The detection of C60 in the well-characterized planetary nebula M1-11

1.1 MB·English

by  Masaaki Otsuka

PreprinttypesetusingLATEXstyleemulateapjv.5/2/11
THEDETECTIONOFC60INTHEWELL-CHARACTERIZEDPLANETARYNEBULAM1-11
MASAAKIOTSUKA1,2,F.KEMPER1,S.HYUNG3,B.A.SARGENT2,4,M.MEIXNER2,A.TAJITSU5,K.YANAGISAWA6
1InstituteofAstronomyandAstrophysics,AcademiaSinicaP.O.Box23-141,Taipei10617,Taiwan,R.O.C.;[email protected]
2SpaceTelescopeScienceInstitute,3700SanMartinDrive,Baltimore,MD21218,U.S.A.
3SchoolofScienceEducation(Astronomy),ChungbukNationalUniversity,CheongJu,Chungbuk361-763,Korea
4CenterforImagingScienceandLaboratoryforMultiwavelengthAstrophysics,RochesterInstituteofTechnology,54LombMemorialDrive,Rochester,NY
14623,USA
5SubaruTelescope,NAOJ,650NorthA’ohokuPlace,Hilo,Hawaii96720,U.S.A.and
6OkayamaAstrophysicalObservatory(OAO),NAOJ,Kamogata,Okayama719-0232,Japan
3
(Received;Revised;Accepted)
1
0
ABSTRACT
2
We performed multiwavelength observations of the young planetary nebula (PN) M1-11 and obtained its
n
elementalabundances,dustmass,andtheevolutionarystatusofthecentralstar. TheAKARI/IRC,VLT/VISIR,
a
andSpitzer/IRSspectrashowfeaturesduetocarbon-richdust,suchasthe3.3,8.6,and11.3µmfeaturesdue
J
topolycyclicaromatichydrocarbons(PAHs), a smoothcontinuumattributableto amorphouscarbon,andthe
9
broad11.5and30µmfeaturesoftenascribedtoSiCandMgS,respectively. Wealsoreportthepresenceofan
2
unidentifiedbroadfeatureat16–22µm,similartothefeaturefoundinMagellanicCloudPNewitheitherC-rich

orO-richgas-phasecompositions. We identifyforthe firsttimeinM1-11spectrallinesat8.5(blendedwith
]
R PAH),17.3,and18.9µmthatweattributetotheC60fullerene.Thisidentificationisstrengthenedbythefactthat
otherGalacticPNeinwhichfullerenesaredetected,havesimilarcentralstars,similargas-phaseabundances,
S
and a similardust compositionto M1-11. The weak radiationfield due to the relativelycoolcentralstars in
.
h thesePNemayprovidefavorableconditionsforfullerenestosurviveinthecircumstellarmedium. Usingthe
p photo-ionizationcodeCLOUDY,combinedwithamodifiedblackbody,wehavefittedthe∼0.1–90µmspectral
- energydistributionanddeterminedthedustmassinthenebulatobe∼3.5×10- 4M . Ourchemicalabundance
o ⊙
r analysisandSEDmodelsuggestthatM1-11isperhapsaC-richPNwithC/Oratiointhegas-phaseof+0.19
t dex,andthatitevolvedfroma1–1.5M star.
s ⊙
a Subjectheadings:ISM:planetarynebulae:individual(M1-11),ISM:abundances
[

1
1. INTRODUCTION coolcentralstar(29300K, Phillips2003),andthe nebulais
v relativelycompact,withasizeof.6′′indiameterinHαemis-
4 ThemoststablefullereneisC60 (Draine2011). Fullerenes sion,anditappearstobeaveryyoungobject(∼1000yrafter
0 togetherwithothercarbondustsuchasgraphiteareexpected
leavingtheAGBphase,thispaper).Henryetal. (2010)mea-
1 tobeimportantcomponentsoftheinterstellarmedium(ISM),
sured the C abundance in M1-11 using recombination lines
7 because they contribute to interstellar extinction. For exam-
(RLs) and the O abundance with collisionally excited lines
. ple, Dopitaet al. (1997)arguedthe possibilitythatthe deep
1 (CELs, number density ratio of C/O = 79.4). To date, only
0 2200Åabsorptionfeatureinthelow-excitationplanetaryneb- upper limits to the intensities of the CELs C III] 1906 and
3 ula(PN)SMP LMC8mightbebyasurfacechargeslop res-
1909Å areobtained(Kingsburgh&Barlow 1994),andthus
:1 aornoaunncde tohnisCw60a.velTenhgethgrdapuheitteogπr→ainπs∗healveectaronspeexctcriataltpioenask. thegasphaseC/OratioofM1-11derivedfromthesametype
v of emission line is still unknown. However, M1-11 is also
Fullerene and polycyclic aromatic hydrocarbons(PAHs) re-
i known to be a dust-rich PN, showing predominantly C-rich
X semblegraphite;thereforesuchgrainshavestrongelectronic
dust. Silicon carbide (SiC) and amorphous silicate features
transitionsaround2200Å(Draine2011).Theinvestigationof
r areseenintheIRAS/LRSdata(Zhang&Kwok1990).Asig-
a circumstellarcarbongrainssuchasC wouldbeimportantto
60 nificantnear-infraredexcesssuggeststhepresenceofhotdust
understandISMevolutionmoredeeply.
(Phillips & Ramos-Larios 2005; Zhang & Kwok 1990), al-
RecentSpitzer/IRSstudiesshowthatfullerenesC arede-
60 thoughthereisalsoacontributionfromthe3.3 µmemission
tectedinseveralyoungPNe,aproto-PN,andtwopostasymp-
feature due to PAHs in the near infrared(Allen et al. 1982).
totic giantbranchstars (postAGB) in the MilkyWay (Cami
Longerwavelengthemissionfeaturesat6.2,6.9,7.7,and8.6
et al. 2010; García-Hernándezet al. 2010; Zhang & Kwok
µmduetoPAHsarereportedbyCohenetal. (1986). Avery
2011; Gielen et al. 2011) and also in a handfulyoung PNe
weakandtentativefeatureisseenaround6.9-7.0µm(seeCo-
in the Magellanic Clouds (García-Hernández et al. 2011a;
hen et al. 1986). Indeed, there are other C transitions at
Bernard-Salaset al. 2012). The detectioncases are increas- 60
7.0and8.5µmbutCohenetal. (1986)showsomeevidence
ing,howevertheexcitationandformationmechanismisstill
(althoughthequalityoftheirdataisnotsatisfactory)forapos-
unclear(e.g.,Camietal.2011;García-Hernández2012).The
sibledetectionalsoinM1-11. Therefore,M1-11isperhapsa
detectionsgenerallysuggestthatfullerenescansurviveorbe
C-richPN.
observedinaC-richenvironmentwithaweakradiationfield.
