on the Magellanic Cloud clusters NGC330, NGC346,
⋆ ⋆⋆
NGC2004, and the N11 region
1 2 3 3
C.J.Evans ,D.J.Lennon ,S.J.Smartt ,andC.Trundle
7
0 1 UKAstronomyTechnologyCentre,RoyalObservatoryEdinburgh,BlackfordHill,Edinburgh,EH93HJ,UK
0 2 TheIsaacNewtonGroupofTelescopes,ApartadodeCorreos321,E-38700,SantaCruzdeLaPalma,CanaryIslands,Spain
2 3 DepartmentofPhysics&Astronomy,Queen’sUniversityBelfast,BelfastBT71NN,NorthernIreland,UK

n
a
J Abstract. Wepresent new observations of470 starsusing theFibreLargeArrayMulti-ElementSpectrograph (FLAMES)

5 instrumentinfieldscenteredontheclustersNGC330andNGC346intheSmallMagellanicCloud(SMC),andNGC2004and
theN11regionintheLargeMagellanicCloud(LMC).Afurther14starswereobservedintheN11andNGC330fieldsusing

2 theUltravioletandVisualEchelleSpectrograph(UVES)foraseparateprogramme.Spectralclassificationsandstellarradial
v velocitiesaregivenforeachtarget,withcarefulattentiontochecksforbinarity.Inparticular,wehaveinvestigatedpreviously
5 unexploredregionsaroundthecentralLH9/LH10complexofN11,finding∼25newO-typestarsfromourspectroscopy.We
0
haveobservedarelativelylargenumberofBe-typestarsthatdisplaypermittedFeIIemissionlines.Theseareprimarilynotin
4
theclustercoresandappeartobeassociatedwithclassicalBe-typestars,ratherthanpremain-sequenceobjects.Thepresence
6
0 of the Fe II emission, as compared to the equivalent width of Hα, is not obviously dependent on metallicity. We have also
explored therelativefractionof Be- tonormal B-typestarsinthefield-regionsnear toNGC330and NGC2004, findingno
6
0 strongevidenceofatrendwithmetallicitywhencomparedtoGalacticresults.Aconsequence ofserviceobservationsisthat
/ wehavereasonabletime-samplinginthreeofourFLAMESfields.WefindlowerlimitstothebinaryfractionofO-andearly
h
B-typestarsof23to36%.Oneofourtargets(NGC346-013) isespeciallyinterestingwithamassive,apparentlyhotter,less
p
luminoussecondarycomponent.
-
o
r
t
s Keywords.stars:early-type–stars:fundamentalparameters aparticularlylargedataset.Inparalleltothiscatalogue,subsets
a
–stars:emission-line,Be–binaries:spectroscopic–galaxies: ofthesamplearenowbeinganalysedbydifferentgroups.The
:
v MagellanicClouds sourcesofphotometryandastrometryusedfortargetselection
i
X aregiveninSection2,followedbydetailsoftheobservations
inSection 3,andthenadiscussionoftheobservedsample.
r
1. Introduction
a
Two FLAMES pointings were observed in each of the
As part of a European Southern Observatory (ESO) Large
Clouds, centered on NGC346 and NGC330 in the SMC,
Programmewehavecompletedanewspectroscopicsurveyof
and on NGC2004 and the N11 region (Henize 1956) in the
massive stars in fields centered on open clusters in the Large
LMC. NGC346 is a young cluster with an age in the range
and Small Magellanic Clouds (LMC and SMC respectively) of 1 to 3×106 yrs(Kudritzkietal. 1989;Walbornetal. 2000;
and the Galaxy. The survey has employed the Fibre Large
Bouretetal.2003;Masseyetal.2005),thathasclearlyunder-
Array Multi-Element Spectrograph (FLAMES) instrument at
gone prodigious star formation. It is also the largest H II re-
theVeryLargeTelescope(VLT),thatprovideshigh-resolution
gion in the SMC. The best source of spectroscopic informa-
(R ∼20,000) multi-object spectroscopy over a 25’ diameter tioninNGC346isthestudybyMasseyetal.(1989, hereafter
field-of-view. The scientific motivations for the survey, and
MPG),whofoundasmanyO-typestarsintheclusteraswere
the observational information for the three Galactic clusters
knownintherestoftheSMCatthattime.High-resolutionop-
(NGC3293, NGC4755, and NGC6611), were presented by
tical spectra of five of the O-type stars from MPG were pre-
Evansetal.(2005,hereafterPaperI).
sentedbyWalbornetal.(2000, togetherwith AzV220thatis
In this paperwe presentthe FLAMES observationsin the also withintheFLAMESfield-of-view).Thesewereanalysed
MagellanicClouds.Thematerialpresentedislargelyadiscus- byBouretetal.(2003),inconjunctionwithultravioletdata,to
sionofthespectralclassificationsandradialvelocitiesofeach derivephysicalparameters.
star,andprovidesaconsistentandthoroughoverviewofwhatis
N11isalsoarelativelyyoungregionandincludestheOB
Sendoffprintrequeststo:[email protected] associations LH9, LH10 and LH13 (Lucke&Hodge 1970),
2 C.J.Evansetal.:FLAMESSurveyofMassiveStars:LMC&SMCclusters
thatare of interestin the contextofsequentialstar-formation, 2. Targetselection
see Walborn&Parker (1992), Parkeretal. (1992, hereafter
2.1. SMC photometry
P92),andBarb´aetal. (2003).P92 illustrated howrich the re-
gionisintermsofmassivestars,presentingobservationsof43 The adopted photometry and astrometry for the targets in
O-typestarsinLH9andLH10,withthreeO3-typestarsfound NGC346 and NGC330 is that from the initial ESO Imaging
in LH10. These O3 stars were considered by Walbornetal. Survey(EIS)pre-FLAMESreleasebyMomanyetal.(2001).
(2002) in their extension of the MK classification scheme to
includethenewO2subtype,withoneofthestarsfromP92re-
2.2. N11photometry
classifiedasO2-type.TheFLAMESobservationsinN11pre-
sentedanopportunitytoobtaingood-qualityspectroscopyofa
The N11 region was not covered by the EIS pre-FLAMES
largenumberofknownO-typestars,whilstalsoexploringthe
Survey and so we obtained 60s B and V images with the
spectralcontentofthishighly-structuredanddynamicregion.
