Wolf–Rayet central stars of planetary nebulae identified on the AAO/UKST Hα survey

12 Pages·2003·0.35 MB·English

Mon.Not.R.Astron.Soc.341,961–972(2003)
More Wolf–Rayet central stars of planetary nebulae identified
on the AAO/UKST Hα survey
(cid:3)
Q. A. Parker1,2 and D. H. Morgan3
1DepartmentofPhysics,MacquarieUniversity,NSW2109,Australia
2Anglo-AustralianObservatory,POBox296,EppingNSW1710,Australia
3InstituteforAstronomy,UniversityofEdinburgh,RoyalObservatory,BlackfordHill,EdinburghEH93HJ
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Accepted2003January28.Received2003January28;inoriginalform2002November25 o
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ABSTRACT d
ThecentralstarsofanotherfourofthenewplanetarynebulaefoundduringscansoftheAnglo- fro
m
AustralianObservatory/UKSchmidtTelescopeHαsurveyoftheMilkyWayhavebeenfound h
toexhibitWolf–Rayetemissionfeatures.One(PM4)isa[WC8]star;theotherthreeareearly- ttps
type stars of class either [WC4] or [WO4]. One of the [WC4] stars (PM3) exhibits unusual ://a
c
spectralfeaturessuchasthosefoundforPMR1byMorgan,Parker&Russeil,whichmaybe ad
e
attributed to enhanced nitrogen in its atmosphere and could be indicative of unusual stellar m
ic
evolution.ThenebulaaroundPM3hasabright,dense,high-excitationcore.Supplementary .o
u
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photometricdataareconsistentwiththeobjectsbeingplanetarynebulae. .c
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Key words: stars: chemically peculiar – stars: evolution – stars: Wolf–Rayet – planetary /m
n
nebulae:general. ra
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Acker & Stenholm 1998). Previous to our new PN survey, nitro- s
1 INTRODUCTION gen lines have rarely been seen in those central stars exhibiting trac
Thisisthesecondpaperinaseriesonthecentralstarsofplanetary WRcharacteristics.Apartfromtheonecentralstarbelongingtothe t/3
4
nebulae(PNe)identifiedontheAnglo-AustralianObservatory/UK [WN]sequencefoundintheLargeMagellanicCloud(LMC,Pen˜a 1/3
SchmidtTelescope(AAO/UKST)HαsurveyoftheMilkyWayand etal.1995)andtheweak-linedstarsthatoftenshowNIIIlinesnear /9
6
Magellanic Clouds (Parker, Phillipps & Morgan 1999). The first 4640A˚ (Tylenda,Acker&Stenholm1993),onlyPMR1andPM3 1
/1
(Morgan,Parker&Russeil2001,hereafterPaper1)describedthe showNVλ4603,19withanysignificantstrength. 00
7
spectra of the first two central stars. One – PMR1 – was seen to 1
2 PLANETARY NEBULA 5
be a [WC4] (or [WO4]) star with a remarkably strong emission 0
feature at 4605–4615 A˚ which was attributed to NV; the other – IDENTIFICATION PROCEDURE by g
PMR2–wasa[WC9–10]starthatshowedweakNIIIlines.Five The AAO/UKST narrow-band Hα survey of the Milky Way and ue
s
morecentralstarcandidates(PM3–7)havenowbeenidentifiedand MagellanicCloudsisthenewestandlastgreatUKSchmidtTele- t o
observed spectroscopically. Four are [WC] stars but one of these scope sky survey now essentially complete and available on-line n 0
againappearstopossessenhancednitrogeninitsatmosphere.These throughSuperCOSMOSscansoftheoriginalsurveyfilms(Parker 9 A
Wolf–Rayet(WR)starsandtheirassociatednebulaearedescribed 2002;andseehttp://www-wfau.roe.ac.uk/sss/halpha/).Itusedaspe- p
inthispaper.Thefifth(PM5)ishighlyunusual,notonlywithits cially designed and unusually large Hα interference filter of ex- ril 2
0
nebularspectrumshowingemissionlineswithexpansionvelocities ceptionalquality(Parker&Bland-Hawthorn1998)which,together 1
9
exceeding150kms−1,butalsowithnitrogenfeaturesintheWR withthefine-grainedTech-Panemulsionasdetector(Parker&Malin
centralstarthataresoprominentthatitsclassificationisoftheWN 1999),providesasurveyofGalacticionizedhydrogenthatisun-
classmakingituniqueintheGalaxy.Thisobjectwillbedescribed surpassedinitscombinationofdepth,resolutionandarealcover-
elsewhere and its status as a [WN] central star will be discussed age (Parker & Phillipps 1998). This Hα survey is providing the
(Morgan,Parker&Cohen2003). source material for a search for new PNe in the Southern Galac-
ThisaccumulatingsampleofnewlydiscoveredWRcentralstars tic plane, which, to date, has yielded ∼1000 PN candidates from
ofplanetarynebulae(CSPN)alreadymakesanimportantadditionto preliminaryvisualscansof80percentofthesurveyfilms(Parker
theknownpopulationofsuchstarsintheGalaxy,whichpriortoPa- etal.2003b).Theprogrammeisexpectedtomorethandoublethe
per1consistedofjust56[WC]starsaslistedbyJefferyetal.(1996). knownpopulationofGalacticPNeasrecordedbyAcker,Marcout
Therearealso34CSPNknownwithveryweakemissionlines,most &Ochsenbein(1996).TheseobjectsarenowpartoftheMacquarie/
ofwhichareprobablyofthe[WC]–PG1159class(Parthasarathy, AAO/StrasbourgCatalogueofGalacticPlanetaryNebulae,version
1.0ofwhichisavailableonCD-ROM(Parkeretal.2003a).Obvious
(cid:3)E-mail:[email protected] candidatecentralstarscanbeseeninsome((cid:1)5percent)oftheHα
(cid:4)C 2003RAS
962 Q.A.ParkerandD.H.Morgan
Table1. Detailsoftheassociatedplanetarynebulae.
