A catalog of planetary nebula candidates and HII regions in NGC 3109

0.2 MB·English

by  M. Pena

Astronomy&Astrophysicsmanuscriptno.pena (cid:13)c ESO2008
February5,2008
A catalog of planetary nebula candidates and HII regions in NGC
⋆
3109
M.Pen˜a1⋆⋆,M.G.Richer2,andG.Stasin´ska3
1 InstitutodeAstronom´ıa,UniversidadNacionalAuto´nomadeMe´xico,Apdo.Postal70264,Me´x.D.F.,04510Me´xico
e-mail:[email protected]
2 InstitutodeAstronom´ıa,UniversidadNacionalAuto´nomadeMe´xico,Apdo.Postal877,Ensenada,B.C.,Me´xico
7
e-mail:[email protected]
0
3 LUTH,ObservatoiredeMeudon,MeudonCedex,France
0
e-mail:[email protected]
2

n Received8November2006/Accepted30December2006
a
J ABSTRACT

0
3 Aims.Imagesobtained withtheESOVLTandFORS1in[O ] 5007 on- and off-band, aswellasr Gunnfilters,areanalyzed to
searchforplanetarynebula(PN)candidates.
2 Methods.In the continuum-subtracted [O ] 5007 on-band images, a large number of emission-line regions were detected. We
v describethecriteriaemployedfordistinguishingPNcandidatesfromcompactHIIregions.
3 Results. Themostunambiguousdiscriminatorsforthetwoclassesofnebulaearethesizesandpropertiesoftheionizingstars.Based
5 uponthesecriteria,wehavefound20PNcandidatesforwhichwepresentcoordinates,nebular[O]fluxes,andstellarmagnitudes.
5 ThecumulativeluminosityfunctionforthesePNeisdiscussed. AcatalogofHIIregionslistingcoordinates,nebular [O]fluxes,
2 stellarmagnitudes,andothercharacteristicsisalsopresented.WefindthatHIIregionsareratherconcentratedtowardsthediskofthe
1 galaxy,whilePNearedistributedalsoaboveandbelowthisstructure,consistentwiththeirbelongingtoanolderstellarpopulation.
6
Keywords.galaxies:individual:NGC3109(DDO236)–ISM:planetarynebulae–ISM:HIIregions
0
/
h
p 1. Introduction Here and in a forthcoming paper, we propose studying the
-
PN and HII region populations in NGC 3109 (DDO 236), a
o
r The dwarf galaxies of the Local Group (LG) and its vicin- Magellanic-typeirregularclassifiedasalate-typespiralSB(s)m
t ity allow detailed studies of their different component popula- (deVaucouleursetal. 1991).NGC3109isthedominantmem-
s
a tions, such as stars, planetary nebulae (PNe), and HII regions. berofthesmallgroupofmetal-poordwarfgalaxiesthatalsoin-
: Therefore,theyprovidestrongconstraintsforstellarpopulation cludesSextansA,SextansB,andAntlia,justattheedgeofthe
v
i studiesandhelpinunderstandinghowtheelementalabundances LG.Duetoitsdistance,NGC3109isparticularlywell-suitedto
X ofgalaxieshavechangedovertime.Dwarfirregulars,inpartic- chemicalevolutionstudiesbecauseitdoesnotseemtohavebeen
r ular,allowacomparativeanalysisofthechemicalpropertiesof affectedbytidaleffectsfromthemassivegalaxiesoftheLG,so
a their stellar, PN, and HII region populations,which providesa itshouldnothavelostasignificantamountofgas.
probeofthechemicalenrichmentandstarformationhistoryof
thegalaxyfromintermediateagestothepresentday.Inaddition, With an absolute magnitude M ∼ −15.2 (see §4) and a
B
throughspectroscopicanalysisofPNeandHIIregionsindiffer- mean oxygen abundance log O/H+12 ∼ 7.75 (as derived from
ent zones of these galaxies, it is possible to address the ques- HII regions by Lee et al. 2003 and, recently, from blue super-
tionofthelarge-scalehomogeneityinthedistributionofheavy giantsbyEvansetal.2006),NGC3109issimilartotheSMCin
elements. To proceed with these studies, the first step is to de- luminosityandchemicalcomposition.Thegalaxyisseenalmost
tectPNeandHIIregions,distinguishingthemfromeachother, edge-on,havinganelongatedshapealignedalmostE-W,withan
whichisanon-trivialmatterinstar-forminggalaxies,beforeob- extensionofabout17.4×3.5arcmin.Studiesofthestellarpopu-
tainingspectrophotometryofthecandidates.Spectroscopicanal- lationsinthisgalaxyhavebeenmadeby,amongothers,Demers
yses have already been done for several galaxies of the Local et al. (1985), who pointed out some traces of spiral structure.
Group. For example, Stasin´ska et al. (1998) present a compar- Sandage&Carlson(1988)reportedlightcurvesandperiodsfor
ative analysis of the PN populationsin the Magellanic Clouds, 29cepheidsandestimatedadistancemodulusof26.0mag(1.59
M32,andthebulgesofthe MilkyWay andM31.M33wasan- Mpc). The cepheidswere revisited by Capaccioli et al. (1992),
alyzed by Magrini et al. (2003), while Sextans A and B were whoderivedadistancemodulusof25.5±0.16(1.26±0.10Mpc),
studiedbyMagrinietal.(2005)andKniazevetal.(2006). and by Musella et al. (1997), who find a distance modulus of
25.67±0.16 (1.36±0.10 Mpc). Based upon V and I band pho-
Sendoffprintrequeststo:M.Pen˜a tometry,Minnitietal.(1999)establishedthepresenceofahalo
⋆ Based on observations collected at the European Southern consisting of Population II stars and derived a distance modu-
Observatory,VLT,Paranal,Chile,programID076.B-0166 lusof25.62±0.1mag(1.33±0.10Mpc)fromadeepluminosity
⋆⋆ On sabbatical leave at the Departamento de Astronom´ıa, function of these stars. We adopt this value for the distance to
UniversidaddeChile. NGC3109inthefollowingsections.