To confirm whether C in M1-11 is real and also obtain
M1-11(PN G232.8- 04.7)is a good sample in C forma- 60
60 insightsaboutC formation,weneedtoinvestigatethephys-
tioninacircumstellarenvironment,becausemostoftheC 60
60 ical and chemical properties of the dust and ionized nebula
PNehavecoolcentralstars(∼30,000K)andC-richnebulae,
and the nature of the central star, then we need to compare
andtheyareveryyoung(∼1000yr). Indeed,M1-11hasthe
2 Otsukaetal.
thederivedquantitieswiththoseinC PNe. Tocharacterize signal-to-noiseratio(S/N)ofthecontinuumisnecessary. The
60
M1-11,weobtainedcontinuousdatafromtheUVtothefar- resulting S/N after subtraction of the sky background was
infrared using several instruments, and we comprehensively foundto range from ∼5 at ∼3700 Å to ∼30 at ∼5200 Å in
investigatedthisPN. thebluespectrum,andfrom ∼5at∼4800Åto15at∼6700
Inthispaper,wediscussC inM1-11basedontheinfor-
60 Åintheredone.
mationofthedustandgascompositionsandtheevolutionary
Data reduction of the Subaru/HDS spectra and analysis
status of the central star. In section 2, we describe the UV-
of the emission lines was done with the long-slit reduction
tomid-infrared(mid-IR)spectroscopicdatafromtheInterna-
packagenoao.twodspecavailableinIRAF7,andwasper-
tional Ultraviolet Explorer (IUE), Subaru/HDS, OAO/ISLE,
formed in the same manner as described by Otsuka et al.
AKARI/IRC,VLT/VISIR,andSpitzer/IRS,aswellasnarrow-
(2010). Whenmeasuringthefluxesoftheemission-lines,we
band imaging obtained with WFPC2 on the Hubble Space
assumedthattheline profileswereGaussianandweapplied
Telescope (HST). The description in Section 2.6 includes a
amultipleGaussianfittingtechnique.
listofdustfeaturesseeninM1-11,specifically,wereportthe
Thelinefluxeswerede-reddenedusing
discovery of weak features at 8.5, 17.3 and 18.9 µm lines,
which are attributed to the C fullerenes. The derivationof I(λ) F(λ)
60 log =log +c(Hβ)f(λ), (1)
the ionic and elemental abundances in the ionized nebula is 10(cid:20)I(Hβ)(cid:21) 10(cid:20)F(Hβ)(cid:21)
givenin Section 3. In Section 4, we discuss the observedC
andOgasabundancesandcomparethemwiththepredictions whereI(λ)andF(λ)arethede-reddenedandtheobserved
fromnucleosynthesismodelsforAGBstars.Usingthephoto- fluxes at λ, respectively, and f(λ) is the interstellar extinc-
ionizationcode CLOUDY (Ferlandetal. 1998),wefitted the tionparameteratλ,fromthereddeninglawofCardellietal.
spectral energy distribution (SED) and determined the dust (1989) with RV = 3.1. The interstellar reddening correction
massandtheevolutionarystatusofthecentralstar. Section4 wasperformedusingthereddeningcoefficientc(Hβ),atHβ.
alsoincludesadiscussionontheformationofC ,andacom- We compared the observed Balmer line ratios of Hγ (blue
60
parisonofthephysicalpropertiesofM1-11tothoseofother spectrum) or Hα (red spectrum) with Hβ to the theoretical
GalacticPNethatexhibitfullerenefeatures. Asummaryand ratio computed by Storey & Hummer (1995) assuming the
futureprospectsaregiveninSection5. electron temperature T = 104 K and the electron density n
e e
=104 cm- 3 assumingthatthenebulaisopticallythickinLy-
2. OBSERVATIONSANDDATAREDUCTION α (Case B of Baker & Menzel 1938). We derived c(Hβ) =
2.1. Subaru/HDSobservations 1.677±0.008fortheblueand1.218±0.017fortheredspec-
tra.
We obtained optical spectra of M1-11 using the High-
Thefluxscalingwasperformedusingallemissionlinesde-
DispersionSpectrograph(HDS;Noguchietal.2002)attached
tectedintheoverlapregionbetweentheblueandtheredspec-
tooneofthetwoNasmythfociofthe8.2-mSubarutelescope,
tra. Thede-reddenedrelativeintensitiesI(λ)detectedinboth
on October 6, 2008 (programID: S08B-110, PI: M.Otsuka)
spectra are consistent within 10% of each other. The com-
andOctober18,2005(PI:A.Tajitsu). Thespectraweretaken
bined de-reddened spectrum is presented in Fig. 1, and the
in two wavelength ranges: 3600–5400 Å (the blue spectra, detectedlinesarelistedintheAppendix(Table16). Wehave
taken in 2008) and 4600–7500 Å (the red spectra, taken in detectedover160emissionlines,thusexceedingthenumber
2005). of detections by Henry et al. (2010), who report more than
Whenweobtainedthebluespectra,anatmosphericdisper- 70 lines in the 3700–9600Å spectra. Our measurements of
sioncorrector(ADC)wasusedtominimizethedifferentialat- thelineintensitiesI(λ)areinagreementwiththeresultsfrom
mosphericdispersionoverthe broadwavelengthregion. We Henryetal.(2010)withina∼14%error.
used a slit width of 1.′′2 (0.6 mm) and a 2×2 on-chip bin- Specifically,wedetectedCII,NII,andOIIRLs,andhighly
ning. We set the slit length to be 8′′ (4.0 mm), which fitted excitedlinesduetoHeII,CIII,andNIII. Thesehighexcita-
thenebulawellandallowedustodirectlysubtractskyback- tionlinesshowarelativelybroadFWHM(∼0.8-1.6Å)com-
groundfromtheobjectframes. Theslitpositionangle(P.A.)
paredtotypicalnebularlines(∼0.2–0.5Å).Itispossiblethat
was ∼225◦. The CCD sampling pitch along the slit length
projectedonthe skywas ∼0.′′276perbinnedpixel. There- theHeII,CIII,andNIIIlinesarenotofnebularoriginbutof
stellarorigin,becausetheeffectivetemperatureofthecentral
solving power reached around R >33000, which is derived
star(29300K;Phillips2003)isnothighenoughforspecies
from the mean of the full width at half maximum (FWHM)
withanionizationpotential(IP)&40eVtoexistinthenebula.
of narrow Th-Ar and night sky lines. The total exposure
Forexample,wedidnotdetectanynebularlinesfromspecies
time was 600 sec (=300 sec ×2 frames). For the flux cali-
withanIP&40eV,suchas[NeIII]λλ3876/3967(IP>41eV)
bration,blazefunctioncorrection,andairmasscorrection,we
and[ArIV]λ4711/40(>40.7eV).TheIPsofHeII,CIII,and
observedG192B2Basastandardstar.