PM3 PM4 PM6 PM7
RA(J2000) 16h41m04.35s 18h02m38.28s 13h36m23.05s 18h44m07.9s
Dec.(J2000) −53◦02(cid:6)24.6(cid:6)(cid:6) −14◦42(cid:6)03.5(cid:6)(cid:6) −59◦53(cid:6)24.4(cid:6)(cid:6) −12◦26(cid:6)54.0(cid:6)(cid:6)
l,b 333.47◦,−4.37◦ 14.28◦,+3.80◦ 308.55◦,+2.49◦ 21.01◦,−4.05◦
Diameter 20.5arcsec 19arcsec 13.5arcsec 13.5arcsec
Hαsurveyfilm HA17998 HA18858 HA18450 HA18508
Hαsurveyfield 291 968 180 1061
IRASsource 16371−5256 17597−1442 – 18412-1229
PNdesignation PNG333.5−04.4 PNG014.3+03.8 PNG308.5+02.5 PNG021.0−04.1
PHRPNdesignation PHR1641-5302 PHR1802-1442 PHR1336-5953 PHR1844-1226
ThePHRnomenclaturereferstotheoriginalPNedesignationgivenfortheobjectsreportedinthenewPNecataloguedescribedby D
Parkeretal.(2003a). ow
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images.Avigorousprogrammeoffollow-upspectroscopyisunder- underthesecircumstancesthatanotherfourofthenewPNewere a
d
wayonavarietyof2-mclasstelescopesforallthecandidatePNe foundtohaveWRcentralstars.Theseobjectsandassociatednebu- ed
discovered.About700havenowbeenobservedspectroscopically laearedescribedinthispaperwithdetailssummarizedinTable1, fro
and seven with central stars showing WR emission features have whiletheHαsurveyimagesoftheseWRCSPNarereproducedin m
h
beenidentifiedtodate. Fig.1.TheJ2000quotedpositionsareaccurateto1arcsecandare ttp
s
given for the central stars as determined from the on-line Super- ://a
COSMOSSkySurvey(SSS),wheretheWorldCoordinateSystem c
3 IDENTIFICATION OF THE WR a
CENTRAL STARS asderivedfromglobalastrometricFITSareincorporatedintothefits dem
headerofeachextractedimage(Hamblyetal.2001).Theprojected ic
Duringspectroscopicfollow-upofthePNcandidates,candidatecen- angularextentsofthesurroundingnebulaeweredeterminedfrom .o
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tralstarswereusuallyincludedonthespectrographslitanditwas simple microscope measurement of the original Hα survey films p.c
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Figure1. IdentificationchartsforPM3(topleft),PM4(topright),PM6(bottomleft)andPM7(bottomright)showingthesurroundingnebulae.Thecentral
starsarepositionedatthecentresoftheimages.TheimagesaretakenfromtheoriginalHαsurveydiscoveryexposures.Thedimensionsare2×2arcmin2;N
istothetopandEistotheleft.ThefaintcentralstarsofPM6and7havebeenhighlightedforclarity.
(cid:4)C 2003RAS,MNRAS341,961–972
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andareaccurateto5arcsec.AccordingtotheSIMBADdatabaseand stellarcontinuumasseenbytheMSSSOtelescopewiththoseseen
thelatestPNCatalogueSupplement(Ackeretal.1996),thereare intheequivalentcalibratedSAAOspectrum.
noknownopticallyidentifiedPNeorWRstarsatanyoftheseloca- Fig.2revealsthatthe‘stellar’imageatthecentreofthenebulais
tions,butPM3,4and7docoincidewithIRASsources.Thesourceat actuallyacombinationoftheWRcentralstarandabright,compact
PM4islistedinthePNCatalogueSupplement(Ackeretal.1996) nebularregionthatisdifferentiatedfromthediffusecircularouter
as GLMP698 solely on the basis of near-infrared photometry by nebulainthestrengthandrichnessofthenebularlinesseen.This
Garcia-Larioetal.(1997).TheHαimageandourfollow-upspec- isseenclearlyinFig.3,whichshowstheprofilesoffourimportant
troscopyconfirmsthePNwhilealsorevealingtheWRcentralstar. nebularemissionlinesobtainedperpendiculartothedispersiondi-
Aswillbeseenlater,thecentralstarwasincorrectlyidentifiedby rection:[OIII]λ4363,HeIIλ4686,Hβand[OIII]λ5007.Theseare
Garcia-Larioetal. producedfromtheMSSSOspectrumaftersubtractionofanequiv-
alentnearbyoff-lineprofiletoeliminatethecontributiontotheline
profilefromthecentralstaritself.Theprofileisleastreliablefor
4 SPECTROSCOPIC OBSERVATIONS
HeIIλ4686becausetheneighbouringstellarcontributionchanges D
Spectra of the central stars of PM3, 6 and 7 together with their rapidly with wavelength owing to the many WR broad emission ow
associatedexternalnebulaewereobtainedwiththeSouthAfrican linesthere.Theshapeoftheouternebulaisbestseeninthe[OIII] nlo
AstronomicalObservatory(SAAO)1.9-mtelescope:PM3on2000 λ5007line,thoughitisalsoevidentintheHeIIλ4686andHβlines. ad
e
Jinusnteru2m0e,nPtaMls6etounpo2n00e1acMhaoycc1a7sioanndwPasMes7seonnti2al0l0y1asMdaeysc2ri1b.eTdhine Tcohmepfoarremswsuigthgtehsetsmaonreanunnuifloarrmmnoerpbhuolalrodgiyscinse[eOnIiInI]thλe50H0α7swurhvicehy d fro
m
Paper1,whichgaveaspectralrangeof3800–7300A˚ ataresolution imageinFig.1. h
of3A˚ pixel−1.Theintegrationtimeswere900,1800and1200s, ThetopspectrumofFig.2(PM3centre)wasobtainedbyextract- ttp
s
respectively,andtheslitwidthwas400µmor2.5arcsec. ingthosepixelsbetweenthetwominimaofthe[OIII]λ5007line ://a
SpectraofthecentralstarsandassociatednebulaeofPM3,4and seeninFig.3.Thelinesthereclearlyincludeacontributionfromthe ca
6 were observed at Siding Spring Observatory using the Double outernebula,butthisisonlysignificantfor[OIII]λ5007and[OIII] dem
BeamSpectrograph(DBS)ontheMSSSO2.3-mtelescope:PM3 λ4959.Thespectrumoftheouternebula(position2)wasextracted ic
.o
on2000July2,PM4on2000July1andPM6on2001June24and frompixelsonthebrighterwingoutsidetheappropriateminimum. u
p
26.Again,theinstrumentalsetuponeachoccasionwasasdescribed TheredpartofthePNspectrumisdominatedbyHα.Linesother .c
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inPaper1,andgavehigh-resolution(∼1A˚)redspectraintherange thanHαarenoteasilydiscernedabovethenoiseintheredspectra m
6085–7050A˚ usinggrating1200Randmedium-dispersion(2.2-A˚ oftheouterpartsofthenebula.Lowionizationlinesareweakor /m
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resolution) blue spectra in the range 4050–5960 A˚ using grating absent: [NII] λ6584 is extremely weak at 0.2 per cent of Hα in ras
600V.A2-arcsecslitwasemployedandtheintegrationtimeswere the compact central zone and ∼1 per cent of Hα in the diffuse /a