2 M.Pen˜aetal.:AcatalogofplanetarynebulacandidatesandHIIregionsinNGC3109
NGC3109presentsalloftheusualindicatorsofrobuststar ob ID 204406). Each field has dimensions of 6.8×6.8 arcmin
formationactivity:numerousextendedandcompactHIIregions, on the sky (they overlapped by about 2 arcmin in the E-W
large ionized shells, super-shells, and filaments of low surface direction), with a plate scale of 0.2”/pix. For each field, four
brightness.AcatalogofextendedHIIregionswaspublishedby dithered images were acquired with each filter, each with ex-
Hodgein1969.TheOBassociationsandthedistributionofstar- posuretimesof94s(on-band),90s(off-band),and10s(r).The
forming regions were analyzed by Bresolin et al. (1993), who imageswerereducedandcalibratedwiththenormalprocedures
alsoproducedacatalogofHIIregions.Hunteretal.(1993)ana- oftheESOpipeline.Thatis,reducedimagesarebias-subtracted,
lyzedtheshellsandsuper-shellsinthisgalaxy. flat-fielded,andastrometricallycalibrated.Theastrometricpre-
Richer&McCall(1992)reportedthediscoveryofsevenPN cisionis0.2arcsec.
candidatesandtenHIIregionsinthecentralzoneofNGC3109 Each set of four images was combined using IRAF1 rou-
and, from the brightest-PNe method, they derived a distance tines,allowingforcosmicrayremoval.Theresultingimagesare
modulusof25.96(+0.1/−0.4)correspondingto1.6Mpc.From equivalenttoa6.2minexposureforthe[O] on-bandfilter,6
good-quality imaging Pen˜a et al. (2006; and this paper) have minfortheoff-bandfilter,and40sfortherfilter(theseimages
foundthatmostofthePNcandidatesfoundbyRicher&McCall will be available at the CDS). The on- and off-band combined
aremorelikelycompactHIIregionsthataresomewhatbrighter images were subtracted (after backgroundsubtraction and nor-
thanPNe,whichexplainswhytheirdistancemodulusisoveres- malization)toeasilydetect[O]5007emissionobjects.
timatedcomparedtothestellarstudies.Leisyetal.(2005)report Nostandardstarswereobservedforthephotometriccalibra-
thediscoveryof18PNcandidatesinNGC3109and,fromspec- tionoftheimages.Neverthelessin§3weshowthataroughcal-
troscopy,theyfindthatPNedisplayawiderangeofmetallicities. ibrationofthestellarmagnitudescanbeperformedusingsome
Here, we present a deep survey of PNe and HII regions in known stars from the field, and the [O ] on-bandimages can
NGC 3109 based on [O ] 5007 on- and off-band images, as becalibratedusingourspectroscopy.
wellas r Gunnimagingcoveringalmosttheentire galaxy.The
datawereacquiredwiththeESO VeryLargeTelescope(VLT), Thecontinuum-subtracted[O]5007imagesshownumer-
equipped with the Focal reducer spectrograph FORS1. These ous[O ] 5007-emittingobjects.The 7 PN candidatesand the
imagesconstitutethe‘pre-imaging’observationsforthespectro- 10 HII regions reported by Richer & McCall (1992) were re-
scopicprogramID076.B-0166.Theywereobtainedtoidentify covered. At least four of the large shells studied by Hunter et
candidatesforasubsequentmulti-objectspectroscopy.Fromthe al. (1993) are clearly visible; the others are not, probably be-
continuum-subtracted [O ] 5007 images, we identified more causetheyarelowexcitationnebulaethatdonotemitin[O].
than 40 HII regions and 20 PN candidates that are reported in Severalofthe HIIregionsreportedbyHodge(1969)were also
thiswork. identified.Inaddition,anumberofsmalldiffuseHIIregionsex-
The VLT-FORS1 multi-object spectroscopic run associated ist,aswellasmanyunresolvedemittingobjects.Someofthem
with the pre-imaging observations was performed on January coincidewith the Hα emitting objectsin the list from Bresolin
27,2006.SpectraofseveralHIIregionsandPNcandidates,dis- etal.(1993),butthecoordinatesprovidedbytheseauthorshave
tributed in different zones of the galaxy, were acquired. These uncertaintieslargerthan1′′,andsometimesitisdifficulttoiden-
dataallowedustoconfirmthePNnatureofmanyPNcandidates tifytheirobjectswithours.Ourobjectsarepresentedin Tables
and will form the basis of a forthcomingpaper (Pen˜a et al., in 1 and 2, where we have included a column named “other ID”
preparation).Nonetheless the calibrated [O ] 5007 fluxes are listingthenamesgivenbyotherauthorsforthesameobject.
presentedhere,astheyallow usto calibratethe[O ] on-band
imagingandhelptostrengthenourarguments.Inournextpaper, One of the most important issues in studying extragalactic
weshallstudythechemicalabundancesofnebulaeandstarfor- PNe is to distinguish true PNe from compact HII regions and,
mation history of the galaxy,along with the large-scale spatial of course, to avoid contaminationwith backgroundobjects. To
distributionoftheheavyelements. identifyPNeinourimaging,weusedthecriteriadescribedbe-
Thispaperisorganizedasfollows:in§2wepresentthe’pre- low. Criteria (a) and (b) are very similar to those employedby
imaging’ observations and discuss the criteria we use to dis- Soffneretal.(1996)intheirworkonNGC300.
tinguish between planetary nebulae and compact HII regions. a.Objectsize
In §3, we present the properties of the detected PNe and HII AtthedistanceofNGC3109(about1.33Mpc),onearcsec
regions, including positions, diameters, [O ] 5007 calibrated correspondsto6.4pc.Givenourpixelsizeof0.2”/pixandour
fluxes, nebular magnitudes, and V magnitudes for the central FWHMofabout3.2pixforstellarobjects,PNe(whichtypically
stars. ThecumulativeluminosityfunctionforthePNe is calcu- havediameterssmallerthan1pc)shouldappearaspoint-likeob-
latedanddiscussedin§4,andtheconclusionspresentedin§5. jects. Thus,we selectedtheunresolved[O ]-emittingobjects.
These nebulae can be either PN candidates or unresolved HII
regions.
2. Imaging:distinguishingbetweenPNeand
b.Thecentralstar
compactHIIregions HII regions and PNe with significant [O ] 5007 emission
areionizedbystarswithT ≥35,000K(e.g.,Stasin´ska1990).
ThewidefieldcoverageofFORS1allowedustoobservealmost eff
InthecaseofHIIregions,thisimpliesacentralstarofspectral
theentiregalaxywithonlytwoframes.Theobservingprogram
consistedofimagingwiththefilters[O] 5007on-band(filter type O8V or earlier (or O7 if the luminosity class is III or Ia).
name FILT 500 5+85, λ =5000 Å, FWHM=50 Å), [O ] off- Typically,such stars haveabsolute visualmagnitudesof MV ∼
c −4.3to−4.6orbrighter(Martinsetal.2005;Vaccaetal.1996).
band (filter name OIII/6000+52, λ = 5105 Å, FWHM=61 Å)
c
and r Gunn (hereafter r). The images were acquired in service
1 IRAF is distributed by the National Optical Astronomy
modeonNovember29,andDecember1,2005.