NIIIare54.4,47.9,and47.5eV,respectively.
Fortheredspectra,weusedtheredimagede-rotatorandset
For our analysis, we also used the emission-line fluxes in
ittoP.A.=90◦. Wesettheslitwidthto0.′′6andtheslitlength
to7′′ andselecteda1(wavelengthdispersion)×2(spatialdi- the 7700–9300 Å range measured by Henry et al. (2010)
scaledinsuchawaythattheshorterwavelengthpartoftheir
rection)on-chipbinning. TheresultingspectralresolutionR
spectrummatchesourHDSobservations.
is >65000. We used an exposure time of 300 sec and ob-
servedG192B2Basastandardstar.
2.2. HST/WFPC2archivedata
Forbothsetsofobservations,wetookseveralbias,instru-
mental flat lamp, and Th-Ar comparison lamp frames. We
7 IRAFisdistributedbytheNationalOptical AstronomyObservatories,
are interested in detecting weak C, N, and O recombination
whichareoperatedbytheAssociationofUniversitiesforResearchinAstron-
lines. The peak intensities of these lines are typically ∼10- omy(AURA),Inc.,underacooperativeagreementwiththeNationalScience
20% higher than the local continuum, and therefore a high Foundation.
ThedetectionofC inthePNM1-11 3
60
FIG.1.—Thescaledandde-reddenedHDSspectrumofM1-11.Thewave-
lengthisshiftedtotherestwavelengthinair.
We downloaded archival HST/WFPC2 photometry in the
F656N(6564Å/28Å)filter(P.I.:R.Sahai;PID:8345),which
tracestheHαemission. Wereducedthephotometricdataus-
ingthestandardHST pipelinewithMultiDrizzle,andpresent
thedrizzledM1-11F656NimageinFig.2. Theplatescaleis
0.025′′pixel- 1. TheimageshowsthatM1-11isanelongated FIG.2.—HST/WFPC2F656NimageofM1-11,rotatedaccordingtoelon-
nebula; the dimensions of the bright rim are ∼0.8′′ along gationofthenebula. Intheinner2′′×2′′box,thegrayscaleisadjustedto
showthebrightnessofthebrightrimandthecentralstar. Theradialprofiles
P.A.=–27◦and∼0.5′′alongP.A.=+63◦. inHαandn(H+)fromA(Dec.relativeposition=–0.5′′)towardsB(–2.7′′)
arepresentedinFig.3(a)and(b),respectively.
2.2.1. ThetotalHαandHβfluxes
withT =5400KderivedfromtheBalmerjump(Seesection
e
The de-reddening formula (eq. (1)) requires the total Hβ 3.2),D=2.1kpc(Tajitsu&Tamura1998),andassumingn
e
flux over the entire nebula to obtain the line fluxes in the ≃ n(H+), n(H+) can be written as a function of the distance
AKARI and Spitzer spectra. This can be derived from the fromthecentralstarRincmas
WFPC2 Hα image. We find thatthe totalfluxin theF656N
filter is 1.77(–11) ± 3.48(–13) erg s- 1 cm- 2 integrated over n(H+)≃3.74×1019 Il(Hα) 0.5. (4)
the entire PN (we will use the notation X(- Y) for X×10- Y, (cid:18) ǫR (cid:19)
hereafter),whereweassumethattheuncertaintycorresponds
The resulting n(H+) profile from A towards B with different
tothestandarddeviationofthebackground. UsingtheHDS
values for ǫ is presented in Fig. 3(b). If we assume that the
redspectrumandthe transmissioncurveofthe F656Nfilter,
ionized gas is concentrated within R=1.0′′ and that the den-
weestimated∼12.5%ofthetotalmeasuredfluxtobedueto
a localcontinuumandthe [NII] 6548Å line flux. Thus, we sity has a constant value of 105 cm- 3 obtained from Balmer
estimatedthesoloHαlinefluxtobe1.55(–11)ergs- 1 cm- 2. decrements,thenwefindthatǫisaround0.2. Weusedthese
UsingtheobservedF(Hα)/F(Hβ)ratio(6.57)intheHDSred n(H+)profileswithdifferentvaluesforǫintheSEDmodeling
spectrum,wederivethetotallogF(Hβ)tobe–11.629ergs- 1 (Seesection4.2).
cm- 2,whichiscomparabletologF(Hβ)=–11.84ergs- 1cm- 2
2.3. ISLEObservations
measuredbyCahnetal. (1992).
We obtained J and Ksband medium-resolution(R∼2500)
2.2.2. Thehydrogendensityprofile spectrausingthenear-infraredimagerandspectrographISLE
(Yanagisawa et al. 2006, 2008) attached to the Cassegrain
InFig.3(a),wepresenttheradialprofilefromAtowardB
focusofthe 1.88-mtelescopeattheOkayamaAstrophysical
indicated in Fig. 2. Based on this radial profile, we exam-
inedtheionizedhydrogendensity n(H+)asa functionofthe Observatory. Theobservationswere donein ISLE engineer-
ingtime in March2008(Ks) andJanuary2010(J). The de-
distance from the central star R. When we restrict the inte-
tectorofISLEisa1K×1KHgCdTeHAWAIIarray. Weused
grationtotheoptionalportionofthenebula,thede-reddened
a science grade detector for the J-band observations and an
observedHα flux using c(Hβ)=1.218andthe reddeninglaw
ofCardellietal. (1989)withR =3.1,I(Hα)inergs- 1 cm- 2 engineeringgradedetectorfortheKs-bandobservations.The
V l entranceslit widthwas 1′′ forbothsets of observations. We
isgivenby:
fixed the P.A. at 90◦ during the observations. The sampling
pitchesinwavelengthwere∼1.68×10- 4and∼3.4×10- 4µm
4πD2Il(Hα)=Z 4πj(Hα)ǫdVl, (2) pixel- 1 in the J and Ks spectra, respectively, while the sam-
pling pitch in the space direction was 0.′′25 pixel- 1 for both
whereDisthedistancetoM1-11fromus; j(Hα)istheemis-
spectra. We observed standard stars HIP35132 (A0V) and
sioncoefficient;andǫisthefillingfactorwhichisthefraction
HIP35180(A1V)fortheJ-bandandHIP31900(F0V)forthe
ofthenebularvolumefilledbyionizedgas. V isthevolume
l Ks-bandspectraatdifferentairmassestocalibratethefluxlev-
oftheofthenebula.InCaseB,
els,andcorrectfortelluricabsorptionandairmassextinction.