1200,1800and1200s,respectively. outerregion;the[SII]λλ6717,6731linesarenotseen.TheSAAO rticle
The IRAF package was used to reduce and analyse the spectra spectrumisstrongenoughtoshowtheargonlinesaround7200A˚ -a
b
fooblsloerwviendgasttabnodthardSAprAoOcedanudreMs.SNSoSteOt.hRateolantliyvePsMpe3catrnodpPhoMto6mweetrrye athnedrpedroavniddebsluaeg(onoodn-moveearsluarpepoinfgH)earImλs58o7f6th,ewDhiBcShsfaplelcstrboegtwraepehn. strac
waspossiblefortheSAAOdatathroughhavingusedawideslitin Overall,itmatcheswellwiththeMSSSOspectrum. t/3
4
goodseeingconditionsandwasachievedthroughobservationsof Table2providesalistofthePNlinesseeninthecentralcompact 1/3
selectedstandardstars(Stone&Baldwin1983). nebula,normalizedtoHβ=100.0,fromthecombinedMSSSOand /9
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SAAOdata.TheMSSSOdatawerecalibratedfromtheSAAOdata 1/1
asmentionedearlier.Mostoftheselinesaretooweaktobeseenin 00
5 SPECTRA OF THE PLANETARY NEBULAE thefainterouternebula.TheNIIIlinesat4634and4642A˚ (multiplet 715
Thespectraofthenebulaeextractedfromaroundthecentralstarsare 2)areasnarrowastheothernebularlines. 0 b
showntogetherinFig.2.Thesourceofeachspectrumwaschosen ThecentralPNemissionspectrumisstrongandrichenoughto y g
togivethebestillustrationofthespectralfeatures.Theupperthree allowtheestimationofseveralbasicnebularparameterssuchasex- ue
spectra are mostly from MSSSO and the lower two from SAAO. citationclass(p).TheHeIIλ4686toHβlineratioisusedforhigher st o
However,theredportionofthesecondspectrum(PM3centre)is (p(cid:2)5)excitationclassmeasurements(Dopita&Meatheringham n 0
fromtheSAAObecauseitshowsextralinesfurtherintothered.The 1990).Theselinesarestrongatbothpositionsontheslitenabling 9 A
gapsseennearthecentresoftheupperthreespectraoccurbecause twoestimatesforthesedifferentzonestobemade.Surprisingly,p p
the chosen grating settings did not give any wavelength overlap wasfoundtobe6.2and8.1forthecompactandouternebularzones, ril 2
0
betweentheredandbluearmsoftheDBSspectrograph. respectively,sothattheouternebulaappearstobemorehighlyion- 1
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izedthanthecompactinnerzone.Contributionsfromtheoutershell
arenegligiblefortheselines(seeFig.3).Eventhoughsubtracting
5.1 ThenebulaaroundPM3
thestellarcontinuumfromtheobservedspectrumatposition1is
Fig.1(topleft)showsPM3asabrightcentralstarsurroundedbya noteasyforHeIIλ4686,itcanbenotedthaterrorsinthisprocedure
relativelyuniformfaintcircularnebulawithadistinctedgebutwith couldnothaveproducedthenoteddifferenceintheexcitationlevels
noobviousbrighteningatitsouterrim. inthetwozonesofthesystem;theratioHeIIλ4686/Hβwouldstill
Thenebularspectrumitselfisextremelyrichandvariesacrossthe bebelowthelevelseenintheouterzoneevenifnostellarcontinuum
faceofthenebulaasprojectedontheslit.ItisshowninFig.2fortwo hadbeensubtracted.
positionsalongtheslit:(i)acrossthecentralstar,toppaneland(ii)on TheratioHeIλ6678/Hαisfoundtobethesameforeachzone,
theouterrimtotheeastofthecentralstar,secondpanel.Theformer so the higher level of HeII λ4686 (relative to hydrogen) seen in
showstheresultaftersubtractionoftheunderlyingstellarspectrum. theouterzoneisnotcausedbyahigherheliumabundancethere.
NodirectcalibrationwasavailablefortheseMSSSOspectrasoa Themostprobableexplanationforthisunexpectedsituationisthe
simplecalibrationwasappliedaftercomparingthebrightlinesand presence of localized pockets of high-density material within the
(cid:4)C 2003RAS,MNRAS341,961–972
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Figure2. Spectraofthenebulae.Thespectra(allexceptforPM4)arecalibrated,buttheintensityscaleisarbitraryandwaschosenforillustrativepurposes g
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only.Furtherdetailsoftheplottedspectraaregiveninthetext. e
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innerzone.Anotherexplanationisthatthestarcooledrapidlyjust sitytheremustbehigh,i.e.logn (cid:2)6.AvalueoflogT ∼4.0is 09
b(Peefon˜raeettheals.p1e9c9tr7a)l,obbustetrhviastiiosnusnwliekreelymbaedcea,uassedtihdeNli6g6hitntrtahveeLltMimCe taipopnriospprioastseibaltehaigtihndteernmsietdieiastoefdleonegsintiee∼s(l8o–g1n0e,∼but6–n8o)u.nTiehqeuleascoklouf- April 2
totheouterrimisonly0.8yrfora0.5-pcdiameterPN. anobviousextendedregionaroundthecentral[OIII]λ4363profile 01
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Forbothzonesofthenebula,[OIII]λ4363isapproximatelyequal inFig.3showsthatthislineismuchweakerintheouternebula.
instrengthtoHγ andsufficientlystrongtoallowagoodmeasure- Therefore,thebestresultfortheouternebulaisobtaineddirectly
mentofthe[OIII]lineratio(λ5007+λ4959)/λ4363,therebypro- fromthespectrumthere.Themeasuredlineratioof39allowslog
vidinganestimateoftheelectrontemperature(T ).However,inthe T ∼4.3atlowdensitiesfallingtologT ∼3.7athighdensities.
e e e
innerzone,[OIII]λ4363issostrongwithrespectto[OIII]λ5007 The high-resolution red spectrum obtained at MSSSO with
thatthelineratiomustbeaffectedbytheelectrondensity(n )and G1200Risgoodenoughtoallowanestimateoftheexpansionveloc-
e
so cannot provide a unique value for T . Since the λλ5007,4959 ity,v ,seeninthecentralzone,althoughonlyHαisstrongenough
e exp
lines in the central nebula include a significant contribution from tobemeasuredwithanyreliability;itsFWHMis32percentgreater
theouterregion,itisbesttomeasurethe[OIII]linesusingtheneb- thanthatoftheskylines(whichcanbeusedasameasureofthe
ular profiles of Fig. 3 and to separate the contributions from the instrumentalprofile).AftersubtractingtheFWHMoftheskylines
outerandcentralpartsofthenebulabyinterpolation.Theresulting inquadrature,v ,takenashalftheFWHM,is25kms−1 which
exp
(λ5007+λ4959)/λ4363ratioforthecentralzoneisthen3.2.Using isalevelcommonlyfoundinPNewith[WC4]centralstars(Pen˜a,
thecalculationsofLynch&Kafatos(1991),itisclearthattheden- Stasinska&Medina2001).