Observatories,whichisoperatedbytheAssociationofUniversitiesfor
Two fieldswereobserved,centeredat10:03:19.8-26:09:32 Research in Astronomy, Inc., under contract to the National Science
(eastfield;obID204405)and10:02:54.5-26:09:22(westfield; Foundation.
M.Pen˜aetal.:AcatalogofplanetarynebulacandidatesandHIIregionsinNGC3109 3
Ontheotherhand,thecentralstarsofgalacticPNewithT ≥ image. Magnitudes were determined using the ‘apphot’ pack-
eff
35,000KtypicallyhaveM ∼−2.0(Me´ndezetal.1992),which ageinIRAF.Aperturephotometrywasperformedbyintegrating
V
ismorethan2magfainterthantheionizingstarsofHIIregions. thefluxwithina5pixelradius(equivalentto1arcsec)centered
Adoptingadistancemodulusof25.6magforNGC3109implies onthestellarposition.Thebackgroundwasdeterminedfroman
an apparentvisual magnitude,V, brighterthan about21.3 mag annulus10-13pixelsfromthestarandsubtractedfromtheflux.
fortheionizingstarsin HIIregionsandfainterthanabout23.3 Special care was taken in crowded fields. Instrumental magni-
magforthecentralstarsofPNe. tudes for each object are listed in Tables 1 and 2 for the PN
By measuring the visual magnitudes of the central stars of candidatesandtheHIIregions,respectively.
unresolvedemittingobjects,wecandistinguishcompactHIIre-
gionsfromPNcandidates(seenextsection).Ofcourse,itispos-
3.1.Nebular[O]5007magnitudes
siblethataforegroundorbackgroundstarmayappearprojected
onaPNcandidate.Inthatcase,ourcriterionwouldclassifythe The nebular magnitude, m(5007), was measured from the
i
object as an HII region rather than a PN, and spectroscopy is continuum-subtracted[O]image,therebyexcludingtheemis-
neededtoclassifytheobjectproperly. sion from the central star. The aperture employed includes all
c.Therimages the flux for the nebulae with radii smaller than 1 arcsec, but it
Therfilterhasitsmaximumtransmissionat6530Åandan contains only a fraction of the flux for very extended objects.
FWHM of 810 Å. It therefore includes the stellar flux and the We find that the measured magnitudes for unresolved objects
nebularlinesinthiswavelengthrange.Inparticular,itincludes are well-correlated with the [O ]5007 fluxes measured from
Hα. Thus, we expect the [O ]-emitting objects to appear in ourspectroscopythroughtherelation:
the r images as well. Most of the objects do appear, in which logF(5007)=−0.40mi(5007)−8.32 . (1)
casestheyaremostprobablynotbackgroundemission-lineob- This relation (shown in Fig. 1) has a small dispersion (≤0.05
jects.However,requiringdetectioninboth[O]andrdiscrim- mag)andalargecorrelationcoefficientR2=0.997.Thisimplies
inates against very faint (e.g., Magrini et al. 2001) but highly thattheFORS1pre-imaging,reducedthroughtheESOpipeline
excitedPNethatshouldhavenostellaremissionandforwhich (§2), is very consistent with the calibrated spectrophotometry.
the5007/Hαratioislarge.Therefore,wewillalsoconsiderwith Thus,weareconfidentthatthedifferencesininstrumentalmag-
cautionthosecandidateswithfaint[O],butwhichdonotap- nitudesdorepresentfluxratios.
pearintherimage.
d.Theluminosityofrecombinationlines 3.2.Stellarmagnitudes
Inadditiontothepreviouscriteria,itshouldbetakenintoac-
countthat,ofteninHIIregions,thereismorethanoneionizing Apparentvisualmagnitudesforthecentralstars,mi(star),were
starandthesestarsproducealargernumberofionizingphotons, measured in the off-band frame. A rough photometric calibra-
Q ,duetotheirlargerradius.TypicallylogQ ≥48.0(s−1)for tionusingthesameprocedureasemployedbyRicher&McCall
0 0
HIIregions(Vaccaetal.1996)versuslogQ ∼47.5forPNe(us- (1992) was used to relate these instrumental magnitudes to V
0
ingevolutionarytracksbyBlo¨cker1995).Opticallythickcom- magnitudes. That is, some stars from the list of Demers et al.
pactHIIregionsshouldthenbebrighterthanopticallythickPNe (1985;hereafterDKI)withmeasuredBandVmagnitudeswere
inthehydrogenrecombinationlines.Furthermore,manyPNein usedaslocalstandards.Certainly,a calibrationbaseduponob-
theMilkyWayareknowntobeopticallythin,furtherweakening servationsof photometricstandardswould have been more ap-
these lines.The HαorHβ fluxes(forinstance)can beused for propriate for a photometric calibration; but, as said in §2, our
thiscriterion. imageswere acquiredas ‘pre-imaging’for spectroscopy,so no
standardswereobserved.
e.Theionizationdegreeorexcitationclass
Our off-band instrumental magnitudes follow a linear rela-
Itisexpectedthat,statistically,PNewillbemorehighlyex-
tion with the V magnitudes from DKI, V(DKI), given by the
cited than HII regions as a result of containing hotter ionizing
expression:
stars.IfanebulashowsHe4686emissionwhoseintensityex-
V(DKI)=0.99m(star)+4.38 . (2)
ceedsa few percentofHβ, it isunquestionablya PN.Also, in- i
tensityratios[O]5007/Hβlargerthanabout4arefoundonly This relation is plotted in Fig.1. It has a dispersion ≤0.15 mag
andacorrelationcoefficientR2=0.989.Thegoodcorrelationof
inPNe.However,thiscriteriondiscriminatesagainstPNewhose
the two sets of magnitudes again indicates that differences in
centralstarshavelowT (usuallyyoungPNe).Low-excitation
eff m(star)indeedrepresentfluxratios,whichallowsustoassigna
PNe cannot be distinguished from HII regions on the basis of i
visualmagnitude,V(DKI),tothecentralstarsofourHIIregions
onlytheirspectroscopiclineratios.
andcandidatePNe.
We also measured the instrumental r magnitude, m(r). As
i
From the above criteria, a and b are clearly the least ambigu-
alreadynoted,m(r)includesthestellarfluxandthenebularlines
i
ousindistinguishingbetweencompactHIIregionsandPNcan-
intherfilter,particularlyHα.Consequently,objectswithbright
didates, when only imaging is available. The outcomes of our
m(r)magnitudeshaveveryintenseHαorabrightstar.
imaging analysis, upheld with the [O ] fluxes from our spec- i
troscopy,arepresentedinthefollowingsections.