4πj(Hα) 104 - 1.077 We observedM1-11ina seriesof120sec exposuresinboth
≃3.856×10- 25 . (3) observing modes. The total exposure times were 3600 sec
n(H+)n (cid:18) T (cid:19)
e e
4 Otsukaetal.
FIG.4.—TheISLEJKs-bandspectraofM1-11.
BD+30◦3639;Hora&Latter1994forM2-9).Thedifference
FIG.3.—TheradialprofilesfromAtoB(Fig.2)inHα(upper)andn(H+) oftheexcitationtemperaturebetweendifferentrotationlevels
(lower)withdifferentfillingfactorsǫ.
(T ∼2150Kforv=1andT ∼1000Kforv≥2)indicates
rot rot
H linesarecollisionally(shock)excitedinapart(thecenter)
2
for the J-band spectra and 3480 sec for the Ks-band spec- of the nebula. However, it is evident that the UV excitation
tra, respectively. Dark frames with the same science expo- in PDR isstill dominantforthe mostpartof H emissionin
2
sure time, Ar and Xe lamp frames, and on- and off-dome M1-11.
flat frames were also taken. For furtherwavelength calibra- Any pure rotational lines in Spitzer/IRS are not detected
tionanddistortioncorrection,OH-linesrecordedintheobject (seeTable2).
frames were used. The data reduction was performed in a Thelinesat1.15and1.19µmareidentifiedwith[P II](in
standardmannerusingIRAF. Theinterstellarreddeningcor- the3P–1D and3P –1D transitions,respectively),represent-
1 2 2 2
rectedspectraarepresentedinFig.4(a)and(b). Forthiscor- ingthediscoveryoftheselinesinM1-11. Adoptingthetran-
rection,weadoptedc(Hβ)appliedintheHDSredspectrum. sitionprobabilitiesofMendoza& Zeippen(1982),the colli-
TheresultingS/Nsare>40intheJ-bandand>30inKs-band sional impacts of Tayal (2004a) and the level energy listed
spectraatthecontinuumlevel. in Atomic Line List v2.05b128, the expected [P II] I(1.19
We detectedmorethan50linesinthesespectra,including µm)/I(1.15µm) ratio is 2.63 in T=10000 K andn =5×104
e e
a series of vibration-rotation excited lines of molecular hy- cm- 3. The observedline ratio (2.79±0.44)agreeswell with
drogen (H2), as listed in the Appendix (Table 17). The line thetheoreticalvalue,whichconfirmstheidentificationofthe
fluxes were normalized such that I(Paβ)=100 in the J-band [P II]1.15/1.19µmlines. Ourmeasurementofthe I([KrIII]
andI(Brγ)=100intheKs-bandspectra. 2.19µm)/I(Brγ)ratioof3.44±0.23alsoagreeswithSterling
Fig.5showsthespatialprofilesofBrγ andH2 1-0S(1)/2-1 &Dinerstein(2008;3.22±0.26).
S(1)linesintheK-bandspectrum.Inthebothspectra,theH
2
lines are easily distinguished with other ionic lines by their 2.4. IUEarchivaldata
spatialspreadupto∼16′′inthediameter.TheratioofH21-0 TheN2+ abundancecanbeestimatedfromtheNIII]λ1750
S(1)/2-1S(1)isatraditionalshockindicator(e.g,Hora&Lat-
line,presentinarchivalIUEspectrawhichweretrievedfrom
ter1994,1996;Kelly&Hrivnak2005).TheratioinM1-11is
the Multi-mission Archive at the STScI (MAST). We col-
∼4.5atthecenterofthenebula,anditdecreasesupto ∼1.0
lected low-resolution IUE spectra taken by the Short Wave-
outside of the ionized region. The ratio of H 1-0 S(1)/2-1
2 lengthPrime(SWP)andLongWavelengthPrime(LWP)cam-
S(1) = 4.5 along the optical nebula (.6′′ in diameter) indi-
eras(fileID:SWP25846,LWP05896,andLWP05897),allof
catesamixofUVandshockexcitation(thisisusualinproto-
whichweremadeusingthelargeaperture(10.3×23arcsec2).
PNe,e.g.,Kelly&Hrivnak2005).Furthermore,thedetection
ofaseriesofH lineswithuppervibrationallevel(v≥3)in In these spectra, we identified the He II 1640 Å and N III]
2
J-band indicates that these lines are excited by fluorescence 1750Ålines.Wedeterminedthatc(Hβ)=0.67±0.12,bycom-
throughtheabsorptionofUVphotonsfromthecentralstarin paringthetheoreticalratioofHeIII(λ1640)/(λ4686)=6.56to
photodissociationregion(PDR). theobservedvalue,inthecaseofTe=104Kandne=104cm- 3
The excitationdiagram of H lines in the entire slit of the as given by Storey & Hummer (1995). The interstellar ex-
2
spectra is shown in Fig.6. An ortho-to-pararatio of 3 is as- tinction correction was made using equation (1). The flux
sumed.Itclearlyshowsthatthevibrationalexcitationtemper- measurementsofthedetectedlinesalongwiththenormalized
ature(T )exceedstherotationexcitationtemperature(T ),
vib rot
indicating fluorescence emission (cf. Shupe et al. 1998 for 8seehttp://www.pa.uky.edu/∼peter/newpage/
ThedetectionofC inthePNM1-11 5
60
TABLE1
LINESDETECTEDINTHEIUESPECTRA.