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Figure3. ProfilesofthePM3systeminfouremissionlinesperpendicular Figure4. ProfilesofthePM4and6systemsinvariousemissionlines.The ://a
tothedispersiondirection.ThedataarefromtheMSSSO2.3-mtelescope dataarefromtheMSSSO2.3-mtelescopeandoff-linesubtractionhasbeen c
a
andoff-linesubtractionhasbeenapplied. applied. d
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Table2. NebularemissionlinesinPM3(centre). OnlyMSSSODBSspectraareavailable.Fig.4showstheprofiles .o
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ofthenebula,perpendiculartothedispersiondirection,forthe[OIII] p
Line(A˚) Int Note Line(A˚) Int Note λ5007,Hαand[NII]λ6584linesaftersubtractionofnearbyoff-line .com
continuumprofiles.Theredlinesshowthenebulatobeflat-topped /m
HHII44130410 1209 11 HHeeIII55847132 362 12 as from a uniform disc, but the [OIII] λ5007 profile has a clear nra
[OIII]4363 41 1 [OI]6300 2 1 narrowcentralcoreofapproximatelyhalfthediameterofthefull s/a
HeI4471 4 1 [SIII]6312 2 1 nebula. rtic
HNeIIIII44653442 11 11 [[AOIV]]66346335 14 11 areTphleocttoemdbininFeidg.b2lu(ethainrddrpeadnDelB).SOsnpleyct[rOafIIoI]rtλhλe5b0r0ig7h,4tc9e5n9traanldzoHnβe le-abs
NIII4641 2 1 HI6563 796 1 (weak)aredetectedintheblueandHα and[NII]λλ6548,6584in tra
HeII4686 34 1,3 NII6584 1 1 the red. The spectra are not calibrated, but the ratios of the lines ct/3
[AIV]4712 5 1 HeI6678 11 1 withineachtriowouldchangeverylittleifthecalibrationcurves 41
[[ANeIVIV]]44774205 27 11 H[AeVI]70760506 1442 22 λus6e5d84fo/HrαPMis∼30(s.6amaneddtehteecottohresr)lwineerreataipopsliimedp.lyThaneelixnceitraattiioon[cNlaIsIs] /3/96
HI4861 100 1 [AIV]7171 7 2 of p∼4±1. 1/1
[[OOIIIIII]]45905097 14207 11,,44 [[AAIIVV]]77223683 35 22 The[NII]λ6584andHα linesinthecentralpartofthenebula, 0071
thoughweak,arebothconsiderablybroaderthantheskylinesand 5
HeI5015 2 1 0
yieldanexpansionvelocityofv =43kms−1.Thisislargerthan b
Notes: othervelocitiesassociatedwithe[xWp C8]starsbutisseenassociated y g
1,MSSSOdatascaledtomatchtheSAAOdata. withsomeearlier[WC]stars(Pen˜aetal.2001). ues
2,SAAOdata. t o
3, Difficult to distinguish precise boundary between nebular and stellar n
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emission. 5.3 ThenebulaaroundPM6 9
4,Upto30percentcouldcomefromtheouternebula. Ap
Fsliigg.h1tl(ybeoltltiopmticlaelftf)aisnhtonwesbPulMa(6b/aasa∼fa0i.n8t)swtairthcolousteatnoythdeisctienncttreouotfear ril 20
Thenebularemissionfromthesmalldensecentralzoneisalso 1
rim.Thenebulaitselfistypicalofthesmalllowsurfacebrightness 9
strongenoughfortheretobeasignificantcontributiontotheob- PNcandidatesdiscoveredontheAAO/UKSTHαsurvey.OnlyHα
servedcontinuum.Usingemissioncoefficientsforagasat104Kas and[OIII]λλ5007,4959arevisibleintheSAAOnebularspectrum.
tabulatedbyOsterbrock(1974),assumingheliumtohaveanabun- Theforbiddenlinesarestrongenoughtoimplythat p (cid:2)4.[NII]
danceof0.1andafractionalionizationof0.34asdeterminedfrom λ6584 is not seen. The higher dispersion MSSSO red spectrum
therelativestrengthsofHeIλ4471andHeIIλ4686,andneglect- showsonlyHα,theprofileofwhich,perpendiculartothedispersion
ingtwo-photonemissiononaccountofthehighelectrondensity,
directionandwithasuitableoff-linecontinuumprofilesubtracted,is
thecontributionfromthegastothetotalcontinuumiscalculatedto showninFig.4.Again[NII]λ6584isnotseenandis(cid:1)0.1Hα.The
varyfrom23percentatHβto34percentatHα. Hαlineisbroaderthantheskylinesandyieldsv =38kms−1.
exp
5.2 ThenebulaaroundPM4 5.4 ThenebulaaroundPM7
Fig.1(upperright)showsPM4asastarclosetothecentreofa Fig.1(bottomright)showsanearlycircularnebulawithnodistinct
nearlycircularnebulawithanenhancedouterrimtothenorthwest. outerrim.Thecentralstarisfaintandthereisanadjacentbrighter
(cid:4)C 2003RAS,MNRAS341,961–972
966 Q.A.ParkerandD.H.Morgan
starapproximately2.5arcsectothenortheast.OnlySAAOspec-
6 SPECTRA OF THE NEWLY IDENTIFIED
tralobservationsareavailableforPM7andthecentralstar,which
WR CENTRAL STARS
couldeasilyhaveincludedlightfromtheadjacentstartoo.Thecali-
bratedspectrumisshowninFig.2.OnlyHαand[OIII]λλ5007,4959 ThenormalizedspectraofthenewlyidentifiedWRcentralstarsare
arevisibleinthenebularspectrum.Againtheforbiddenlinesare shownasamontageinFig.5withthemajoremissionlinesmarked,
strong enough to imply that p (cid:2) 4. [NII] λ6584 is not seen and theidentificationstakenfromMoore(1959,1970)and,inthefar
is(cid:1)0.2Hα.Thereisnohigh-dispersionspectrumfromwhichto red,fromVreux,Dennefeld&Andrillat(1983)andConti,Massey
extract a good profile of the nebula or determine an expansion &Vreux(1990).ThemontageincludesthespectraofPMR1and2
velocity. takenfromPaper1,forcomparisonpurposes.ThespectraofPM6
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Figure5. NormalizedspectraofthenewcentralstarsPM3,4,6and7withthoseofPMR1and2shownforcomparison.Theimportantemissionlinesare
marked.
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MoreWolf–Rayetcentralstars 967
Table3. WRemissionlinesinthecentralstarPM3. the prevalence of such nitrogen enrichment in many of the seven
WRCSPNdiscoveredsofarmayindicatethatcandidateselection
Line(A˚) Wλ(A˚) FWHM(A˚) Note from the AAO/UKST Hα survey is sensitive to an unusual strain
ofstellarevolution(andthe[WN]candidate–nitrogenisstrongly
NV4607 86 34
CIV4654 91 25 presentintwooutoffourearly[WC]starsandweaklypresentin
HeII4686 66 24 1 oneorbothofthelate[WC]stars).
HeII4861 – – 2 ItisworthcomparingsomelineratiosbetweenPMR1andPM3,
OVI5290 17 20 which are of the same spectral class. The ratios of the three CIV
HeII5412 – – 2 lines at 4658, 5471 and 5808 A˚ are approximately 6 : 1: 11 in
CIV5471 25 21 PM3and7:1:58inPMR1,i.e.CIVλ5808changesinstrength
OV5590 80 38 dramaticallyfromstartostarwithrespecttoboththeotherCIVlines.