3.3.PNeandHIIregionsinNGC3109
Wehaveclassifiedthediffuseandextendedemissionnebulaeas
3. Nebularandstellarmagnitudes
HIIregions.Inthecaseofthecompactobjects,weseparateHII
Forallof our[O] emittingobjects,we havedeterminedsev- regionsfromPNcandidatesusingthemagnitudesoftheirioniz-
eral instrumental magnitudes: the nebular magnitude m(5007) ingstars.Consideringthatthevisualmagnitudesoftheionizing
i
fromthecontinuum-subtractedon-bandimage,thestellarmag- starsinHIIregionsshouldbebrighterthanabout21.4mag(§2,
nitude m(star) from the off-band image, and m(r) from the r b),equivalentto17.2maginoursystem,weconsiderallobjects
i i
4 M.Pen˜aetal.:AcatalogofplanetarynebulacandidatesandHIIregionsinNGC3109
Fig.2. The color index m(r)−m(star) plotted against m(star).
i i i
OpensquaresrepresentHIIregions(objectswithm(star) ≤18
i
mag).Black dotsrepresentPN candidates.Sincerincludesthe
fluxfromthestarandHα,thecolorindexisproportionaltothe
flux ratio (F(Hα)+F (star))/F(star). Thus, objects with a very
r i
faint central star (e.g., PNe) appear in the lower right corner.
Thevaluesm(star)=22areupperlimits. Fortheseobjects,the
i
starwasnotdetected.Thearrowsshowthedisplacementofdots
forstarswithfainterm .
r
(Pen˜a et al., in preparation), while column 9 lists the value of
log F(5007) calculated from Eq. (1). In column 10, any previ-
ousidentificationsare listed. As alreadyreportedin Pen˜a et al.
(2006),weconfirmasPNeonlytwoofthesevenPNcandidates
Fig.1.Therelationsbetweenourinstrumentalm(5007)andthe foundbyRicher&McCall(1992).
i
spectroscopic [O ] 5007 flux, F(5007),(upperpanel) and be- Table2liststhecharacteristicsoftheHIIregions.Wepresent
tweenm(star)andV(DKI)forsomestars(lowerpanel). coordinates, diameters, magnitudes, and fluxes for 40 nebulae
i
foundinourcontinuum-subtracted[O] image.Thisisnotan
exhaustive list of HII regions in NGC 3109, but it includes a
with m(star) brighter than 18 mag as HII regions. This limit- largefractionofthe[O]5007emittingregions.Theverylow
i
ingmagnitudeallowsforanuncertaintyof0.3maginindividual excitation nebulae without 5007 emission are obviously not in
instrumental magnitudes (twice the dispersion of Eq. (2)) and this list, and some detected but very faint HII regionsand fila-
an extinctionof upto 0.5mag,a valuethatamplyincludesthe mentswerenotincluded.Them(star)andV(DKI)magnitudes
i
small color excess of E(B-V)= 0.04 mag (equivalent to A = measured for the central star of the HII regions(when there is
V
0.13 mag, see §4) reportedby Burstein & Heiles (1984)in the an obvious central star) are presented in columns 6 and 7, re-
directionofNGC 3109andany plausibleinternalextinctionin spectively. In column 8 we list m(r). The [O ] 5007 fluxes,
i
the HII regions. We note that some ionizing stars, in both HII F(5007),fromspectroscopyandcalculatedviaEq.(1)arelisted
regionsand PNe, couldbe binaries, in which case m(star) and in columns 9 and 10, respectively. The other columns contain
i
V(DKI)representthefluxesofbothstars. Consideringthepos- a description of the morphology (diffuse, compact, extended,
sibility of binarity, our limiting magnitude for separating PNe complex, unresolved), a rough estimate of the stellar spectral
fromHIIregionsisthenquiteconservative. type(seebelow),andpreviousidentificationsoftheHIIregions
In Fig. 2,we presentthecolorindexm(r)−m(star) plotted (columns11-13,respectively).
i i
asafunctionofm(star)forHIIregions(objectswithm(star)≤ In Fig. 3 we present our [O ] 5007 image of NGC 3109.
i i
18)andPNcandidates(withm(star)>18).ThecolorsofHIIre- In this figure, we show the distribution of PNe from Table 1
i
gionsspantheintervalfrom−1.5to0.8mag.ForPNcandidates and compact HII regions from Table 2. Our objects are spread
the colors are bluer (more negative) than −1.3. The two types throughoutthegalaxy,anditisevidentthatHIIregionsarerather
ofnebulaeareseparatedverynicelyinthisfigure.Thissepara- concentratedtowardstheedge-ondiskofthegalaxy,whilePNe
tionoccursbecausethecolorindexm(r)−m(star)corresponds areseenalsoaboveandbelowthisstructure,consistentwiththeir
i i
roughlytothefluxratios(F(Hα)+F (star))/F(star),whichwill belongingtoanolderstellarpopulation.
r i
be largeforPNe while,atthe same time, theircentralstarsare
faint.