WideFieldImager(WFI)atthe2.2-mMaxPlanckGesellschaft
(MPG)/ESO telescope, on 2003 April 04. These were pro-
NGC330 and NGC2004 are older, more centrally con- cessed by Dr. M. Irwin using a modified version of the Isaac
densed clusters. NGC330 in particular has been the focus of Newton Telescope–Wide Field Camera (INT–WFC) data re-
much attention in recent years. Feast (1972) presented Hα ductionpipeline(Irwin&Lewis2001),wethencalibratedthe
spectroscopy of 18 stars in the cluster, and noted: ‘It is also photometrytothe Johnson-Cousinssystemusingresultsfrom
an object of considerable importance in discussion of possi- P92.
ble differences between stars of the same age in the SMC As in PaperI, for photometriccalibrationwe preferto vi-
and in the Galaxy’. The community has clearly taken his sually match stars using published finding charts. In crowded
words to heart – in the past 15 years there have been nu- regions such as those in our FLAMES fields this ensures ac-
merous studies in the cluster, most of which were concerned curatecross-identification.Cross-referencingthefindingcharts
with the large population of Be-type stars therein, namely of P92 with the WFI images yielded matches of 41 stars (for
Grebeletal.(1992),Lennonetal.(1993),Grebeletal.(1996), which both B and V WFI photometry were available), with
Mazzalietal. (1996), Keller&Bessell (1998), Kelleretal. relatively sparse sampling in terms of (B − V). To increase
(1999), Maederetal. (1999), and Lennonetal. (2003). The the number of cross-matched stars an astrometric search was
paper from these with the widest implications is that from performedbetweentheWFIsourcesandthefullP92catalogue
Maederetal. (1999), who compared the fraction of Be stars (availableon-lineat the Centre de Donn´ees astronomiquesde
(relative to all B-type stars) in a total of 21 clusters in the Strasbourg). The mean (absolute) offsets found between the
SMC,LMCandtheGalaxy.ThefractionofBestarsappearsto WFIandP92astrometry(forthe41starswithvisualmatches),
increase with decreasingmetallicity,althoughtheir study was were<|∆δ|>∼0.4′′and<|∆α|>∼0.06s;thesewereused
limitedtoonlyonecluster(NGC330)intheSMC.Thistrend to thenexpandthe sampleto 60stars, with V <17.0.TheV
led Maederetal. to advance the possibility of faster rotation andBcolourtermsfoundfortheWFIdatainN11areshownin
rates at lower metallicities – one of the key scientific motiva- Figures1and2,andthetransformationequationsfoundwere:
tionsthatpromptedthisFLAMESsurvey.
VJ =VWFI−0.07×(B−V)J−0.34, (1)
In contrast to NGC330, with the exception of abundance
BJ =BWFI+0.26×(B−V)J−0.12. (2)
analyses of a few B-type stars by Kornetal. (2002, 2005),
relatively little was known about the spectroscopic content Aftertransformationwefindmean(absolute)differencesof
of NGC2004 until recently. A new survey by Martayanetal. ∼0.05m,withσ ∼0.05mforbothV and(B−V).Inthecentre
(2006),alsowithFLAMES,hasobservedpartofthefieldpop- of LH10, in which there is significant nebular emission, the
ulationnearNGC2004usingthelower-resolutionmodeofthe INT–WFCpipelinedetectedsomeofthesourcesas‘noise-like’
Giraffespectrograph(andwithadifferentfield-centretoours). and did not yield sensible results; for these 11 stars (marked
Martayanetal. concluded that the Be-fraction in their LMC witha∗inTable6)thephotometryhereisthatfromP92.Their
fieldisnotsignificantlydifferenttothatseenintheGalaxy. photometry is also included in the Table for N11-105 which
wasinthegapbetweenCCDsintheWFIV-bandimage.
TheFLAMESobservationsforthecurrentsurveywereob-
tained in service mode and so span a wide range of observa-
2.3. NGC2004photometry
tional epochs, giving reasonable time-sampling for the detec-
tionofbinaries.Therearesurprisinglyfewmulti-epoch,multi- NGC2004wasobservedintwooftheEISpre-FLAMESfields,
objectspectroscopicstudiesofstellar clustersin the literature LMC33and34.AtthetimeoftheFLAMESobservationsafull
inthisrespect,withonesuchstudyin30Doradussummarized EIS data release was notavailable for these fields, so the raw
by Bertrandetal. (1998). Placing a lower limit on the binary imageswereacquiredfromtheESOarchiveandreducedusing
fraction in dense star-forming regions such as NGC346 and theINT–WFCpipeline(alsobyDr.M.Irwin).
N11,combinedwithstellarrotationrates,willhelptoprovide CCD photometry in NGC2004 has been published by
usefulconstraintsinthecontextofstarformationandtheinitial Bencivennietal. (1991) and Balona&Jerzykiewicz (1993).
massfunction. The former study is calibrated to the photographic work of
C.J.Evansetal.:FLAMESSurveyofMassiveStars:LMC&SMCclusters 3
Whilst there is a relatively large scatter in (VJ − VWFI),
thecolourtermisveryrobust;thesameresultisfoundifonly
the photoelecticvaluesare used or, similarly,if onlythe pho-
tographicresults areused. After transformationwe find mean
(absolute)differencesof ∼0.06m, with σ ∼0.04m for both V
and(B−V).
2.4. Selection effects
Following similar methods to those in Paper I for target se-
lection, the photometric data were used to create input cata-
loguesfortheFLAMESFibrePositionerObservationSupport
Software (FPOSS) thatallocates the Medusa fibresin a given
field.
In Paper I we were perhaps too hasty with our descrip-
Fig.1. Comparison of VJ − VWFI with published colours in
tion of avoiding known Be-type stars. To recap, the observed
N11 from Parkeretal. (1992), and primarily from Robertson
samples in the three Galactic clustersfromPaper I were rela-
(1974)forNGC2004.
tivelycompleteforbluestarsin theFLAMESpointing,down
to∼ V=13.Intermsofthefinalsamplesnoexternalselection
effectswerepresentwithregardtoBe-typestars,withonly12
starsclassifiedasBeandoneasAe-type,fromacombinedto-
talof319FLAMESandFEROStargets.Itisworthnotingthat
NGC3293andNGC4755aretwoofthethreeclustersincluded
by Maederetal. (1999) in their ‘inner Galaxy’ sample (with
the lowest Be-fraction compared to normal B-type stars), i.e.
bothNGC3293andNGC4755havegenuinelysmallnumbers
ofBe-typestars.