λlab Ion f(λ) F(λ)a I(λ)
(Å) (ergs- 1cm- 2) (I(Hβ)=100)
1640 HeII 1.177 5.03(–14)±9.99(–15) 0.51±0.20
1750 NIII] 1.154 1.51(–13)±1.52(–14) 1.48±0.51
alogF(Hβ)=–11.63ergs- 1cm- 2.
tion, we used the IRC Spectroscopy Toolkit for the Phase 3
dataversion.Fig.7showstheIRCspectrumwithalocaldust
continuum subtracted. The S/N is >30 for the dust contin-
uum. Several prominent lines are visible, and their central
wavelengths are indicated by dotted lines. The line fluxes
are listed in Table2. For the IRC spectra, we derived that
c(Hβ)=1.40±0.03bycomparingtheobservedintensityratios
ofHI4–5(Brα4.051µm),4–6(Brβ2.625µm),and5–7(Pfβ
4.653µm)toHβandthetheoreticalvaluesofStorey&Hum-
mer(1995)forthecaseof104Kand104cm- 3. Tocorrectfor
interstellar reddening, we used the ratio of the extinction at
eachwavelengthtotheB- V colorexcess,Aλ/E(B- V),given
by Fluks et al. (1994), in combination with the correlation
betweenHβ andthecolorexcess,c(Hβ)=1.47E(B- V),from
FIG.5.—SpatialprofilesofBrγ(upperpanel),H21- 0S(1)and2- 1S(1) Seaton(1979).
lines(lowerpanel)alongtheslitintheK-bandspectrum.Aftersubtractedthe In the AKARI spectra we also found an emission band at
0coSn(1ti)n.uum,profilesarenormalizedbytheintensitypeakofBrγ andH21- 3.2–3.6µm,whichmaybeduetoaromaticandaliphatichy-
drocarbonspecies. AsimilarfeatureisseeninPNNGC7027
and proto-PN (PPN) IRAS21282+5050, the latter of which
hasa[WC11]centralstar. ISO/SWSarchivalspectraofNGC
7027andIRAS21282+5050areshownforreferenceinFig.7.
The resonance at 3.3 µm is attributed to vibrational transi-
tionsinpolycyclicaromatichydrocarbons(PAHs;e.g.Draine
2011). We also recognize the 6.2, 7.7, and 11.3 µm reso-
nances due to PAHs in the spectra of M1-11. In particular,
the 11.3 µm C-H out-of-plane bending mode is seen in the
Spitzer/IRSspectrum(Seenextsection). Cohenetal. (1986)
already detected the 6.2, 6.7, 7.7, and 8.6 µm resonancesin
M1-11. The 3.3 µm band profile of M1-11 is similar to the
onesseen in NGC 7027 and IRAS 2182+5050,and thus we
assumethattheemissionseeninM1-11isalsoduetoPAHs.
Indeed, the 3.3 µm feature was first detected by Allen et al.
(1982),whoalsomeasureditsflux. Usingthetheoreticalin-
tensity ratio of H I I(5–9) to I(5–11) = 1.86 in the case of
T=104Kandn =104cm- 3,weremovedthecontributionfrom
e e
FIG.6.— MolecularhydrogenexcitationdiagramfromthefullJ-(opencir- HIn=5–9tothe3.3µmfeatureandestimatedthefluxdueto
cles)andK-band(filledcircles)spectra.Shownaretheupperstatevibration- PAHsI(PAH3.3µm)tobe7.63(–12)ergs- 1 cm- 2,whichis
rotation level populations relative to that in the v=1, J=3 level plotted
againsttheenergyoftheupperstateinKelvin(K).gisthestatisticalweight. abouttwiceaslargeasthemeasurementbyAllenetal.(1982;
Anortho-to-pararatioof3isassumed. Thepointswithinvibrationallevels 3.1(–12)ergs- 1cm- 2).
fallonseparatelines, asexpected fluorescent-excited emission. Linearfits
tothedataoneachvibrational level areplottedwiththederivedrotational
temperatures. 2.6. Spitzer/IRSandVLT/VISIRarchivaldata
M1-11 was observed by Spitzer on November 10, 2006
valuesarelistedinTable1. WhilewedidnotdetecttheCIII]
with the 9.9-19.6 µm (SH) and 18.7-37.2 µm (LH) modes
λλ1906/09ÅlinesintheSWPandLWPspectra,Kingsburgh
on the Infrared Spectrograph (IRS, Houck et al. 2004), as
& Barlow (1994) show I(C III]λλ1906/09) to be 6 with an part of program ID 30430 (PI: H. Dinerstein; AORKEY:
uncertaintygreaterthanafactorof2.
19903232).Wedownloadedthearchivalspectralimages,and
aftermaskingbadpixelsusingIRSCLEAN,weextractedthe
2.5. AKARI/IRCarchivaldata
one-dimensionalspectrausingSPICE.TheS/Nis>30forthe
Weanalyzedthe2.5–5.5µmprismspectraofM1-11taken dustcontinuum.
with the Infrared Camera spectrograph (IRC; Onaka et al. InthespectrumofCohenetal.(1986),veryweakandtenta-
2007)onboardoftheAKARIsatellite(Murakamietal.2007). tivefeaturesareseenaround7.0and8.5µmthatmayariseat
The data were obtained as part of a mission program, PN- leastpartiallyfromfullereneC withpossibleblendingfrom
60
SPEC (data ID: 3460037, PI: T.Onaka), on April 11, 2009. the PAH 8.5µm band. However, the quality of theirdata is
The used observingwindowwas 1′×1′. For the data reduc- insufficient to be confident of these features. To check the
6 Otsukaetal.
FIG.7.— Comparison of the AKARI/IRC spectrum of M1-11 (upper
line), the archival ISO/SWS spectra of the PN NGC7027 and the PPN
IRAS21282+5050 (middle&lower). Theidentified lines areindicated by
thethebrokenlines.TheIDsareindicatedbylowercaseletters;a:Brβ2.63
µm;b:HI5-112.86µm;c:PAH3.29µmC-Hstretch+HI5-93.29µm;d:
PAH3.38/3.40µmasymmetricCH3,CH2stretch;e:PAH3.46µmloneC-H
stretch;f:PAH3.49/3.51µmsymmetricCH3,CH2stretch;g:PAH3.56µm
aldehydesC-Hstretch;h: HI6-19,203.63µm;j: Brα4.05µm;k: HI4- FIG.8.—TheSpitzerspectraofM1-11(blackline)andM1-12(grayline).