3.4.IndividualPNe
In total, we detected 20 PN candidates. Their characteris- a.ThebrightestPN
tics are listed in Table 1, where we include their coordinates Accordingto ourselection criteria,ourPN7 andPN10are
(columns2and3)andmagnitudesm(5007),m(star),V(DKI), the only bona fide PN candidates from the list reported by
i i
and m(r) (columns 4 to 7, respectively). Column 8 presents Richer & McCall (corresponding to their PN1 and PN6, re-
i
logF(5007),inergcm−2s−1,fromoursubsequentspectroscopy spectively).PN10isabrightPNwithnostellarcontinuum,but
M.Pen˜aetal.:AcatalogofplanetarynebulacandidatesandHIIregionsinNGC3109 5
Table1. PositionsandcharacteristicsofPNcandidatesinNGC3109a
Name R.A.b Decb m(5007) m(star)c V(DKI) m(r)c logd loge otherIDf
i i i
F(5007) F(5007)
PN1 10:02:41.57 -26:08:40.7 19.0 >22 >25 >22.5 −15.91
PN2 10:02:44.70 -26:11:32.4 19.7: 21.0: 25.1: 17.8 −16.21
PN3 10:02:49.15 -26:09:10.1 16.4 >22 >25 18.8 −14.88 −14.89
PN4 10:02:50.06 -26:08:10.0 17.3 >22 >25 >22.5 −15.25 −15.23
PN5 10:02:51.60 -26:10:19.7 18.7 21.0: 25.1: 17.1 −15.81
PN6 10:02:57.20 -26:08:55.8 18.7 19.5 23.6 17.9 −15.81
PN7 10:02:58.20 -26:08:45.8 14.4 18.2 22.4 15.8 −14.09 −14.09 PN1RMc
PN8 10:02:59.52 -26:08:13.9 18.9 20.0 24.1 17.4 −15.89
PN9 10:03:02.66 -26:08:50.3 16.4 >22 >25 19.7 −14.88
PN10 10:03:03.91 -26:09:42.3 15.4 >22 >25 18.4 −14.48 PN6RMc
PN11 10:03:05.04 -26:10:54.2 15.6 >22 >25 18.0 −14.52 −14.57
PN12 10:03:07.99 -26:07:57.8 18.8 19.40 23.5 16.5 −15.21
PN13 10:03:08.52 -26:09:07.7 17.2 >22 >25 >22.5 −15.15
PN14 10:03:10.34 -26:08:06.1 18.5 19.5 23.2 17.1 −15.78 −15.71
PN15 10:03:13.32 -26:10:20.7 19.3 >22 >25 >22.5 −16.04
PN16 10:03:18.67 -26:09:58.8 17.0 >22 >25 18.6 −15.13
PN17 10:03:18.74 -26:10:05.4 16.7 18.8 23.0 17.5 −14.96 −15.01
PN18 10:03:20.74 -26:09:00.2 17.5 >22 >25 >22.5 −15.32
PN19 10:03:21.22 -26:11:20.9 19.1 >22 >25 >22.5 −15.98
PN20 10:03:25.51 -26:09:07.2 17.0 18.6 22.8 16.8 −15.13
(a)Alltheseobjectsareunresolved.
(b)Coordinatesforequinox2000.
(c)Objectswithm >22arenotdetectedintheoff-bandimage.Objectswithm(r)>22.5arenotdetectedintherimage.
i i
(d)Fluxfromspectroscopy,inergcm−2s−1.
(e)FluxcalculatedfromEq.(1),inergcm−2s−1.
(f)RMc:Richer&McCall1992.
Fig.3.Our[O]on-bandimage,showingthewholegalaxy.Northisup,eastisleft.Thefullsizeoftheimageis16.7×5.3arcmin.
PNcandidatesfromTable1aremarkedwithacircle.CompactHIIregionsfromTable2aremarkedwithasquare(squareswithan
innercircleindicatetheobjectsreportedbyRicher&McCall1992).TheHIIregionsareratherconcentratedtowardstheedge-on
diskofthegalaxy,whilePNespreadoverawiderarea.Thelargecircles,fromlefttoright,showtheshells#1,3,5,and9studied
byHunteretal.(1993).
PN7 has the brightest central star among our PN candidates, showsaveryhigh5007/Hβratio(Pen˜aetal.,inpreparation).In
with V(DKI)=22.4 mag, i.e., brighter than expected for a sin- addition, it shows a [O ] 5007 line width, HWHM = 13 km
glestar (§2,criterionb).Thisnebulais alsothe brightestin [O s−1 (Richer 2006), which is significantly greater than the val-
]5007,onemagnitudebrighterthanthenextbrightestobject. uesofHIIregions.Forcomparison,theaverage[O]5007line
We included it in the PN group due to its spectroscopy,which width(HWHM)ofthefivePNcandidatesfromRicher&McCall
6 M.Pen˜aetal.:AcatalogofplanetarynebulacandidatesandHIIregionsinNGC3109
(1992)thatwefindarecompactHIIregionsis11kms−1(Richer Table3. FitforthecumulativePNLF
2006;Richeretal.inpreparation).Alsoin§4wepresentfurther
argumentsforincludingitamongthePNsample. fit m∗ Nexp(−0.307µ)
5007
b.ThePNewithnoorveryfaintremission includingPN7 21.18 2.62×10−3
Six PNcandidatesinoursamplewerenotdetectedinourr excludingPN7 21.82 2.77×10−3
LMCa 14.23 0.287
image. They are PN1, PN4, PN13, PN15, PN18, and PN19.
SMCa 14.82 9.31×10−2
Wedeterminedaninstrumentalupperlimitof22.5magfortheir
m(r).Severalofthemarealsoveryfaintin[O].Asmentioned M31b 20.20 0.150
i
in §2 (criterion c), these objects are considered PN candidates
(a)BaseduponthesampleofJacobyetal.(1990)and
butsomeofthemcouldbebackgroundsources.Mostprobably,
consideringthesamelimitingmagnitude,15.9mag,forfitting.
though,theyarehighexcitationPNewhere[O]5007ismuch
(b)BaseduponthesampleofCiardulloetal.(2002)and
strongerthanHα.Fromourspectroscopy,wehaveverifiedthat
fittingtothefirstthreemagnitudesoftheluminosityfunction.
atleastPN4isatruePN(Pen˜aetal.,inpreparation).
Fitzpatrick (1999) reddeninglaw, parametrized with a total-to-
3.5.ThestellarspectraltypesinHIIregions
selectiveextinctionof3.041.Thisparametrizationdeliversatrue
OntheV(DKI)magnitudescale,thecentralstarsofHIIregions ratiooftotal-to-selectiveextinctionof3.07whenintegratedover
showvaluesintherangefrom22.1to19.5,anda spectraltype thespectrumofVega(McCall2004),whichistheaveragevalue
canbeassignedtoeachthembyadoptinganabsolutemagnitude forthediffusecomponentoftheinterstellarmediumoftheMilky
scaleformassivestars(forinstanceVaccaetal.1996orMartins Way (McCall & Armour 2000). The extinction towards NGC
etal.2005)andadistancemodulus.Wechosethedistancemod- 3109thenamountsto A5007 = 0.13mag.Ourfittothecumula-
ulus,m-M=25.62mag(Minnitietal.1999).Thisexercisewas tiveluminosityfunctionreturnstheproductNexp(−0.307µ)and
done only for those relatively small HII regionswhere there is m∗ as fitting parameters.Althoughthis allows us to derive a
5007
anobviouscentralstar.Extendednebulae(complexregionsand normalization constant without knowledge of the peak magni-
loops)appearrelatedtostellarclumpsanditisverydifficultto tudeoftheluminosityfunction,itobviouslyprecludesusingour
decidewhichonesaretheionizingstars;thereforeforthemwe peakmagnitudetoderiveadistancetoNGC3109,asisusually
havenottriedtoidentifytheionizingstars.Anotherproblemis done.