AsmentionedinPaperI,oneofourprimaryobjectivescon-
cernstheprocessofnitrogenenrichmentinOB-typestarsand
itscorrelation(ornot)withrotationalvelocities.Spectroscopic
analysis of Be stars is more involved (i.e. difficult!) than for
‘normal’ B-type stars. Thus in our FPOSS input catalogue,
in an attempt to ensure that we didn’t observe a preponder-
ance of Be stars in NGC330, we excluded 15 stars classified
Fig.2. Comparison of BJ −BWFI with published colours in as Be-type from previous spectroscopy (Lennonetal. 1993;
N11 from Parkeretal. (1992), and primarily from Robertson Keller&Bessell 1998). However, this isn’t such a strong se-
(1974)forNGC2004. lection effect as it may sound - all of the excluded stars are
fromtheRobertson(1974)surveyandthereforearein(ornear
to)themainbodyofthecluster.ObviouslytheFLAMESsur-
Robertson (1974), albeit with consideration of two of the vey cannot be used to comment on the incidence of the Be-
photoelectricstandardsfromMcGregor&Hyland(1984).The phenomenonintheclusteritself,butitcouldinprincipleoffer
study by Balona&Jerzykiewicz is independentof previously constraintsonthefieldpopulationaroundthecluster.Withre-
published photometry in the cluster, however the ‘finding gard to the non-cluster population, we also excluded 15 stars
charts’andformatofthecatalogue(intermsofpixelpositions) from Evansetal. (2004) that have emission in their Balmer
are less than ideal for successfully recovering matched stars; lines. However, these are not necessarily Be-type stars as the
withoutaccesstotherawframes,accuratecross-matchingbe- narrowemissioninmanyofthestarsfromEvansetal.islikely
tweentheirphotometryandourWFIimagescannotbeensured. attributable to nebular origins(see discussion in their Section
Insteadweemployvisualmatchesof48starsfromtheidenti- 7). Giventhe highdensity of potentialtargetsin the field, the
fication charts of Robertson (1974) to calibrate the WFI data, exclusionofthestarsfromEvansetal.isveryunlikelytobias
takingphotoelectricresultsfromMcGregor&Hyland(1984,2 thefinalsample.
stars)andWalker(1987,7stars),withthedatafortheremain-
InNGC2004,Kelleretal.(1999)reported42Be-typestars
ing39starstakenfromRobertson.TheV andB colourterms
from their photometric study. However, due to the relative
foundfortheNGC2004WFIdataarealsoshowninFigures1
dearth of published spectroscopy in this field at the time of
and2,andthetransformationequationsfoundwere:
ourobservations,nopotentialtargetswereexcludedwhenus-
ing FPOSS for fibre configuration. Lastly, the only weight-
VJ =VWFI−0.03×(B−V)J−0.20, (3)
ing in NGC346 and N11 was to give higherpriority of fibre-
BJ =BWFI+0.29×(B−V)J−0.36. (4) assignmenttoknownOB-typestarsfromMPGandP92.
4 C.J.Evansetal.:FLAMESSurveyofMassiveStars:LMC&SMCclusters
In summary,the onlystrong externalbias in ourobserved The data were reduced using the Giraffe Base-Line
targetswasinthemainbodyofNGC330.Amuchstrongerse- Reduction Software (girBLDRS), full details of which are
lectioneffectinbothNGC330andNGC2004isthatthesheer givenbyBlechaetal.(2003).Forconsistencywithourperfor-
densityoftheclustercorespreventsMedusafibresbeingplaced mance tests in Paper I, v1.10 of girBLDRS was used. More
so close together, with many stellar targets blended – in any recent releases include the option to perform sky subtraction
one FLAMES pointingonly a few stars near the centre could within the pipeline,butwe preferto employthe methodsdis-
be observed with the Medusa fibres. Follow-up of these two cussedinPaperI.
clusters with integral field spectroscopy, such as that offered
Thefinalsignal-to-noiseis,ofcourse,slightlyvariablebe-
byFLAMES-ARGUSatthecentreoftheFLAMESfieldplate,
tween the different wavelength regions for a given target de-
isanobviousprojectto allowa comprehensiveexplorationof
pending on the exact conditions when the observations were
theclusterpopulations.However,thefieldpopulationsofboth
taken. As a guide, the signal-to-noise of the reduced, coad-
NGC330andNGC2004shouldbearelativelyunbiasedsam-
ded spectra is ∼200 for the brightest stars in each field, de-
pleofthetruepopulation,subjecttoclustermembershipissues
creasing to 110 in N11 (with the brightest faint cut-off), 75
andthefaintmagnitudecut-offoftheFLAMESsurvey.These
in NGC2004, and 60 in NGC346. Inspection of the reduced
issuesarediscussedfurtherinSection8.4.
spectra in the NGC330 field revealedparticularlylow signal-
to-noiseinthesixHR03observations.TheSiIIandSiIVlines
thatareimportantforquantitativeanalysisareincludedinthis
3. Observationsanddatareduction
region, so the NGC330 field was reobserved with the HR03
3.1. FLAMES-Giraffespectroscopy setup on 2005 July 20 & 24. These more recent observations
are included in Table A.2 as HR03#07-12. The spectra were
All of the FLAMES observations were obtained in service
reducedusingthesameroutinesandsoftwareastherestofthe
mode,withthe majorityacquiredovera 6monthperiodfrom
survey.
2003 July to 2004 January. The same high-resolution set-
tings were used as for the Galactic observations, i.e. HR02 The NGC330 field features the faintest stars in the entire
(withacentralwavelengthofλ3958A˚),HR03(λ4124),HR04 survey. Besides the problems with the initial HR03 observa-
(λ4297), HR05 (λ4471), HR06 (λ4656), and HR14 (λ6515). tions, the signal-to-noise ratio of the fainter stars in this field
Thebulk ofthe observationsin NGC330were obtainedprior (even in the co-added spectra) decreases to ∼35-40 per un-
to installation of a new grating in 2003 October, so the spec- binned pixel (at V = 16) and down to 25-30 for the very
tral coverageand resolutionof these data are identicalto that fainteststars. Binningof the datahelpsto some degree,butit
ofourGalacticobservations(seePaperI).However,theobser- isclearthatdetailedanalysisofindividualstars(suchasthose
vationsin NGC346,NGC2004and N11 were taken with the presentedby Hunteret al., submitted) will notbe feasible for
new grating in place. The characteristics of the NGC346 ob- some of the faintest targets. Nevertheless, the data presented
servationsaregiveninTable1.Incomparisontotheoldergrat- hereserveasanovelinvestigationofthespectralcontentofthe
ing the effective resolving power is decreased in some setups region.
(in particular in the HR14 setting, yielding a correspondingly
widerwavelengthcoverage),howeverthenewgratingismore
3.2. FLAMES-UVESspectroscopy
efficientintermsofthroughput.