CIV5808 180 30 4
ThisisnotunlikethesituationinWNstars,whichoftenhaveCIV
CHeIVII76752660 125430 6431 13,4 5λ4578108A˚baurtenroecootmhebrinCatIiVonlinliensesinsothtehierisrpceocmtrpaa.rHatoivweevinetre,n4s6it5ie8saanrde Dow
Notes: anticipatedtobesimilar,whereasthe5808-A˚ CIVlineisstrongly nlo
1,Difficulttodistinguishbetweennebularandstellarcomponents. a
affectedbyvariationsintemperatureandopticaldepthsothelarge d
2,Nomeasurementbecauseofrelativelystrongnebularlines. e
observedrangeisnotaltogetherunexpected(Hillier&Miller1999). d
3sp,eHcitgruhme.rrorcausedbyuncertaincontinuumclosetotheendofthe Incontrast,theratiosoflinesofotherelementstoCIVλ4658and from
4,FromSAAOspectrum(remainderarefromMSSSOspectra). CIVλ5471changelessbetweenPM3andPMR1:OVIλ5290and h
OV λ5590 are comparable in the two stars, NV λλ4604,4620 is ttps
strongerbyafactorof2inPM3andHeIIisweakerbyafactorof ://a
and7arefromSAAOdataandthatforPM4isfromMSSSOdata. 2inPM3. ca
d
ForPM3,mostofthespectrumisfromMSSSOdata,butthepart AswithPMR1,noothernitrogenlinesareseen:thestrongNIV em
between5730and6070A˚ isfromSAAOdata.Thenarrownebular λ7113 line is absent, as it is from the earliest WN stars, and NV ic
emissionlinesshowninFig.2havebeenremoved. λ4744wouldnotbestrongenoughtobeseenagainstthebackground .ou
p
noise. .c
o
However,whereastheemissionlineswereverystronginPMR1, m
6.1 TheWRstarPM3 /m
theyaremuchweakerinPM3,evenafteradjustmentforthenebular
n
TheWRemissionlinesseeninPM3arelistedinTable3together continuum.TheequivalentwidthofCIVλ5808issmallerthanin ras
watihthalmfemaasxuirmemumenthseoigfhthte(FirWeqHuMiva).leTnhtewseidmthesa(sWurλe)maenndtsfualrlewbiadstehds masossmtoafllthaes[iWn tCh4e][sWtaCrs3l]isstteadrsb;ybTuytlietnsdFaWetHaMl.(i1s99sm3)a,ltlheoruthgahnnoint /artic
le
ontheobservedcontinuum;takingintoaccountthecontributionto bothclassesandalmostatthelevelseenintheweak-linedcentral -a
b
bthyebceotnwteineunu3m3farnodm5t0hpeenrecbeunlta.rgaswouldincreasetheWλvalues isttairssu.nHliokweleyvethr,atthPeMse3haisveavPeorpyumlauticohnwIestaakrebrelcinaeusse(WPoλp)u.lHateinocneI, strac
ThespectrumshowsthelinesofCIV,OVandOVIthatarechar- WC4starshavemuchstrongerlines(Smithetal.1990). t/34
acteristicofanearly[WC]star.Inthisrespect,PM3issimilarto 1/3
PMR1,althoughCIVλ5808isverymuchstrongerinthatstar.CIII 6.2 TheWRstarPM4 /96
λ5696isnotseenineitherspectrum,butCIVλ5808inPM3isnot 1/1
strong enough to allow this non-detection to distinguish between OnlyMSSSODBSspectraareavailableforPM4.Detailsofsomeof 00
7
[WC5] and hotter classes. As with PMR1 (Paper 1), the precise theimportantWRemissionlinesseenarelistedinTable4.Theim- 1
5
subclassisdifficulttodetermineaccordingtotherecentclassifica- portantfeaturesare:CIIIλλ5696,4650areverystrong,CIVλ5808is 0 b
tionschemesofKingsburgh,Barlow&Storey(1995)andCrowther, strongbutmuchweaker,andCIIλ4267isveryweak.CIVisalsoseen y g
deMarco&Barlow(1998)becausethesearebasedontheOVI3818 at4441and5471A˚,andCIIisseenat5132A˚.Usingthesubclass ue
s
line,whichisnotincludedinthepresentspectra.However,older definitionsofCrowtheretal.(1998)toclassifyPM4,theappropri- t o
schemescanbeused:thelineratioOVIλ5290/OVλ5590givesa atelineratios[log(W5808/W5696)=−0.1,andlog(W5808/W4267= n 0
classof[WC4]orlater(Mendez&Niemela1982),andthelineratio 1.1)]bothgivePM4as[WC8].However,CIVλ5808issocloseto 9 A
CapIpIIroλp5r6ia9t6e/OforVthλe55[W90C,5w]hcilcahssis(Scmleiatrhl,ySfhaarrfar&omMtohfefavta1lu9e90o)f,guinvietys tNheeveenrtdheolfesths,ethMeS[SWSCO8s]pcelcatsrsuimficathtiaotnitisissulepspsorretelidabblyeathtahnirudsluianle. pril 2
0
[WC4]orearlier.Hence,[WC4]isthebestclassification.However, ratio[log(W /W )=1.2],whichisappropriatefora[WC8] 1
5696 5592 9
as discussed in Paper 1 for PMR1, [WO4] might be appropriate star(Torres,Conti&Massey1986).
becausebothCIIIλ5696andCIIIλ6742areweakorabsent. TheDBSredspectrumshowstwostronglines:CIIλ6580(includ-
PMR1 is unusual in that it has a strong line at 4610 A˚ in the ingHeIIλ6560)andCIIIλ6740(includingCIIλ6740),plusweaker
shoulderoftheblendedCIVλ4658–HeIIλ4686emissioncomplex, linesofHeIIλ6678andCIIλ6784.Thesearealsoconsistentwith
whichwasattributedinPaper1toNVλλ4604,4620.Fig.5shows theclassof[WC8](Vreuxetal.1983).
that this line is also present in PM3 and is even more extreme IntheassociatedDBSbluespectrum,adistinctemissionfeature
withCIVλ4658–HeIIλ4686andNVλλ4604,4620atcomparable canbeseenshortwardofCIIIλ4650,almostasstrongasHeIIλ4686.
strength.ThepresenceofsuchstrongNVfeaturesinthissmallbut AsimilarfeaturewasnotedinPMR2,but,whereasinthatstarit
significantnewsampleofWRCSPNisasurprisegivenitsrarity is a close pair of lines coincident with NIII λ4634,4641, in PM4
inexistingcatalogues.WithsuchanapparentstrongNVinPM3 itappearstobesingleandat4634A˚.ItwasattributedinPMR2
wesuggestafinalclassificationas[WC4pec],whichinretrospect toNIIIbecauseoftheaddedpresenceofapairoflinesthatfitted
mightalsobeanappropriateclassificationforPMR1.Coupledwith NIIIλ4097,4103(regionnotshowninFig.5).Itisdifficulttotell
thediscoveryofaprobable[WN]star(PM5,Morganetal.2003), with certainty whether these lines are seen in PM4 because the
(cid:4)C 2003RAS,MNRAS341,961–972
968 Q.A.ParkerandD.H.Morgan
Table4. StellaremissionlinesinPM4. Table5. WRemissionlinesinthecentralstarPM6.
Line(A˚) Wλ(A˚) FWHM(A˚) Note Line(A˚) Wλ(A˚) FWHM(A˚) Note
CII4267 6 – CIV4658 178 61 1,4
CIII4326 11 – OV5590 (37) 64 2
CIII4516 8 10 CIV5808 1300 37
NIII4634 13 10 HeII6560 (53) 65 3
CIII4650 136 11 1 CIV7061 35 28
HeII4686 19 10 CIV7726 (174) 34 4,5
HeII5411 5 7
Notes:
CIV5471 5 7
OIII5592 (cid:1)3 – 2 1W,λFuinllpbalerenndth4e6s2e3s–a4r7e0h7igA˚h;lyinucnlucdeertsaiHne. iiλ4686.
CIII5696 91 13
2,Weakline.