theassumptionthatthesestarsaresingle,whichlikelybiasesour Since the brightestPN (PN7 in Table 1, see §3.4)is 1mag
classificationsto earlier spectraltypes.In anycase, these spec- brighterthanthenextbrightestobject,wefitthecumulativelu-
tral types (column 9, Table 2) are very rough approximations minosity function while both including and excluding this ob-
thatshouldbeconsideredmerelyindicative.Inaddition,nored- ject. Both fits to the luminosity functionare similarly good, so
deninghasbeenassumednorhasanyaccountbeentakenofany the luminosity functionprovidesno groundsfor excludingthis
possiblemagnitudeoffsetoftheDKIcalibration(Bresolinetal. objectasa PN.Theparametersforthese fitsaregiveninTable
1993 claimed a difference of about 0.3 - 0.4 mag). From this 3, where we also provide similar fits to the cumulative lumi-
roughapproximationwedetectafewgiantsandsupergiantstars nosity functions for PNe in the Magellanic Clouds and M31
(spectraltype O III or O Ia), five main sequencestars between forcomparison.OurapparentpeakmagnitudesforM31andthe
O4andO6,fiveO6-O7,and16starslaterthanO7. Magellanic Clouds are within 0.12mag of those found in the
originalstudies(seeCiardulloetal.1989forM31),adifference
thatfallswithintheuncertaintiesinallofthesestudies,including
4. TheluminosityfunctionforPNe ours.
Considering the brightest PN candidate as a bona fide PN,
Fromour[O ] fluxes,F(5007)(Eq.1;column9, Table 1),an
we can use the true distance modulusof 25.62mag (Minnitiet
apparentmagnitudem can be obtainedand the [O ] 5007
5007 al.1999)andtheextinctionA =0.13toderiveapeakabsolute
5007
luminosity function (PNLF) can be constructed. In Fig. 4, we magnitudeoftheluminosityfunctionofM∗ =−4.57 magfor
present the cumulative luminosity function for our PN candi- 5007
NGC3109.Thisvalueissurprisinglybrightatthemetallicityof
dates (including PN7, see below). We chose this representa- thisgalaxy,comparedwiththevalueof−4.48magsuggestedby
tion because of the low number of PN candidates and because
Ciardulloetal.(2002)fromstudiesofseveralgalaxiesofhigher
the peak magnitude of the luminosity function is poorly con-
metallicity. On the other hand, excludingthe brightestPN, our
strainedatthemetallicityofNGC3109(Ciardulloetal.2002).
fittotheluminosityfunctionimpliesapeakabsolutemagnitude
Therefore,wemustfitthecumulativeluminosityfunctionusing ofonly−3.93mag,avaluethatisfaintcomparedtothevaluesof
apparentmagnitudes,insteadoftheusualabsolutemagnitudes.
about−4.08magexpectedbyCiardulloetal.(2002)forgalaxies
Weconverttheusualluminosityfunction withmetallicities12+logO/H∼8.0.Obviously,oneoftheben-
N(M)∝exp(0.307M )(1−exp(3(M∗ −M )))
5007 5007 5007 efits of observing low metallicity galaxies like NGC 3109 will
toaluminosityfunctioninapparentmagnitudes be a better understanding of the absolute luminosities of their
N(m)=Nexp(−0.307µ) exp(0.307m5007)(1−exp(3(m∗5007− planetarynebulae.
m5007)), BaseduponthenormalizationfactorsinTable3,NGC3109
whereN isa normalizationconstant,µis theapparentdistance has about the expected number of PNe. Adopting a true dis-
modulus, µ = 5logd−5+ A5007, M5∗007 and m∗5007 are the ab- tancemodulusµ0=18.50magandA5007=0.36magfortheLMC
soluteandapparentpeakmagnitudesoftheluminosityfunction, (Jacobyetal.1990)andµ =25.62magandA =0.13magfor
0 5007
respectively,thelatterdefinedvia NGC3109,wefind N = 93.85and N = 7.11fortheLMCand
m5007=−2.5logF(5007)-13.74 NGC3109,respectively.IfweadopttheabsoluteBmagnitudes
(Allen 1973;Jacoby 1989),and A5007 is the extinction at 5007 fromRicher&McCall(1995),butcorrectthemtothedistance
Å towards NGC 3109. For the extinction, we adopted the moduli already mentioned, the luminosity ratio is 11.69, very
aforementioned color excess, E(B − V) = 0.04mag, and the similartotheratioofNvalues,13.20.Therefore,NGC3109has
M.Pen˜aetal.:AcatalogofplanetarynebulacandidatesandHIIregionsinNGC3109 7
30 3109hasaboutthesamenumberofPNeperunitluminosityas
the LMC. By assuming a true distance modulus of 25.62 mag
NGC 3109 andanextinctionA =0.13magforNGC3109,a peakvalue
25 PNLF fit 5007
LMC, scaled of −4.57mag is derivedfor the PNLF. This valueis high com-
)
e paredbothwiththecanonical−4.48magfoundforgalaxieswith
v
ti 20 highermetallicityandwith thepeakmagnitudeexpectedatthe
a
ul metallicityofNGC3109.Bystudyingmoregalaxieswithmetal-
m
cu 15 licitiessimilartoNGC3109’s,abetterunderstandingoftheab-
( soluteluminositiesoflowmetallicityPNewillbeacquired.
)
e
N 10 Acknowledgements. M. Pen˜a is grateful to the Departamento de Astronom´ıa,
P Universidad de Chile for hospitality during a sabbatical stay when part of
(
N thisworkwasperformed.M.P.gratefullyacknowledgesfinancialsupportfrom
FONDAP-ChileandDGAPA-UNAM.Wethankthereferee,Dr.MarioPerinotto,
5
forhisconstructivecomments.Thisworkreceivedfinancialsupportfromgrants
#43121(CONACyT-Mexico),IN-108506-2,IN-108406-2,IN-112103,andIN-
114805(DGAPA-UNAM).
0
0 1 2 3 4 5 6
m5007 - m*5007 (mag) References
Fig.4. Cumulative planetary nebula luminosity function from Allen,C.W.1973,AstrophysicalQuantities(London:Athlone)
the data in Table 1. The fit to the cumulativePNLF returnsthe Blocker,T.1995,A&A,299,755
product Nexp(−0.307µ) and m∗ (see text and Table 3). The Bresolin,F.,Capaccioli,M.,&Piotto,G.1993,AJ,105,1779
5007 Burstein,D.,&Heiles,C.1984,ApJS,54,33
LMC’sluminosityfunction,scaledbya factorof1/13.2is also
Buzzoni,A.,Arnaboldi,M.,&Corradi,R.L.M.2006,MNRAS,368,877
presented.