In addition to observationsat 6 central wavelengths, each
InadditiontoobservationswiththeGiraffeSpectrograph,one
field was observed at each wavelength for 6 exposures of
canobserveuptoanadditional6objectssimultaneouslywith
2275s.Therepeatobservationsateachcentralwavelengthwere
the red-arm of UVES (with a central wavelength setting of
takeninbatchesof3exposures,eachtripletforminganobserv-
5200A˚). In the SMC and LMC fields the UVES fibres were
ing block for the ESO service programme.The observational
usedtoobserveasmallnumberof‘red’targets.TheFLAMES-
constraintsonourprogrammewerenotparticularlydemanding
UVES λ5200 set-up gives spectral coverage from approxi-
(therequiredseeingwas1.2”orbetter),butinsomecasesthese
mately λ4200 to 5150and 5250to 6200A˚ (with the break in
conditionswerenotfullysatisfied.Therefore,atsomesettings
coveragearisingfromthegapbetweenthetwo CCDs). These
wehavemorethan6observations,forinstancetheHR14set-
datawerereducedbyDr.A.Kauferusingthestandardpipeline
tingwasobserved9timesinourNGC346field.Althoughthe
(Ballesteretal.2004),whichrunsunderMIDASandperforms
conditionsmaynothavebeenidealforeveryobservingblock,
theextraction,wavelengthcalibration,backgroundsubtraction
all the completedobservationswere reduced– in generalthe
and subsequently merges the individual orders to form two
seeingwasnotgreaterthan1.5”andthedataareofreasonable
continuous spectra, i.e., from λ4200 to λ5150 and λ5250 to
quality. This is of particular relevance in terms of the radial
λ6200A˚.
velocityinformationcontainedinthespectra.Themajorityof
theobservationsinNGC330werespreadoverarelativelyshort Note that these data were observed over multiple epochs,
time(∼10days).Otherwisewehavereasonabletimecoverage, and the pipeline does not correct the spectra to the heliocen-
e.g.theNGC346observationsspannedalmost3monthssowe tric frame. For the purposes of approximate classification the
are in an excellent position to detect both single and double- verylargenumberofindividualUVESspectraweresimplyco-
linedbinaries.InAppendixAwelistthemodifiedJuliandates added,withoutcorrectiontotheheliocentricframe.Therefore
(MJD)ofeachoftheobservations. wedonotquoteradialvelocitiesforthesestars.
C.J.Evansetal.:FLAMESSurveyofMassiveStars:LMC&SMCclusters 5
Table1.Summaryofthewavelengthcoverage,meanFWHMofthearclinesandeffectiveresolvingpower,R,ateachGiraffe
centralwavelengthsetting,λ ,fortheobservationsinNGC346.
c
Setting λc Wavelengthcoverage FWHM R
(A˚) (A˚) (A˚) (pixels)
HR02 3958 3854-4051 0.18 3.7 22,000
HR03 4124 4032-4203 0.15 3.4 27,500
HR04 4297 4187-4394 0.19 3.5 22,600
HR05 4471 4340-4587 0.23 3.7 19,450
HR06 4656 4537-4760 0.20 3.5 23,300
HR14 6515 6308-6701 0.39 3.9 16,700
3.3. AdditionalUVESspectroscopy in N11and MagellanicClouds,arisesfromtheseissues–inalargedataset
NGC330 suchastheFLAMESsurvey,oneshouldbecarefulnottoover-
emphasize groupings as ‘dwarfs’ and ‘giants’, remembering
NormalUVESspectroscopyofafurther14starswasobtained
thatluminosityandgravityarecontinuousquantities.Also,as
in 2001 November 1-3, as part of programme 68.D-0369(A);
inourpreviousstudies,wearecautiouswithregardtoemploy-
thesedataareincludedheretosupplementtheFLAMESsam-
ingtheBenotation–manyofourtargetshaveHαprofilesdis-
ple. The spectra coverλ3750 to λ5000, λ5900 to λ7700, and
playingnarrowcoreemission,accompaniedby[NII]emission
λ7750toλ9600A˚,ataresolvingpowerofR ∼20,000.These
lines which are clearly nebular in origin. Where possible we
datawerealsoreducedusingtheUVESpipeline,contempora-
givepreciseclassificationsfortheBespectra.Inthosespectra
neouslytothosepresentedbyTrundleetal.(2004).
with Fe II emission (discussed further in Section 6) contami-
The9targetsinN11complementtheFLAMESprogramme
nationoflinessuchasSiIII λ4552makesclassificationmore
well,providinganumberofsharp-lined,luminousearlyB-type
difficult.However,asfornormalB-typestars,otherabsorption
spectra.Thespectraofthe5targetsinNGC330wereonlyex-
featuresarealsoofuseastemperaturediagnostics,suchasOII
aminedaftercollationoftheFLAMESdatahencetheirinclu- λλ4415-17andtheOII/CIIIblendatλ4650A˚ (remembering
sion (outof sequence)at the end of Table 5. Note that the 14
toaccountformetallicityeffects).Ofcourse,ourBeclassifica-
stars observedwith UVES in the traditional(non-fibre)mode
tionsdo notconsiderthe likely contributionto the continuum
are marked in Tables 5 and 6 as simply ‘UVES target’ (cf.
bytheemissionregion,andthusmaynotcorrelatetothesame
‘FLAMES-UVES target’ for those observed in the more lim-
temperaturesasfornormalBstars.
ited,fibre-fedmode).
InTables4,5,6,and7wepresenttheobservationalprop-
ertiesofeachofthestarsobservedinthefourFLAMESfields
in the Magellanic Clouds. Spectral classifications and stellar
4. Spectralclassificationsandstellarradial
radial velocities are given, together with cross-references to
velocities
existing catalogues and comments regarding the appearance
The FLAMES spectra were classified by visual inspection, of the Hα profiles and binarity. For NGC346, NGC330 and
largely following the precepts detailed in Paper I, with addi- NGC2004 we also include the radial distance (rd, in arcmin)
tionalconsiderationofthelowermetallicityofstarsintheLMC ofeachstarfromthecentreoftheclustercore.1
and SMC. The principal reference for O- and early B-type Finding charts are included for each of the fields in
spectraisthedigitalatlasfromWalborn&Fitzpatrick(1990), Figures13, 14,15, and16.Thefindingchartsemployimages
withtheeffectsofmetallicityexploredbyWalbornetal.(1995, fromtheDigitizedSkySurvey(DSS)withourtargetsoverlaid.