CIV5808 75 – 3,4 3,RemovalofnebularHαuncertain. Do
CII6580 41 36 5 w
4,Weakcontinuumlevel. n
HeII6679 5 – lo
4,ClosetoedgeofCCD. a
CIII6740 31 25 de
CNoIIte6s7:84 11 – goodenoughtoshowthatthereisnoevidenceofNVλλ4604,4620 d from
21,,ABlfefencdteodfCbyIInIiagnhdtCskyivl.ine. eamstihsasitosneeinnitnhePMwiRng1oafndthPeMC3IV.Tλh4e6s5t8ru+cHtuereIIsλe4en68i6ntbhleenbdle,nsducaht https
3,IncludesbothCIVlines. 4658A˚ couldbecausedbynoise.Adeeperspectrumofthestaris ://a
54,,IEnncdluodfesspHecetIrIuλm65–6u0nlcienretsa.incontinuum. ntheeed4e6d58toA˚esctoamblpislhext.hTehcelalsisniefiscaartieolnisatendditnoTcaobnlfier5metvheenstthruocutguhrethoef cadem
errorsofmostarehigh. ic.o
u
spectrum is rather noisy there. Alternative identifications for the p.c
lineat4634A˚ areOIImultiplet1andSiIVmultiplet6.However, 6.4 TheWRstarPM7 om
thesearelessprobablebecausetheformeroccursat4642A˚ rather /m
than4634A˚ andthelinesofOIIat4415and4593A˚ whichareseen PM7 is also an early [WC] star but the spectrum is weaker still. nra
clearlyinPMR2arenotdetectedinPMR4;theSiIVline,though AllthatcanbeseenisCIVλ5808with Wλ =160andFWHM= s/a
at4631A˚,isnotmatchedbylinesat4088,4116and6701A˚.No 44A˚.Thestarisprobably[WC4]orthereabouts.Theunnormalized rtic
line is seen at 4634A˚ in the [WC8] stars NGC 40 (Leuenhagen, spectrumisveryred,thusexplainingthelackoflinesintheblue. le-a
Hamann&Jeffery1996)andHe2-459andM2-43(Leuenhagen& This is probably caused by the close companion seen in Fig. 1. bs
Hamann1998)(thoughCrowtheretal.(1998)classifiedHe2-459 There appears to be a weak TiO absorption band near 6200 A˚, tra
c
as[WC9]anddidnotobservetheother). whichprobablyarisesfromthisneighbouringstar.NaDisalsoseen t/3
The WR lines visible in PM4 are not particularly strong with inabsorptionfromeitherinterstellargasorthecompanionstar,in 41
CIIIλ5696havingWλ=91andFWHM=13A˚,whichareweaker whichcasethecompanionisprobablyaK7–M0Vstar.Thepresence /3/9
t2h8anA˚,threespmeecatisvuerleym)eanntdssfeovretrhaelb[uWtCno8t]asltlatrhNeG[WCC490]s(taatrs14q0uoatnedd foafctthoerocfom2poarn3i.oninthespectrumcouldhavereduced W5808 bya 61/10
0
byCrowtheretal.(1998).PopulationIWC8starshaveevenstronger As for PM6, a deeper spectra would be helpful to clarify the 71
=lin5e7s.5FaonrdeFxWamHpMle,=va3l6ueA˚sftaokreCnIIfIroλm56S96m.iAthlseottahle.(F1W99H0M)gfioverCWIIλI spectraltypeofPM7. 50 by
λ4650is26A˚ comparedwith10A˚ foundforPM4). gu
7 THE NATURE OF THE WR CENTRAL STARS e
s
t o
Thissectionincludesdescriptionsoftheavailablephotometricdata n
6.3 TheWRstarPM6 0
forthenewPNeandtheircentralstars.Calculatedparameterssuch 9
A
PM6issimilartoPMR1inthatitisanearly-type[WC]starac- as distance and diameter are presented in a summary table near p
cordingtotheSAAOspectrumobtained.Althoughaspectrumof the end of the paper. It is well known that it can sometimes be ril 2
0
the surrounding faint nebula was also taken at MSSSO, the faint difficult to distinguish [WR] CSPN from Population I stars with 1
9
WRcentralstarwasnotlocatedontheslit.TheSAAOspectrum surroundingringnebulae.Herewebringtogetherthevariousstrands
ofPM6hasverystrongCIVλ5808emissionwithWλ=1300and ofevidenceanddatacurrentlyavailabletosupportthenatureofthis
FWHM=37A˚.OVλ5592canbeseen,butCIIIλ5696andtheother sampleasWRCSPNincludingconstraintsimposedbyconsidering
linesinthegreencannotbedistinguishedfromthenoise.Theclass thelocationsoftheseobjectswithintheGalaxy.
is probably [WC4] or earlier. CIV λ7061 is clearly seen but CIII
λ6742isnotdiscernibleabovethenoiseandcannotbemorethan
7.1 Locationalconstraints
halfthestrengthofCIVλ7061.TheCIIIlineisusuallygreaterthan
orequaltotheCIVlineinWC4–5stars,soPM6isperhapsear- AccordingtotheseventhCatalogueofGalacticWolf–RayetStars
lier. As discussed in Paper 1 for PMR1 and above for PM3, the (vanderHucht2001),PopulationIWCstarsareconfinedinheight
spectral class could be [WO4] rather than [WC4]; but, for PM6, abovetheGalacticPlanetotherangeof250–300pc.Thisimmedi-
thehighernoiselevelsweakentheargumentsomewhat.Otherlines atelyplacesupperlimitsonthedistancestothestarsdiscussedhere
seen are CIV λ5865 and CIV λ7726 (off the edge of the plotted underthehypothesisthattheybelongtoPopulationI.Theselimits
regioninFig.5).Althoughthespectrumisnoisyintheblue,itis are3.9,3.8,5.8and4.2kpcforPM3,4,6and7,respectively.They,
(cid:4)C 2003RAS,MNRAS341,961–972
MoreWolf–Rayetcentralstars 969
inturn,generateupperlimitsonthephysicaldiametersoftheneb- opticalphotometricmagnitudesinTable6arethusaveragesofthe
ulaeat0.39,0.35,0.38and0.27pc.TypicalPopulationIWRring SSSandGSCIIdatawhenmorethanonevalueinthesameband
nebulaehavediametersintherange10–50pc(vanderHucht1992), isavailable.