5,6-144.05µm;l:HeI3-54.30µm;m:HI6-124.38µm;n:Pfβ4.65µm (innerbox)Theline-profilesofC6017.33and18.94µm.Theline-profilesof
(Referenceofthewavelengthofthehydrocarbonlines:Kwok2007). C60at8.5µminM1-11andM1-12arepresentinFig.10.
presenceof the C 8.5µm feature,we downloadedthe7.7-
60
13.3µmarchivalspectraldataobtainedusingtheVLT spec-
TABLE2 trometerandimagerforthemid-infrared(VISIR)atESOVLT
DETECTEDLINESINTHEAKARI/IRC,Spitzer/IRS,ANDVLT/VISIR UT3(ID:084.D-0868A;PI:E.Lagadec).Wereducedtheraw
OBSERVATIONS. datausingESOgasgano. TocomparetheVISIRdatawith
the Spitzer spectra of other C PNe and also to combine it
λvac Ion f(λ) F(λ)a I(λ) 60
(µm) (ergs- 1cm- 2) (I(Hβ)=100) withtheM1-11’sSpitzer spectrum,wedegradedtheoriginal
VISIRspectralresolvingpowerof∼400downto90byusing
2.63 HI(Brβ) –0.955 2.09(–12)±2.32(–13) 4.1±0.5 aGaussianconvolutiontechnique.TheS/Noftheconvoluted
2.86 HI5–11 –0.962 6.12(–13)±8.41(–14) 1.2±0.2
3.29 PAH –0.971 8.81(–12)±2.55(–13) 16.2±1.0 VISIRspectrumis>70.
+HI5–9 TheIRSandVISIRcombined7.7-37.2µmspectrumwhich
3.41 PAH –0.973 1.47(–12)±2.98(–13) 2.7±0.6 is shown in Fig. 8, reveals the solid-state/molecularfeatures
3.49 PAH –0.974 2.04(–12)±3.77(–13) 3.7±0.7
andatomiclinesonthedustcontinuumthermalemission.The
3.56 PAH –0.975 6.92(–13)±3.47(–13) 1.3±0.6
3.63 HI6–19 –0.976 1.59(–12)±4.08(–13) 2.9±0.8 detectedlinesarelistedinTable2. Theemissionaround8.5
+HI6–20 µmisthecomplexofC60 8.5µmandPAH8.6µm. Wemea-
3.73 HI5–8 –0.977 1.06(–12)±4.58(–13) 1.9±0.8 suredthefluxdensityofC 8.5µmbyusingmultipleGaus-
33..8921 HHII66––1165 ––00..997789 16..1295((––1123))±±85..3480((––1133)) 21..11±±11..50 sian fitting to separate its fl60ux from the PAH 8.6 µm feature
4.05 HI(Brα) –0.980 4.94(–12)±7.94(–14) 8.9±0.5 (See section 2.6.3). We performedthe interstellarreddening
+HI6–14 correction in a similar way as described in Section 2.5. By
44..3380 HHeII63––152 ––00..998822 56..7927((––1133))±±76..0572((––1144)) 1.30.1±±01..14 comparingtheobservedintensityratiosH IF(n=6–7)/F(Hβ)
4.65 HI(Pfβ) –0.984 8.99(–13)±1.17(–13) 1.6±0.2 & F(n=8–11)/F(Hβ) to the theoretical values of Storey &
+HI6–11 Hummer(1995) forthe case B assumption in Te=104 K and
88..56 CPA60Hbc ––00..997700 35..6160((––1122))±±45..5097((––1133)) 69..84±±01..90 ne=104cm- 3,wederivedthatc(Hβ)=1.63±0.02.
8.99 [ArIII] –0.959 1.60(–12)±1.75(–13) 3.1±0.4
12.37 HI6-7,8-11 –0.980 9.68(–13)±4.24(–14) 1.0±0.1 2.6.1. Broadspectralfeaturesat10–13and16–22µm
12.71 HeI –0.982 4.85(–13)±5.35(–14) 0.5±0.1 M1-11 appears to have C-rich dust, as evidenced by the
12.81 [NeII] –0.983 2.90(–11)±4.35(–13) 30.9±1.5
presence of a broad 10-13 µm feature, which is usually at-
1187.7.31 [CS60IdII] ––00..998811 14..3611((––1122))±±74..2778((––1143)) 14..49±±00..16 tributedtoSiCintheliterature.Thisfeature(centeredaround
18.9 C60e –0.981 6.88(–12)±2.55(–13) 7.4±0.4 11.3µm)is seenontopofa featurelesscontinuum,presum-
33.16 HeI –0.993 1.47(–12)±2.57(–13) 1.5±0.3 ablyduetoamorphouscarbon(AC).ThePAHfeaturesaround
35.83 HeI –0.993 3.89(–12)±2.85(–13) 4.0±0.3 10–11µm are also visible in the spectrum. A second broad
NOTE. — For interstellar reddening correction, we used feature is seen around approximately 16–22 µm, similar in
c(Hβ)=1.403±0.025 for the AKARI/IRC and 1.629±0.020 for the appearance to broad features reported in several PNe in the
Spitzer/IRCspectra,respectively.
MagellanicClouds(Stanghellinietal. 2007;Bernard-Salaset
alogF(Hβ)=–11.63ergs- 1cm- 2.
al. 2009; García-Hernándezetal. 2011a;García-Hernández
bTheFWHMis0.17µm.
cThesumoftwoGaussiancomponentsrepresentingthePAH8.6µm.See etal. 2012)
textindetail. WhileStanghellinietal.(2007)associatethisemissionfea-
dTheFWHMis0.51±0.04µm. ture with carbon-richdust, Bernard-Salaset al. (2009)show
eTheFWHMis0.36±0.03µm.
thatthe16–22µmbroadfeaturediffersfromthePAHplateau
ThedetectionofC inthePNM1-11 7
60
TABLE3 TABLE4
CANDOABUNDANCESDERIVEDFROMCELS,FORMAGELLANIC ADOPTEDOPTICALCONSTANTSFOREACHMODELDUSTCOMPONENT.
CLOUDPNESHOWINGTHE16–22µMFEATURE.
Dustspecies Datasource
Nebula Ca Oa C/O Ref.