2000). Later-type stars in the SMC were classified using the TheWFIpre-imagingusedfortargetselectionissignificantly
critieriaoutlinedbyLennon(1997),Evans&Howarth(2003), superiorto the DSS images,howeverour intenthere is solely
andEvansetal.(2004).IntheLMC,A-typesupergiantswere togiveaclearoverviewofthelocationsofeachofthestarsin
classified from interpolation between the Galactic and SMC oursample.TheDSSimagesprovidesuchclarity,inparticular
spectra given by Evans&Howarth, and B-type supergiants theyarefreeofthechip-gapsarisingfromtheWFICCDarray.
were classified with reference to Fitzpatrick (1988, 1991). OneclearpointevidentfromthefindingchartsisthatNGC330
IntermediatetypesofB0.2andB0.7havebeenusedforsome and NGC2004 are very compact clusters and that, whilst the
spectra–theseareinterpolatedtypesthat,inanefforttoavoid FLAMES observations sample some peripheral cluster mem-
metallicity effects, are largely guided by the intensity of the bers,themajorityofthetargetssamplethelocalfieldpopula-
weakHeIIλ4686line. tion.Furthermore,theradiusoftheionizedregioninNGC346
Assignment of luminosity classes in early B-type stars,
1 For completeness, the coordinates (J2000.0) used in calculating
with due attention to metallicity effects and stellar rotation
theradialdistanceswere:
rates, can be difficult. Very subtle changes in the observed NGC346: α=00h59m18.0s,δ=−72◦10′48.0′′,
spectra can yield differentclasses. Indeed, the reason that we NGC330: α=00h56m18.8s,δ=−72◦27′47.2′′,
do not regularly employ the class IV notation for stars in the NGC2004:α=05h30m40.2s,δ=−67◦17′14.3′′.
6 C.J.Evansetal.:FLAMESSurveyofMassiveStars:LMC&SMCclusters
is given by Relan˜oetal. (2002) as ∼3.5 arcmin; many of the betweenopticalandx-raypositionsis0.5′′,suggestingasmall
FLAMEStargetsarebeyondthisradiushighlightingthat,even offsetbetweentheirastrometricsolutionandthatfromtheEIS
in this pointing, the observationssample both the cluster and data. Widening our search radius from 3′′ to 5′′ we find one
fieldpopulation. further potential cross-match: NGC346-078 (an early B-type
The N11 region is more complex, with both LH10 (the binary)is3.8′′fromtheirsource#17;althoughintheopposite
denserregionabovethecentreinFigure15)andLH9(therel- sensetoNGC346-067and#6anditseemsunlikelythatthisis
atively‘open’clusterjustbelowcentre).TheV-bandWFIim- avalidmatch.
age is shown in Figure 17, in false-colour to better highlight Similar searches with the XMM-Newton sources reported
thenebulosity.Thefullcomplexityoftheregionisrevealedin by Naz´eetal. (2004a) in N11, and additional sources in
theoriginalphotographicplatefromHenize(1956).StarN11- NGC346 fromNaz´eetal. (2004b), revealedno furthercross-
004istheprincipalobjectinN11G,N11-063andN11-099are matches with our FLAMES sample, suggesting that none of
both in N11C, and some of our targets south of LH9 are in our observed stars (excepting NGC346-067) are particularly
N11F.Furtherinsightintothestructureofthisregionis given strongx-raysources.
by the Hα+ [N II] photographfrom Malcolm G. Smith pub-
lished by Walborn&Parker (1992), and from a near-IR im- 5. Commentsonindividualstars
agefromDr.R.Barb´a(privatecommunication),bothofwhich
showawidevarietyofarcsandfilamentsofnebulargas. There is a tremendousamountof new spectroscopicinforma-
Radialvelocities(v inkms−1)aregivenforeachstar,ex- tionavailableinourLMCandSMCfields.Innearlyallcases
r
theFLAMESspectraoffersignificantlybetter-qualitydatathan
ceptingthosethatappeartobemultiplesystems.Themeasure-
previously.Also of note is that manystars, particularlyin the
mentsherearethe meansofmanualestimatesofanumberof
NGC330andNGC2004fields,havenotbeenobservedbefore
linecentres,asindicatedinparenthesesinthetables.Thepri-
spectroscopically.
mary lines used are generally those of He I, He II and Si III,
In the following sections we discuss spectra with inter-
with a typical standard deviation of the individual measure-
ments around 5-10 kms−1. We prefer manual measurements esting or peculiar morpholgies. In general we do not address
the specific details of detected binaries, restricting ourselves
such as these becauseof the highlyvariablenebular contami-
to simply indicating their binarity in Tables 4, 5, 6, and 7. In
nationinaregionsuchasNGC346(whichmayledtospurious
many cases the FLAMES spectra are sufficient to determine
results if more automated methods are employed). In a small
orbital periods and, for some systems, offer an insight into
numberof stars with apparentlylargerotationalvelocities(or
the physical nature of the individual components. A compre-
lowersignal-to-noise),precisedeterminationofthelinecentres
hensivetreatmentofthebinaryspectrawillbepresentedelse-
is more difficulttherebyyieldinga less certainvalue, as indi-
where.Emission-line(i.e.OeandBe)starsarediscussedsepa-
catedhereusingtheusual‘:’identifierinthetabulatedresults.
ratelyinSection6.
Theprecisionofmanualmeasurementsmayalsobebiasedby
theinfillingofheliumlines,eitherbynebularcontaminationin
morphologicallynormalspectra, or by infillingof the linesin 5.1. NGC346-001
Be-typestars;wheretheseeffectsareobviouswehaveavoided
NGC346-001isthewell-studiedstarSk80(Sanduleak1968),
therelevantlinesbutnaturallytheremaybecasesinwhichthe
alsoidentifiedasAzV232(Azzopardi&Vigneau1975,1982)
effectsarenotsoprominentyetaffectthe(apparent)linecen-
andMPG789.ItwasclassifiedasO7Iaf+byWalborn(1977),
tre.
withthef+suffixemployedtodenotethestrongSiIVλ4116,
Intables4,5,6,and7wepresentstellarradialvelocitiesfor
N III λ4634-40-42, and He II λ4686 emission features; in-
eachof ourtargets.Inthe processof measuringthe velocities
deed, Sk 80 serves as the principal O7 supergiant in the
wefindarelativelylargenumberofspectradisplayingevidence
Walborn&Fitzpatrick (1990) spectralatlas. A detailed atmo-
ofbinarity.Theseareshowninthetablesas‘Binary’,withSB1
spheric analysis of a VLT-UVES spectrum of this star was
andSB2addedtoindicatesingle-linedanddouble-linedbina-
givenbyCrowtheretal.(2002).
rieswhereitwaspossibletoidentifythenatureofthesystem.