althoughsomewithsmaller1–3pcdiametersareknown(Marston TheaforementionedclosecompaniontoPM7isredanddomi-
1997).Eventhelowestofthesevaluesissignificantlygreaterthan natestheRandI SSSdatawheretheclosestellarpaircannotbe
theupperlimitsofthediametersdeducedaboveunderthesuppo- satisfactorilydeblended.However,the[WC]staristhebrighterof
sitionthatPM3–7arePopulationIstars.This,therefore,supports thetwointheblueandareasonableestimateofitsmagnitudecanbe
theviewthatalltheWRstarsofTable1areCSPN. madebycomparingitscountlevelsseenontheB surveywiththe
J
levelsseeninsimilarbutunblendednearbystarswithmagnitudes
availablefromtheSSS.ThisestimateisalsogiveninTable6.The
7.2 Opticalphotometricobservations
redstaristoobrighttoallowasimilarestimatetobemadeintheR
The SAAO spectra were obtained on nights of good seeing orIbands.TheotherentriesinTable6forPM7applytotheblend
((cid:1)1arcsec)throughawide(2.4-arcsecslit)andaresuitableforpro- andaregiveninbrackets. D
vidingabsolutefluxes.Afteraccountingforatmosphericextinction, Unlikethespectrophotometricdata,thebroad-banddataalsoin- ow
theywerecalibratedusingobservationsofthespectrophotometric cludecontributionsfromthevariousWRemissionlinesand,inthe nlo
a
standards LTT9239 (PM3) and LTT4364 (PM6 and 7) (Stone & caseofPM3,fromthenebularemissionlinesthatarisefromthe d
e
Bmaalgdnwitiund1e9s8a3t).51M6e0asaunrdem60e0n0tsAo˚f,t[htheemvoannodchrrobmanadtisco(cfotnhteinSumumith) dtheenseem,iusnsiroensollivneeds,wceenretrtaylpriecgailolynoansewoerllt.wTohetecnothrrseocftiaonmsaogwniintugdteo, d fro
m
(1968) system] adapted to the Hayes & Latham (1975) calibra- exceptforPM3forwhichtheywere0.9maginBJand1.6maginR. h
tion of Vega, are given in Table 6. The signal in the b-waveband Hence,VandRgreatlyexceedvandrforPM3.Sincetheintrinsic ttp
s
(4270A˚)istooweakinallofthesestarstoallowareliablemea- coloursofWRstarsarebestknowninthemonochromaticvandr ://a
surement. These data are only useful for PM3 and 6 because no bands,estimatesofv andrweremadefromthebroad-bandmea- ca
d
spectrophotometricdataareavailableforPM4andthespectrumof surementsaftersubtractingestimatesforthecontributionsfromthe e
m
PM7isbadlyaffectedbyaredcompanion.Themeasurementsfor emissionlinesusingzero-pointsfromBessell(1979)andasimple ic
.o
PM7giveninTable6arethereforeupperlimitsandaregivenin interpolation. u
p
parentheses. .c
o
Broad-bandphotometricmeasurementsforthecentralstarsare m
7.3 Availableinfraredphotometry /m
alsoquotedinTable6.ThesewereobtainedfromthevariousUKST n
SouthernandEquatorialSkySurveymaterials(Morganetal.1992) InfraredphotometryisalsoavailableformanyoftheWRstarsvia ras
u2s0i0n1g)tahnedothne-lHinuebSbulepeSrpCaOceSTMelOesScoSpkey(SHuSrTve)yGduaidtaeS(HtaarmCbaltyaleotgaule. aocfctehsesPtoNethiesIwRiAthSi,nMthSeXaarenadc2o-vMeAreSdSbyont-hleinDeEsuNrIvSeySduarvtae.yNFoirnset /article
GSC II (McLean et al. 2000). Where possible the SSS measure- Release. -a
b
ments (http://www-wfau.roe.ac.uk/sss/) were calibrated with se- stra
quencesfromtheHSTGuideStarPhotometricCatalogueGSPC2.1 c
(Bucciarellietal.2001).InsomeinstancesSSSdataareavailable 7.3.1 Near-infrared2-MASSJHKphotometry t/34
fromtwoseparatesurveyfieldsinthesamebroad-bandcolour.The StarsPM4and7fallwithintheareacoveredbythe2-MASSSur- 1/3
vey Second Incremental Release; the measurements obtained are /9
6
Table6. Photometryofthesystems. quoted in Table 6 (Skrutskie et al. 1997). In the case of PM4, 1/1
thereareerroneousdataintheliteraturepertainingtotheproposed 00
7
Object PM3 PM4 PM6 PM7 PN and its central star. The JHK photometry associated with the 1
5
v 18.8 – 20.1 (18.9) sourceIRAS17597–5256(seeTable1)byGarcia-Larioetal.(1997) 0 b
r 18.0 – 18.1 (18.0) andgiventhePNidentificationGLMP698matchesalmostexactly y g
BJ 17.3 17.5 20.3 18.4∗ 2-MASSdataforamuchbrighterstarapproximately20arcsectothe ues
V 16.8 16.5 – (17.5) westofthecentralWRstarofPM4andnotthecentralstaritself. t o
R 16.1 15.7 18.9 (16.5) This misidentification probably reflects the large IRAS positional n 0
I 16.6 – 18.2 – uncertainties.TheambiguityisresolvedeasilyherebecausePM4, 9 A
J – 13.81 – 14.32 whichiscentraltothePNasseenontheHαsurveyimage,matches p
H – 13.13 – 13.45 adetectioninthepositionallyaccurateMSXsurveywithfluxesthat ril 2
K – 12.76 – 13.30 matchtheIRASdata,andisalsocoincidentwithadifferentstarin 01
9
F(8µm) – 0.24 – –
the2-MASSsurvey.TheJHK photometryadoptedforPM4from
F(12µm) – 1.79 – –
2-MASSandquotedinTable6isthatpertainingtothecentralstar
F(15µm) – 4.30 – –
positionofthePNasrecordedinTable1.
F(21µm) – 11.61 – –
F(12µm) <0.29 1.84 – <0.28 ThepositionofPM4inthe(J−H)−(H−K)diagramisclose
F(25µm) 0.43 15.09 – <0.32 tothecoolendofthesequenceofMdwarfstarsratherthannearthe
F(60µm) 0.95: 15.78 – 1.93 mainbodyofPNe(Garcia-Larioetal.1997).However,PNewith
F(100µm) <33.08 <61.60 – 10.94: WRcentralstarsarescatteredwidelyonthisplot(Gornyetal.2001)
asaresultofthepresenceofaredline-of-sightcompanionorasa
Notes:
v,r:fromspectra. resultofthecentralstarbeingabinarysystemorbeingsufficiently
BJ,V,R,I:averagesfromSSSandGSCII. brightandcoolastodominatethenear-infraredemission.Inspection
Infraredfluxes:upper4–MSX;lower4–IRAS. ofFig.1showsthatPM4hasaclosecompanionjusttotheNNE.
InfraredfluxesareinJy–asobserved. ThisstarisfainterthanPM4butappearsredontheSSSimagesand
∗EyeballestimateforPM7. isunresolvedinbothSSSand2-MASSdata.Itcouldbetheprimary
(cid:4)C 2003RAS,MNRAS341,961–972
970 Q.A.ParkerandD.H.Morgan
sourceofthenear-infraredflux.However,itisnotexpectedtomake ∼−1.0wasderivedfromtheapparentVmagnitudeafterapplying
asignificantcontributiontotheMSSSOspectrumdescribedearlier. adjustmentstoaccountfortheemissionlines,calculatedfromthe
The position of PM7 in the (J − H) − (H − K) diagram is Hβ flux and spectral line ratios seen in the spectrum published
alsoclosetothesequencesofcoolstars.Thedatapresumablyrelate byVassiliadisetal.(1992),andfromthecontinuumfromthegas,
totheclosecompaniondiscussedearlier.The(V − K)and(R − estimatedfromtheHβfluxasperformedforPM3butnowincluding
K)coloursareconsistentwiththoseofanMstarwithlittleorno two-photonemission.Thedistancemoduluswastakentobe18.94
reddening(Bessell1991). (Westerlund 1997) and interstellar extinction was assumed to be
negligible(Vassiliadisetal.1992).