SiC Pegourie(1988)
SMC1 8.11 8.26 0.71 (1) amorphouscarbon(AC) Rouleau&Martin(1991)
SMC6 8.03 8.22 0.65 (1) MgS Begemannetal.(1994)
LMC8 7.93 8.26 0.47 (2) HAC Honyetal.(2003)
LMC25 8.29 8.17 1.32 (3),(4)
LMC48 8.40 8.24 1.45 (3),(4)
LMC85 8.74 8.40 2.19 (2) dustgrainsisgivenby
REFERENCES. —(1)Idiartetal. (2007);(2)Dopitaetal. (1997);(3) 4 - 1
SatTahneghneulmlinbieertdaeln.s(i2ty00r5el)a;t(iv4e)Ltoeitshye&hyDdreongneenfeilsdd(e2fi0n0e6d)aslogH=12. Fλ= (cid:18)3πaiρiD2(cid:19) md,iQλ,iπBλ(Td,i), (5)
Xi
around16–20 µm (Van Kerckhovenet al. 2000) and the 21 whereaiisthegrainradiusofcomponenti,ρiisthedustden-
µm feature sometimes seen in carbon-rich post-AGB stars sity, md,i is the dust mass, Qλ,i is the absorption efficiency,
(e.g.Volketal.2011)andPNe(Honyetal.2001),andismore andBλ(Td,i)isthePlanckfunctionforadusttemperatureTd,i.
similartothe18µmamorphoussilicatefeature,thusassign- We adopt a distance D=2.1 kpc (Tajitsu & Tamura 1998).
ingaoxygen-richcarrierforthisfeatureinobjects. Bernard- In Table 4 we list the optical constants that we use for each
Salas et al. (2009)imply thatif the silicate identificationfor ofthedustspeciesconsidered. ForMgS,weusedtheoptical
thisfeatureiscorrect,theMagellanicCloudPNeoftenshow constants of nearly pure MgS, e.g. Mg0.9Fe0.1S, from Bege-
adualdustchemistry,althoughearlierinthesamestudythey mannetal. (1994). FortheHACs,weadopttheQλ ofHAC
state that not a single source in their sample shows a mixed inthecaseofH/(H+C)=0.3calculatedbyHonyetal. (2003).
chemistry, thus underminingthe silicate identificationof the In two models, we consider differentcompositions, consist-
16–22µmbump.Indeed,inacomprehensivestudyofalarge ingof combinationsofPAHs, amorphouscarbon(AC),SiC,
sample of Galactic and Magellanic Cloud PNe, Stanghellini MgS,andHAC(Fig.9). Weconsidered9.9-37.2µmSpitzer
etal. (2012)concludethatnoneoftheLMCPNeconsidered spectrumandAKARI FIS65/90µmphotometrydata,except
show a dual chemistry, lending more credibility to the idea forthe16-22µmbroadband. Weassumesphericallyshaped
thatthe16–22µmfeatureiscarriedbyacarbon-basedmate- grainswitharadiusofa=0.5µmforAC,SiC,andHACs,and
rial. weexcludedPAHs. Toreproducethebroad30 µmemission
Consideringthegaschemistryaddstotheconfusion.Table usingMgS,asdiscussedinHonyetal.(2003),weconsidered
3showstheCandOgas-phaseabundancesderivedfromthe a continuousdistributionof ellipsoids(CDE, e.g., Bohren&
CELsforsixofthePNewith16–22µmemissionfeaturesdis- Huffman1983;Fabianetal.2001;Minetal.2003)andcalcu-
cussedbyBernard-Salasetal.(2009)andGarcía-Hernández latedQλofCDEMgSusingEq.18givenbyMinetal.(2003).
etal. (2011a). ThreeofthesixareO-richin theirgas-phase Tosimplify,weassumethatthevalueofeachellipsoidMgS
material, while the remaining three MC PNe actually show grainis≃4πa3/3,whereais0.5µm.
a C-rich chemistry. Since the C abundances of SMC1 and The results of the modified blackbody fitting is shown in
SMC6haverelativelylargeuncertainty(0.25dex),thesetwo Fig. 9, and the derived T , m , and mass fraction for each
d,i d,i
SMCPNecouldbeC-rich. Evenwiththisinformation,itre- dustcomponentaresummarizedinTable5.Model1withAC,
mainsunclearwhetherthe16–22µmbumpisduetoanO-rich SiC,andMgScanexplaintheobservedspectrumreasonably
ora C-richcarrier. Thuswe donotassign anyidentification well,whilethemodel2withHACinsteadofMgSpredictsan
tothisfeature,anddonotincludefittingthe16–22µmbump unseen broademission featurearound20 µm. However, we
inouranalysis. should keep in mind that it is extremely difficult to charac-
terizecarboncompoundswithamixedaromaticandaliphatic
2.6.2. 30µmbroadfeature content-suchasHACs-inthelaboratorybecausetheseopti-
calconstantsarestronglyvariablefordifferentchemical and
The carrier of the 30 µm feature remains somewhat of a
physical conditions. Jones (2012) presents HAC theoretical
mystery.WhileMgShasbeenproposedandoftenusedasthe
modelsthatshowtheextremevariabilityofHACspectrade-
carrierofthisfeature(Honyetal.2003),recentworkhascast
pendingonparameterssuchashydrogen-content,grainsize,
doubt on the identification with MgS (see e.g., Zhang et al.
etc. Inanycase, the 20µmfeatureismuchweakerthanthe
2009;García-Hernándezetal. 2010;Zhang& Kwok2011).
30µmfeature(seeGhriskoetal. 2001)andonecoulddetect
Nevertheless,weconsiderMgSasapossibledustcomponent
the30µmfeatureswhilenotdetectingthe20µmfeature. At
inM1-11toexplainthe30µmfeatureinthespectrum.
present, therefore, we do notcompletelyrule outthat HACs
Other potential carriers, in particular hydrogenated amor-
asacarrierofthe30µmbroadfeature.
phous carbon (HAC) (see Grishko et al. 2001; Hony et al.
In this paper, therefore, we assume that SiC and MgS are
2003),shouldalsobeconsidered.IntheSEDmodelforproto-
themaincontributorstothe10–13and30µmbroadfeatures,
PNHD56126,Honyetal.(2003)showedthatbroademission
respectively. In the remainder of our analysis, we will only
featuresaround7-9µmand10-13µmarepartlyduetoHACs,
considerPAHs,SiC,AC,andMgStomodelthedustemission
makingtheidentificationofthe30µmbandwithHACs(Gr-
intheSED.
ishkoetal.2001),a possibility. We examinedwhetherHAC
can be the main contributor to the 10–13 and 30 µm broad
2.6.3. 8.5,17.3,and18.9µmemissionduetoC fullerenes
featuresbyapplyingamodifiedblackbodymodeltotheIRS 60
spectrum,includingbothMgSandHACs. IntheVISIRandSpitzercombinedspectrumofM1-11,we
TheobservedfluxdensityFλduetothermalemissionfrom see infrared features at 8.5 (although blended with the PAH
8 Otsukaetal.
Thelineat8.6µminM1-11canberepresentedbythreeplus
oneGaussiancomponents,as showninFig.10a. We assume
that the profile of the PAH 8.6µm line is represented by the
sum of two Gaussians at the peak wavelengths of ∼8.7 and
∼8.8µm. TheFWHMofthePAH8.6µmrepresentedbythe
sumofthesetwoGaussianis0.2µm,whichisconsistentwith
NGC7027(0.23µminISO/SWSspectrumshowninFig.7).