Close inspectionof theindividualFLAMES-Giraffespec-
Finally,inthecommentscolumnofeachtablewenoteasmall
tra revealsseveral features that suggest this object to be a bi-
numberofstarsas‘variablev ?’.Intheseoneortwolineshave
r nary.PerhapsthemostdistinctiveoftheseisshowninFigure3.
anomalousvelocities, with it unclear whether they arise from
Inthefirstfiveexposuresthereisaweakabsorptionfeaturein
binarity.
thebluewardwingoftheHeIIλ4686emissionline(left-hand
panelof figure). Comparethis to the HR06/#06,#07and #08
4.1. Cross-references with x-ray observations framesinwhichitisabsent,withslightlyweakerλ4686emis-
sion (right-hand panel). From the same observations, a small
We have cross-referenced our FLAMES targets in the N11 shift (∼10 kms−1) is seen in the He I λ4713 line. A similar,
and NGC346 fields with the x-ray sources from Naz´eetal. though less significant effect to that seen in the λ4686 line,
(2003, 2004a,b). We find that NGC346-067 is ∼1.9′′ from is also seen in the blueward wing of the Hα profile (we do
source #6 in the Naz´eetal. (2003) study. In fact, it is not consider the core intensity given the problems of nebular
the same counterpart suggested by them, i.e. MA93#1038 subtraction).InspectionofthespectrafromtheHR05observa-
(Meyssonnier&Azzopardi 1993). The tabulated separation tions (whichalso include He II λ4542) revealsa shift of ∼10
C.J.Evansetal.:FLAMESSurveyofMassiveStars:LMC&SMCclusters 7
Fig.3.VariationsintheHeIIλ4686lineseeninNGC346-001. Fig.4. The HR06 observations of NGC346-013. The spectra
TheleftpanelshowsexposureHR06/#02,withtherightpanel from the two epochs have been co-added, and then 11-pixel
showingHR06/#08,notethatthe intensityof the N III λ4634, medianfilteredtoaidclarity.IdentifiedlinesareSiIIIλλ4552-
4640-41 emission is identical whereas the He II λ4686 mor- 68-75;N III λλ4634, 4640-42;C III λ4650;He II λ4686;He I
phologyandintensitydiffers. λ4713. The vertical dotted lines highlight the wavelengths of
theHeIandIIlinesinthesecondbatchofobservations;these
areseentomoveinanoppositesensebetweenepochs.
kms−1betweenthe two epochs,whichis also mirroredin the
HeI λ4471line.Thatthese shiftsareseen inthemainlypho-
tosphericHeIfeaturessuggeststhereisacompanionandthat with a spectral type of B1 or B1.5, but there is also anoma-
wearenotseeingevidenceofwindvariability. lous absorption from He II λ4686. Inspection of the individ-
ComparedtotheVLT-UVESdatafromCrowtheretal.,the ual spectra reveals significant velocity shifts in the He I and
resolvingpower from the high-resolutionmode of FLAMES- Si III absorption lines, with a maximum amplitude over the
Giraffeisroughlyafactoroftwolower,butthesignal-to-noise timecoverageoftheFLAMESobservationsofapproximately
ofthenewspectrumis∼400.Asidefromconsiderationofbi- 400kms−1.OtherlinessuchastheCIIIandNIIIblendsmove
narity, we note the presence of two weak emission lines that inthesamesense.Interestingly,theHeIIλ4686movesinthe
we attribute to N III, with rest wavelengths of λ3938.5 and oppositesense to theotherfeaturesandwith a smaller ampli-
λ4379.0 (Dr. F. Najarro, private communication). Upon rein- tude,suggestingthatitisthemoremassiveobjectinthesystem
spectionoftheUVESspectrumfromCrowtheretal.thesefea- (andpresumablyhotterbyvirtueofthe4686line).Thesefea-
tures can also be seen, but are less obvious due to the inher- turesareillustratedinFigure4.
ent problemsassociated with blaze removaletc. The λ4379.0 Welackotherdiagnosticsofthecompanionassociatedwith
linecanalsobeseeninthehigh-resolutionspectrumpresented the He II λ4686 feature in the current data. The He I λ4471
byWalbornetal.(1995),althoughtherearesomecomparable absorption appears to be marginally double-lined in the first
artifacts nearby; the line is also seen in emission in AzV 83 three HR05 observations, but it is within the noise level pre-
(Walbornetal.2000). ventingaccuratecharacterization.Nostrongabsorptionisseen
fromHe IIλ4542in theHR04 datasuggestinga narrowtem-
peraturerangeforthecompanion.WenotethatNGC346-013
5.2. NGC346-007
does not appear in the x-ray catalogue of Naz´eetal. (2003).
High-resolution optical spectra of NGC346-007 (MPG 324) Amoredetailedtreatmentofitsorbitalpropertieswillbepre-
havebeenpublishedbyWalbornetal.(1995,NGC346#6)and sentedelsewhere.Furtherspectroscopicmonitoringofthisob-
Walbornetal. (2000). In the FLAMES spectrum the Si IV jectisclearlyahighpriority.
λ4116 feature is very weakly in emission (such that it was
within the noise level of previous spectra) and therefore the
5.4. NGC346-026,& NGC346-028
Walbornetal. classification of O4 V((f))isrevisedslightly to
O4V((f+))toreflectthis.Smallradialvelocityshiftsareseen High-resolution echelle spectra of NGC346-026 (MPG 012)
in some lines in the spectra of NGC346-007 (of order 20- and NGC346-028 (MPG 113) were presented by
30kms−1)suggestingitasasingle-linedbinary. Walbornetal. (2000), with a detailed discussion of their
morphologies. For NGC346-028 we adopt the Walbornetal.