Capaccioli,M.,Piotto,G.,&Bresolin,F.1992,AJ,103,1151
Ciardullo,R.,Jacoby,G.H.,Ford,H.C.,&Neill,J.D.1989,ApJ,339,53
Ciardullo,R.,Feldmeier,J.J.,Jacoby,G.H.,etal.2002,ApJ,577,31
aboutthesamenumberofPNeperunitluminosityastheLMC. DemersS.,KunkelW.E.,&IrwinM.J.1985,AJ,90,1967(DKI)
deVaucouleursG.,deVaucouleursA.,CorwinH.G.,etal.1991,Thirdreference
Thisisexpected,sincethecolorsoftheLMCandNGC3109are
catalogueofBrightGalaxies(Springer,NewYork)
similar(Buzzonietal.2006).
Evans, C. J., Bresolin, F., Urbaneja, M. A., Pietrzyn´ski, G., Gieren W., &
InFig.4,weoverlaytheLMC’sluminosityfunction,scaled Kudritzki,R.-P.2006,acceptedbyApJ,astro-ph/0612114
by 1/13.2. Both fits (NGC 3109’s and LMC’s) show excellent Fitzpatrick,E.L.1999,PASP,111,63
agreementoverthefirst1.5−2.0mag,theextentoverwhichthe Hodge,P.W.1969,ApJS,18,73
Hunter,D.A.,Hawley,W.N.,&Gallagher,J.S.III1993,AJ,106,1797
LMC’s luminosity function is believed to be complete (e.g.,
Jacoby,G.H.1989,ApJ,339,39
Richeretal.1997).Sincethenormalizationofthetwofitstothe Jacoby,G.H.,Walker,A.R.,&Ciardullo,R.1990,ApJ,365,471
luminosityfunctionaresimilar(Table2),regardlessofwhether Kniazev, A. Y., Grebel, E. K., Pramskij, A. G., & Pustilnik, S. A. 2006, in
PN7isconsidered,theconclusionthatNGC3109hasaboutthe PlanetaryNebulaeBeyondtheMilkyWay,eds.L.Stanghellini, R.Walsh
andN.G.Douglas(Springer:Berlin,Germany),257
numberofPNeexpectedisindependentofwhetherPN7mayor
Lee,H.,McCall,M.L.,&Richer,M.G.2003,AJ,125,2975
maynotbeatruePN. Leisy,P.,Magrini, L.,Corradi, R.L.M.,&Mampaso, A.2005, in Planetary
NebulaeasAstronomicalTools,eds.R.Szczerba,G.StasinskaandS.Gorny
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Magrini,L.,Perinotto,M.,Corradi,R.L.M.,&Mampaso,A.2001,A&A,379,
90
5. Conclusions
Magrini,L.,Perinotto,M.,Corradi,R.L.M.,&Mampaso,A.,2003,A&A,400,
From[O]5007on-band,off-band,andrimaging,wedetected 511
Magrini,L.,Leisy,P.,Corradi,R.L.M.,etal.2005,A&A,443,115
a large number of extended and compact emitting nebulae in Martins,F.,Schaerer,D.,&Hillier,D.J.2005,A&A,436,1049
NGC3109.WehavedefinedcriteriatodistinguishbetweenPN McCall,M.L.2004,AJ,128,2144
candidatesandcompactHIIregions,whichallowustoidentify McCall,M.L.,&Armour,M.-H.2000,inMappingtheHiddenUniverse:The
20PNcandidates,forwhichwepresentcoordinates,[O]5007 UniverseBehind theMilkyWay–TheUniverse inHI,ASPConf.Ser.,
eds.R.C.Kraan-Korteweg,P.A.Henning,&H.Andernach(SanFrancisco:
magnitudes,andstellarmagnitudes,whenthecentralstarisde-
AstronomicalSocietyofthePacific),218,1
tected. We also present a catalog of 40 HII regions (extended Me´ndez,R.H.,Kudritzki,R.,&Herrero,A.1992,A&A,260,329
andcompact)thatincludescoordinates,diameters,[O ] 5007 Minniti,D.,Zijlstra,A.A.,&Alonso,M.V.1999,AJ,117,881
magnitudes, and instrumental magnitudes for the central stars. Musella,I.,Piotto,G.,&Capaccioli,M.1997,AJ,114,976
Pen˜a,M.,Richer,M.G.,&Stasin´ska,G.2006,inPlanetaryNebulaeintheMilky
ApparentVmagnitudeshavebeenestimatedfromaroughpho-
WayandBeyond,IAUSymp.234,eds.M.J.Barlow andR.H.Me´ndez
tometriccalibrationoftheinstrumentalmagnitudes.Basedupon (CambridgeU.Press:Cambridge,UK),inpress
theseVmagnitudes,weassignaroughspectralclasstotheion- Richer,M.G.2006,inPlanetaryNebulaeintheMilkyWayandBeyond,IAU
izingstarsofHIIregions. Symp. 234, eds. M. J. Barlow and R. H. Me´ndez (Cambridge U. Press:
Cambridge,UK),inpress(astro-ph/0605348)
The distribution of HII regions is concentratedtowards the Richer,M.G.,&McCall,M.L.1992,AJ,103,54
Richer,M.G.,&McCall,M.L.1995,ApJ,445,642
edge-on disk of the galaxy, while PN distribution is more ex-
Richer,M.G.,McCall,M.L.,&Arimoto,N.1997,A&AS,122,215
tended,coveringawiderarea,aboveandbelowthedisk.Thisis
Sandage,A.,&Carlson,G.1988,AJ,96,1599
consistentwiththePNebelongingtoanolderstellarpopulation. Soffner,T.,Me´ndez,R.H.,Jacoby,G.,Ciardullo,R.,Roth,M.M.,&Kudritzki,
R.P.1996,A&A,306,9
Stasin´ska,G.1990,A&ASupl.Ser.,83,501
ThecumulativePNLFfor[O]5007magnitudeswascon- Stasin´ska,G.,Richer,M.G.,&McCall,M.L.1998,A&A,336,667
structedandafittothisfunctionwascalculated.Comparingthis Vacca,W.D.,Garmany,C.D.,&Shull,J.M.,1996,ApJ,460,914
fitwithafittotheavailabledatafortheLMCshowsthatNGC
Table2.PositionsandcharacteristicsofHIIregionsinNGC3109 8
Name R.A.(2000) Dec(2000) φ(”) m(5007) m(star) V(DKI)a m(r) logFb logFb descriptionc S.T. otherIDd
i i 5007 5007
HII1 10:02:46.50 -26:10:10.0 >60 — — — — — cmplxloop clump Ho19;Hu9;F3H1,F3H2,..