7.3.2 InfraredIRASandMSXphotometry
7.5 Interstellarextinction
TheIRASPointSourceCatalogueprovidesatleastonegoodquality
setofmeasurementsforthreeofthePNe.OnlyPM6wasundetected; Estimatesoftheextinctionarereadilycalculatedfromthevandr
norwasitseenintheFaintSourceCatalogue.ThecataloguedIRAS magnitudesderiveddirectlyfromthespectrophotometryandindi- Do
w
fluxes,uncorrectedforcoloureffects,arequotedinTable6.There rectlyfromthebroad-bandphotometryasoutlinedabove.Thiswas n
are no appropriate IRAS detections in the Small-Scale Structure performedusingtheintrinsicparametersdiscussedaboveandthe loa
d
Catalogue.ThefluxratiosfortheIRASbandsaftercorrectionfor propertiesoftheextinctionlawasinPaper1.OnlyforPM3with ed
colourtemperatureeffectsprovideblackbodytemperaturesforthe its bright unresolved central core, was it necessary to correct the fro
dust emission (T ). These were derived from the 25- and 60-µm photometryforcontributionsfromthenebularcontinuum. m
d h
fluxesusingaλ−1 emissivity(Stasinska&Szcerba1999)andare Theextinctiontowardsthesestarscanalsobededuced,inprin- ttp
qraunogtee,dwinhicthheissnuomrmmaalryfotraPbNlee.wThitehyWmRoCstPlyNfSal(lGionrnthyeet7a5l–.1200501K). cpiopslsei,bfleroomnltyhefoBraPlMme3rblienceaursaetiothseooftthheernneebbuullaa.eHhaovweewveera,kthliisneiss s://ac
a
However,sincethisfluxratiocanonlygiveanupperlimitforPM7, orareuncalibrated(PM4).InthebrightcentralzonearoundPM3, d
e
tohtehe1r0W0-RanCdS6P0N-µ,mbufltunxoetslwowereeruthseadnisnosmteeado.fTthdeisclooowleesrtthnaonrmfoarl tghiveemseAasvu=red4.H0αm/Hagβ,rHaβtioisgitvoeoswAeva=ki3n.3thmeaoguatenrdntheebuHlaγt/oHβperramtiiot mic.o
PNOe.nly PM4 appears in the MSX survey; the others, although in magaogoidscmoenassiustreenmtewnitthofwthheateixstisnecetnio.nThtheefraec,tbtuhtactetrhteaipnrloyfiAlevi=nH3.γ3 up.com
the region mapped, are all too faint as is evident from their low isidenticaltothatinHβshowninFig.3andtheIRASfluxissmall, /m
IRAS fluxes. The MSX images of PM4 at 8 and 21 µm can be suggestthatthereisnogreatquantityofdustintheouternebula. nra
viewedinthepaperbyCohen&Parker(2003).The8-µmimage UpperlimitsforAvcanbederivedforPM6and7usingmeasure- s/a
is the weaker and smaller, being 4 pixels across compared with mentsoftheHα fluxesandestimatedupperlimitsfortheunseen rtic
6pixels(1MSXpixel≡6arcsec).Withtheopticalimagecovering Hβflux.So, Av(cid:2)2.4forPM6and Av(cid:2)4.7forPM7. le-a
∼3MSX pixels)andtheMSX resolutionbeing3pixels,a6-pixel Adopted values of the extinction are given in Table 7, which bs
MSXimageisnotunexpectedforPM4.Thatis,thereisnoevidence provides a summary of the properties of the four new CPSN and tra
c
thatthemid-infraredemissionextendsmuchbeyondtheoptically includesthetwofromPaper1forcompleteness.Thevaluesof Av t/3
detected nebula. The 12-µm image is similar in size to the 8-µm calculatedfromthebroad-bandphotometryforPMR1and2arein 41
imageandthe15-µmimageissimilartothe21-µmimage.Ascan goodagreementwiththosederivedinPaper1fromthespectropho- /3/9
beseeninTable6,theMSXandIRASfluxesforPM4areinexcellent tometry.ThisisnotsoforPM3,probablybecausethecorrections 61
agreement. tothebroad-banddataaretoolargetoyieldareliablecolour.So, /10
0
Av for PM3 is an average of the spectrophotometric and Balmer 7
1
decrement estimates. The corrected broad-band value is the only 5
0
7.4 Absolutemagnitudesandintrinsiccolours oneavailableforPM4;PM6hasanaverageofthebroad-bandand b
y
spectrophotometricdata.PM7,whichhasnocolourmeasurement, g
Intrinsiccoloursandabsolutemagnitudesareneededbeforeextinc- ue
hasavaluesetsomewhatarbitrarilyalittleabovetheupperlimit s
tionanddistanceestimatescanbemade.Thesearebestknowninthe derivedfromtheBalmerdecrement. t o
vrsystem.ThesamevaluesaswereusedinPaper1forthe[WC4] n 0
starPMR1havebeenusedforthethree[WC4]starsinthispaper 9 A
(+se0e.5t.hediscussioninPaper1).Thatis,(v −r)o =−0.23, Mv = 7.6 Linediagnostics pril 2
0
PM4 is classed as [WC8] and its absolute magnitude can be Thestrengths(equivalentwidthsWλandFWHMmeasures)ofthe 19
estimatedfromtwosources.First,forthe[WC8]starNGC40,it CIVλ5808andCIIIλ5696emissionlinesseeninWRspectracan
canbeshownthatMv=0.0usingphotometryfromCrowtheretal. be indicators of whether the star is indeed a CSPN or in fact a
(1998)andadistanceof1.2kpcfromTajitsu&Shin’ichi(1998). PopulationIstarwitharingnebula.AlthoughthelinesinCSPN
Secondly,analternativeestimateofMv∼−1.0wasprovidedbythe aregenerallyweakerthaninPopulationIstars,thereisanoverlap
SMCPN,MG08≡Ln302(Morgan&Good1985),whichhasa betweenthetwostellarpopulations.W inearlyPopulationIWC
5808
[WC8]centralstar(Monk,Barlow&Clegg1988)andisataknown starsisusuallyintherange500–3000A˚ (Smithetal.1990),whereas
distance.AnaverageMv∼−0.5wasfinallyadoptedforPM4and forthe[WC]starsitisintherange50–2500A˚ (Tylendaetal.1993;
itsintrinsiccolourwastakentobe(v−r) =−0.23(seePaper1). Crowtheretal.1998),theupperpartbeingtheexceptionratherthan
o
ThesecondestimateofMvwasmadefrommeasurementsmade therule.Similarly,theFWHMvaluesareusuallyabove50A˚ for
bytheSuperCOSMOSmachineofaV platetakenwiththeUKST thePopulationIstarsandbelow50A˚ forthe[WC]stars.Hence,
andcalibratedusingcharge-coupleddevice(CCD)photometricdata PM3,6and7havelinesthataretooweakforthemtobePopulation
from the Guide Star Photometric Catalogue II (Bucciarelli et al. Istars.Similarly,thenarrowlinesinPM4aremoreappropriateto
2001).Theseyielded V = 17.61. Theabsolute magnitudeof Mv aCSPN.
(cid:4)C 2003RAS,MNRAS341,961–972