classification of OC6 Vz. In the case of NGC346-026
5.3. NGC346-013
we prefer the unique classification of B0 (N str), over the
Thisobjectisoneofthemostintriguingin theFLAMESsur- O9.5-B0 (N str) from Walbornetal. The line that is least
vey.AtfirstglancethespectrumisthatofanearlyB-typestar consistentwithaB0-typeisHeIIλ4200,whichismarginally
8 C.J.Evansetal.:FLAMESSurveyofMassiveStars:LMC&SMCclusters
stronger in NGC346-026 than in υ Ori, the B0 V standard O-typestar.ThiswasconfirmedbyP92,whofoundanembed-
(Walborn&Fitzpatrick 1990) – given the ‘N str’ remark, dedprimary(theirstar 3264)with two faintcompanions.P92
perhaps part of the explanation for this lies with a stronger show the spectrum of 3264 in their Figure 5, classifying it as
λ4200N IIIline.Interestingly,theSiIV linesinthespectrum O3-6 V. The uncertainty in the classification arises from the
are in reasonable agreement with those in υ Ori, which is strongnebularemission inthe spectrum,as onewouldexpect
surprisinggiven the lower metallicity of the SMC. This point from the near-IR study by Israel&Koornneef (1991) who
strengthens the suggestion by Walbornetal. that luminosity concludedthatN11Awasdominatedbysuchemission.
class IV might be more befitting of the star, a priori of the Morerecently,impressiveimagesofN11AfromtheWide
luminosity and gravity results found by Bouretetal. (2003). Field Planetary Camera 2 (WFPC2) on the Hubble Space
Thus,weclassifythestarasB0IV(Nstr). Telescope were published by Heydari-Malayerietal. (2001).
Theirimaging(seetheirFigure2)revealedatleastfiveobjects
in the core of N11A, which they labelled as numbers 5 to 9.
5.5. N11-020
Theirstar#7wasthebrightestwithStr¨omgrenv =14.59,with
The spectrum of N11-020 displays broad, asymmetric Hα threeoftheothers(5,6,and9)fainterthan18thmagnitude.
emission, combined with strong N III λ4634-41 and He II In the WFI imaging used to select our FLAMES targets,
λ4686 emission. Such morphology is similar to that seen in N11A appears as an unresolved, dense blob, with the fibre
ζ Pup (Walborn&Fitzpatrick1990). The FLAMESspectrum placed on the bright core. Our photometric methods here are
appears slightly cooler than ζ Pup, resulting in the classifica- relativelysimpleandwereprimarilyconcernedwithtargetse-
tion of O5 I(n)fp. There are clear variations in both the Hα lection. The multiplicity in N11A, combined with the effects
andHeIIλ4686lines,whichcouldbeindicativeofwindvari- of the nebulosity, highlight that a more tailored photomet-
ability.However,close inspectionof other linessuch as He II ric analysis is warranted for a star such as this, beyond the
λ4542andHδ revealsubtlemorphologicalchangesindicative scope of our programme (and imaging). As such, the quoted
ofacompanion,suggestingthatN11-020isafurtherbinary. magnitude in Table 6 is brighter than that given by P92 and
Heydari-Malayerietal.(2001).
The MEDUSA fibres used with FLAMES have an on-
5.6. N11-026,N11-014& N11-091
sky aperture of 1.2′′. From comparisonswith the figure from
ThespectrumofN11-026isshowninFigure5andisbetween Heydari-Malayerietal.,itislikelythattheMEDUSAfibrewas
the O2 and O3-type standards published by Walbornetal. notcenteredperfectlyontheprincipalstar(owingtothereso-
(2002, 2004). Thus we employ an intermediate type of lutionoftheWFIimage).ItisalsopossiblethattheFLAMES
O2.5 III(f∗). N11-026 is ∼4.5′ to the north of LH10 (see spectrum may include some contribution from their star #8,
Figure15)andthephotographofN11fromWalborn&Parker whichistwomagnitudesfainterthantheprimary.
(1992) shows a likely ionization front just to the east of the TheFLAMESspectrumofN11-028/Parker3264isshown
star. In fact, the FLAMES targets adjacent to #026 offer a inFigure6, andis classifiedhereasO6-8V, cf.O3-6V from
good illustration of the rich star-formation history of the re- P92. We see no obviousevidence of binarity,or of other fea-
gion. Cross-matching our targets again with the image from turesfromapossiblecompanion.TheabsorptionatHeIλ4026
Walborn&Parker (1992), N11-014(to the west of #026)is a islargerthanthatseeninHeIIλ4200,therebyrequiringaspec-
B2supergiantinamorerarefiedregion,andN11-091isanO9- traltypeofO6orlater.Theuncertaintyinthecurrentclassifi-
type spectroscopic binary (with what appears to be a B-type cationarisesbecauseoftheHe Iλ4471line,inwhichthede-
secondary)lyinginadenseknotofgas. greeofinfillingisunclear.Obviouslysucharevisionofspec-
N11-026 has the third largest velocity in the N11 targets, traltypewillhaveasignificanteffectontheperceivedionizing
with v = 330kms−1 (with standard deviation,σ = 5). The fluxinthenebula.Indeed,Heydari-Malayerietal.(2001)con-
r
medianresultfortheN11starswithmeasuredradialvelocities cluded that an O7.5 or O8 main-sequence star could account
is295kms−1suggestingN11-026asarun-awayobject,cf.the fortheobservedionization,commensuratewithourclassifica-
usual critierion of ∆v ∼40 kms−1(Blaauw 1961). N11-026 tion.Oneinterestingfeatureisthe weakMgII λ4481absorp-
r
is∼1′ awayfromN11-091,whichatthedistanceoftheLMC tion sometimesseen in midO-typespectra (e.g.Morrelletal.
correspondsto ∼14pc. An ejected youngstar could conceiv- 1991),attributedbyMihalas(1972)todeviationsfromtheas-
ably cover this distance in its short lifetime (such arguments sumptions of local thermodynamic equilibrium, i.e. non-LTE
arediscussedintheirdefinitionofafieldstarbyMasseyetal. effects.
1995). Indeed, in 2 Myr the star may have even travelled the
∼70pcfromthenorthernedgeofLH10.
5.8. N11-038
Thereisastrikingsimilaritybetweenthespectrumofthisstar
5.7. N11-028
andthatofAzV75intheSMC(Walbornetal.2000),withthe
N11-028 is the primary star of N11A, a well-studied spectrum here classified as O5 III(f+). Interestingly this star
nebular knot to the north-east of LH10 (N11B). was observedby P92 (theirstar 3100)and classified as ‘O6.5
Heydari-Malayeri&Testor(1985)suggestedthattheprincipal V((f)):’. The FLAMES data shows strong He II absorption at
source of ionization was a star with Teff ∼44,000 K, i.e. an λ4200,cf.theP92spectruminwhichitisrelativelyweak.The
C.J.Evansetal.:FLAMESSurveyofMassiveStars:LMC&SMCclusters 9
Fig.5.TwoearlyO-typestars:N11-026andNGC2004-049.ThelinesidentifiedinN11-026are,fromlefttoright,NIVλ4058;
SiIV4089-4116;NVλλ4604-4620;NIIIλλ4634-4640-4642.Forclaritythespectrahavebeensmoothedbya1.5A˚ FWHMfilter.