HII2 10:02:49.35 -26:08:38.1 5.7 18.6: 16.9 21.0 16.7 −15.8: diff O7-O8V F2H4
HII3 10:02:50.50 -26:08:48.5 5.2 18.8: 16.2 20.4 16.5 −15.9: diff O4-O5V F2H5
HII4 10:02:50.66 -26:09:35.9 1.1 14.7 16.1 20.2 15.6 −14.21 comp O4-O5V nearF2H7
HII5 10:02:50.89 -26:09:35.9 4.0 15.9 17.3 21.5 17.4 −14.70 diff O8V nearF2H7
HII6 10:02:52.03 -26:09:05.3 0.8 14.2 16.6 20.8 15.5 −14.02 comptail O6-O7V F2H3
HII7 10:02:52.46 -26:09:24.6 1.4 14.4 16.5 20.7 15.8 −14.11 −14.10 comp O6-O7V nearF2H6
M
HII8 10:02:56.28 -26:08:58.3 17.0 15.3 15.7 −14.45 ext clump HII1RMc;Ho12;F1H4,H12 .
P
HII9 10:02:58.11 -26:08:52.5 5.0 17.2 17.2 21.4 17.2 −15.21 diff O8-O9V e
˜n
HII10 10:02:58.91 -26:08:48.3 13.0 16.1 15.9 20.1 16.1 −14.79 ext O7III HII2RMc;Ho11 a
e
HII11 10:02:59.16 -26:09:17.5 <0.8 15.0 17.0 21.2 16.0 −14.32 −14.33 unres O8-O9V PN2RMc ta
HII12 10:02:59.52 -26:09:46.6 4.7 15.9 16.7 20.9 16.9 −14.69 diff O7-O8V HII3RMc l.:
A
HII13 10:03:00.12 -26:08:53.3 20.0 — — — — — extloop clump Ho8;HII4RMc;Hu5 c
a
HII14 10:03:00.19 -26:09:28.7 0.8 15.4 16.0 20.2 15.6 −14.48 comp O6III PN3RMc ta
HII15 10:03:01.34 -26:09:27.2 <0.8 14.3 16.5 20.7 15.8 −14.11 −14.06 unres O5-O6V PN4RMc log
HII16 10:03:01.37 -26:08:38.3 8.5 15.3 15.0 19.2 15.6 −14.45 ext OIa HII5RMc,F1H3 of
HII17 10:03:01.97 -26:08:37.5 <0.8 15.2 17.2 21.4 16.1 −14.42 −14.42 unres O8-O9V PN5RMc pla
HII18 10:03:03.77 -26:09:20.7 13.0 15.4 15.3 19.5 15.2 −14.48 ext clump HII6RMc,D2H5 ne
HII19 10:03:04.46 -26:08:43.9 3.0 15.7 — — — −14.61 diff — HII7RMc tar
y
HII20 10:03:04.54 -26:09:20.7 1.6 14.3 16.4 20.6 15.7 −14.09 −14.05 comp O6-O7V PN7RMc n
e
HII21 10:03:05.16 -26:09:23.8 4.0 16.0 15.5 19.7 16.1 −14.73 diff O5III HII8RMc bu
HII22 10:03:08.50 -26:10:02.5 60.0 — — — — — arc — D2H4;Hu3 la
c
HII23 10:03:10:67 -26:09:25.9 8.0 18.0 16.1 20.3 16.1 −15.54 diff O4-O5V an
d
HII24 10:03:11.50 -26:10:22.4 1.2 17.2 17.4 21.6 17.5 −15.21 diff O8-O9V id
a
HII25 10:03:11.78 -26:09:47.3 2.6 15.7 16.6 20.8 16.6 −14.61 diff O6-O7V te
s
HII26 10:03:12.64 -26:08:52.1 6.0 15.7 15.5 19.7 15.8 −14.60 diffext O5III HII9RMc;Ho3;Hu8 a
n
HII27 10:03:12.84 -26:09:54.9 2.0 16.8 17.9 22.1 17.2 −15.05 diff O8-O9V d
H
HII28 10:03:13.32 -26:08:50.0 2.4 15.6 17.0 21.2 17.1 −14.58 diff O8V II
HII29 10:03:17.48 -26:10:00.5 6.0 16.7 16.9 21.1 17.1 −14.99 diff O7-O8V HII10RMc,Ho2 re
g
HII30 10:03:17.71 -26:09:59.4 0.8 16.0 17.5 21.7 17.6 −14.74 comp O8-O9V nearHII10RMc io
n
HII31 10:03:22.00 -26:08:53.4 2.5 15.8 17.6 21.8 17.6 −14.65 diff O8-O9V D1H6 s
in
HII32 10:03:22.92 -26:10:27.4 1.5 15.6 16.5 20.7 16.2 −14.58 −14.55 comp O7V N
HII33 10:03:25.50 -26:10:54.7 18.0 17.5 16.3 20.5 16.9 −15.33 ext O5-O6V G
C
HII34 10:03:25.80 -26:09:08.9 0.9 17.4 17.0 21.2 16.7 −15.23 −15.29 comp O7V 3
1
HII35 10:03:27.19 -26:10:22.4 19.0 17.7 17.3 21.5 17.5 −15.39 extcmplx clump Ho1,Hu1 0
9
HII36 10:03:27.90 -26:09:36.4 2.5 17.3 17.4 21.6 16.4 −15.25 diff O8-O9V
HII37 10:03:27.96 -26:09:19.9 0.9 13.6 16.7 20.9 15.2 −13.75 comp O7-O8V
HII38 10:03:28.00 -26:10:22.8 3.0 16.9 16.8 21.0 17.6 −15.09 diff O7-O8V F5H1
HII39 10:03:28.08 -26:09:14.8 3.0 17.5 17.3 21.5 17.8 −15.33 diff O8-O9V F5H2
HII40 10:03:28.51 -26:09:21.8 0.8 13.2 15.4 19.6 14.4 −13.55 −13.57 comp clump nearF5H4,H3,H5
(a)Vstellarmagnitudeoftheionizingstar,asderivedrelativetoDKIphotometry.
(b)Fluxinergcm−2s−1,column9:fromspectroscopy;column10:fromexpression(1).
(c)Nomenclature:comp:compact,cmplx:complex,diff:diffuse,ext:extended,unres:unresolved.
(d)References:RMc,Richer&McCall1992;Ho:Hodge1969;Hu:Hunteretal1993;F3H1,F5H4,D1H6,...:Bresolinetal.1993.