Fig.6. The FLAMES spectrum of the principalstar in N11A. The He II lines identified are, from left to right, λλ4200, 4542,
4686;thetwostrongestHeIlinesatλλ4026,4471arealsolabelled.Althoughthenebularspectrumsomewhatdominates,there
isstrongabsorptionseeninbothHeIlines,necessitatingalaterspectraltypethanthatadoptedbyParkeretal.(1992).Forclarity
thespectrumhasbeensmoothedusinga7-pixelmedianfilter.
relativeratioofHeIλ4471toHeIIλ4542alsoappearsdiffer- 5.9. N11-040
ent in the P92 spectrum in comparisonto the FLAMES data;
althoughwe see no evidence for binarity in our spectra, vari- Classification of this spectrum was relatively difficult, result-
abilityofthisobjectcannotberuledout. ing in a final type of B0: IIIn. There is apparent emission at
the edge of both wings in the Hα profile. There are also in-
dications of binarity, with the He II lines appearing to have a
slightlylargerradialvelocitythantheotherfeatures,although
N11-038andAzV75areshowntogetherinFigure7.Note thebroadenedlinesmakeprecisemeasurementsverydifficult.
the very weak N IV emission feature in N11-038, also con-
sistent with an early O-type classification. The stronger N III
emission and weaker He II λ4686 absorption in AzV 75 sug- 5.10. N11-045
gestamoreluminousstarthanN11-038,andthesearebourne
outby the brighterV magnitude(taking into accountthe dif- Classified here as O9-9.5 III, the hydrogen and helium spec-
ferent distances and reddening). However we argue that both trumofN11-045isverysimilar to thatofι Ori(O9III)from
starsfallintothesamemorphologicalbin,cf.thestandardsin Walborn&Fitzpatrick (1990). However,we do not rule out a
Walborn&Fitzpatrick(1990). laterO9.5type;veryweakSiIIIabsorptionisseenandtheSiIV
10 C.J.Evansetal.:FLAMESSurveyofMassiveStars:LMC&SMCclusters
Fig.7.TheFLAMESspectrumofN11-038comparedwiththatofAzV75intheSMC, takenfromWalbornetal.(2000).The
linesidentifiedarethesameasinFigures5and6.Forclaritythespectrahavebeensmoothedbya1.5A˚ FWHMfilter.
linesare slightlystrongerthan onewould expectat O9,espe- asB0.2.OfparticularnotearenumerousFe IIemissionlines,
ciallywhenoneconsidersthereducedmetallicityoftheLMC. togetherwithemissionfromothermetallicspecies,e.g.MgII
(λ4481)andSiII(λλ6347,6371).Theλ4300toλ4700A˚ re-
gionofits spectrumisshownin Figure8.Permittedemission
5.11. NGC2004-049
linesfromFeIIareawell-knownphenomenoninsomeBe-type
The spectrum of NGC2004-049 is shown in Figure 5 and is stars (e.g.Wellmann1952;Slettebak 1982),with morethana
classified hereasO2-3III(f∗)+OB;thespectrumis verysim- dozenfoundintheMagellanicCloudsbyMasseyetal.(1995).
ilar to that of LH10-3209 (Parkeretal. 1992; Walbornetal. ThemoststrikingexampleofthesestarsintheFLAMESsur-
2002).TheNIVemissionhasagreaterintensitythantheNIII vey is NGC346-023. Also shown in Figure 8 is another ex-
lines,necessitatinganearlytypeofO2-3fortheprimary.The ample,NGC346-060,inwhichtwin-peakedemissionlinesare
secondarycomponentinNGC2004-049appearscoolerthanin seen, likely indicatinga differentviewingangle.Spectra with
LH10-3209,with the He I λ4471 absorptiongreater than that FeIIinemissionareidentifiedinTables4,5,6,and7as‘Be-
from He II λ4542. Given the relatively weak He II λ4686 in Fe’.TheinterestingOe-typestar,N11-055(seeSection6.3)is
thecompositespectrum,onecanspeculatetherethesecondary alsoshowninFigure8.
doesnotcontributesignificantlyto thislineandthatthecom-
Prompted by the recent study in NGC2004 by
panionisofearlyB-type.
Martayanetal. (2006) we measured the equivalent widths of
Hα emission, EW(Hα), for each of the Be-type FLAMES
5.12. NGC2004-057 spectra. These values were then compared with the presence
or absence of Fe II emission. Given the problems of nebular
Some 5′ east of the cluster, NGC2004-057 (Brey 45;
subtraction with multi-fibre data (which introducesa variable
Breysacher 1981) is a Wolf-Rayet star classified as WN4b
uncertainty, proscribing precise measurements in Be-type
by Smithetal. (1996), in which the ‘b’ denotes broad emis-
stars), we do not tabulate the EW(Hα) values, and limit
sion at He II λ4686. Given the broad nature of the emis- ourselves to a general discussion of the results. Hanuschik
sion features, and the relatively short spectral range of each (1987) reported EW(Hα) = 7 A˚ as the minimum for Fe II to
Giraffewavelength-setting,itisnotpossibletorectifythedata
beseen inGalactic Be stars. With thelowermetallicityinthe
for NGC2004-057 reliably. However, we retain the star in
Clouds one might expect to find that the EW(Hα) threshold
Table 7 as it highlights interesting objects found in the field.
for Fe II emission increases. Martayanetal. (2006) find that
TheFLAMESdataappeartorevealsmallchangesinthestruc-
Fe II emission is seen in their LMC targetswhen EW(Hα) >
tureofemissionlinessuchasHeλ4542,perhapsindicativeof 20A˚, with theinferencethatthishigherthresholdreflectsthe
windvariability.
metallicitydifference.
In our NGC346 and NGC330 fields we find the thresh-
6. Emission-linestars old for Fe II emission is EW(Hα) >15-20 A˚, above which
Fe II emission is seen in all stars (except in NGC346-045).
6.1. Be-type stars
BelowthisthresholdFeIIemissionlinesarenotseenexceptin
The Hα profile of NGC346-023 has asymmetric, double- NGC330-031 [EW(Hα) = 8.5 A˚ (±1)] which has very weak
peakedemission,with infillingin the otherBalmer lines. The Fe II emission atλλ4549, 4556,and 4584.Five of the six Be
absorptionspectrumsuggestsafairlyhotstarandisclassified starsinN11haveFeIIemissionlines(N11-056istheexception