TheFWHMoftheC 8.5µmlineindicatedbytheblueline
60
is0.17µm. TheFWHM oftheC andPAH complexis0.3
60
µm. TheresultantGaussianfittingforM1-12ispresentedin
Fig.10b. The PAH 8.6µm is representedby the sum of two
Gaussians at ∼8.6 and ∼8.7 µm. The FWHMs of the C
60
andthePAHsforM1-12areassameasthoseofM1-11. The
FIG.9.—Theobserved Spitzer/IRSandVLT/VISIRspectrum ofM1-11 measuredfluxesoftheC 8.5µmandPAH 8.6µm linesin
(graylines) andthe predicted SEDfrommodified blackbody fitting (thick 60
lines).Eachcomponentisindicatedbyathinline.ACstandsforamorphous M1-11arelistedinTable2.
carbon. TheexcitationtemperatureandthenumberofC werede-
60
rivedby creating a vibrationexcitationdiagramas shown in
Fig.10c. WefollowedthemethodofCamietal. (2010).N is
u
TABLE5 the numberof C moleculesin the uppervibrationallevels.
60
RESULTSFROMTHEMODIFIEDBLACKBODYFITTINGTOTHE N iswrittenby
Spitzer/IRSSPECTRUM. u
4πI(C )D2 λ
Models Dust Td md Nu= 60 , (6)
Comp. (K) (M⊙) A hc
model1 SiC 160 2.85(–5) where I(C ) is the fluxes of C lines in erg s- 1 cm- 2, D is
60 60
(Fig.9a) AC 120 2.97(–4) the distance to M1-11 (2.1 kpc; Tajitsu & Tamura 1998), A
MgS 220 3.17(–6)
model2 SiC 170 1.75(–5) are the transition probabilities (4.2, 1.1, 1.9 s- 1 for C60 8.5,
(Fig.9b) AC 120 1.77(–4) 17.3, and 18.9 µm, respectively, from García-Hernández et
HAC 80 0.11 al. 2011b),hisPlanck’sconstant,andcisthespeedoflight.
Thevibrationaldegeneracyisgivenbyg . Inthermalequilib-
u
rium,theBoltzmannequationrelatestheN totheexcitation
8.6µm,seebelow),17.3,and18.9µm,mostlikelyduetothe u
temperatureT :
fullereneC . ext
60
In our own Milky Way Galaxy, these C60 infrared fea- Nu∝guexp(- Eu/kText). (7)
tureswererecentlydetectedinfivePNe,includingTc1,M1-
12, M1-20, K3-54, and M1-60 (Cami et al. 2010; García- Eu and k are the energy of the excited level and the Boltz-
Hernández et al. 2010; García-Hernández et al. 2012), a mannconstant,respectively.Weconfirmedthatourmeasured
C-rich PPN (IRAS01005+7910; Zhang & Kwok 2011), and excitation temperature, Text of 338±9 K in Tc 1 using Eqs.
twoO-richpost-AGBstars(IRAS06338+5333andHD52961; (6)and(7)isconsistentwithCamietal. (2010;332K).Ac-
Gielen et al. 2011). In Fig.8, we show the IRS spectrum cordingly, we obtained Text of 399±36 K and the N(C60) of
of M1-12 in comparison to M1-11. The C60 17.3 and 18.9 4.57±1.23(+46).ThetotalmassofC60 mC60is2.75(–8)M⊙.
µm features seem to be present in M1-11 although they are OurestimatedText,N(C60),andmC60inM1-12are345±35
much weakerthan those in M1-12. The spectrumof M1-12 K,5.30±1.23(+46),and3.18(–8)M⊙,respectively,adopting
shows spectral features due to PAHs, SiC, AC, MgS, and a Dof3.9kpc(Tajitsu& Tamura1998). García-Hernandezet
veryweak16–22µmfeature,whichresemblesthatofM1-11. al. (2010)measuredthe Text in M1-12of546K. Theirmea-
The16–22µmfeatureisnotseeninTc1,M1-20,K3-54,and sured FWHM of C60 8.5 µm is 0.237 µm. The Text discrep-
M1-60. Some other PNe with fullerenes in the Magellanic ancybetweentheirsisduetothedifferencesinthemeasured
Cloudsexhibitthe16–22umfeature(García-Hernándezetal. linefluxofthisline.
2011a;García-Hernándezetal. 2012). Inthe insetofFig.8, 3. RESULTS
the∼16-20µmspectraofM1-11andM1-12withalocaldust
3.1. CELsplasmadiagnostic
continuumsubtracted, are shown. The wavelengthpositions
oftheintensitypeakandthelinewidthsofC60 17.3and18.9 We determined the electron temperatures Te and densities
µm lines in M1-11 are almost coincidentwith those in M1- neusing11diagnosticCELs,andlistedtheresultsinTable7.
12. Inaddition,thecomplexlinearound8.5-8.6µm-which For [NII] λ5755 and [OII]λλ7320/30, we subtracted the
turns out to be a blend of PAH 8.6 µm and C 8.5 µm - in recombinationcontaminationfrombothlinesusing
60
M1-11isverysimilartothatinM1-12,asshowninFig.10.
I ([NII]λ5755) T 0.33 N2+
These comparisonwith M1-12 supportsthe identification of R =3.19 e × , (8)
thisfeatureasaC +PAHblend. I(Hβ) (cid:18)104(cid:19) H+
60
Toquantifytheexcitationtemperatureandthetotalnumber
and
ofC ,weneedtoseparatefluxofC 8.5µmfromthePAH
60 60
8.6µmband. Camietal. (2010)reportedthattheFWHMof I ([OII]λλ7320/30) T 0.44 O2+
C608.5µminthePNTc1is0.15µmbyGaussianfitting.Tc1 R I(Hβ) =9.36(cid:18)10e4(cid:19) × H+ . (9)
showsstrongC linesbutveryweakPAHbands. Assuming
60
thattheFWHMofC 8.5µmis∼0.15µminM1-11andM1- givenbyLiuetal. (2000).AdoptingN2+ andO2+ ionicabun-
60
12, we fit the broadline at 8.6 µm with multiple Gaussians. dancesderivedfromN IIandOIIlines(seeSection3.4),we
ThedetectionofC inthePNM1-11 9
60
FIG.11.—ne-Tediagram. EachcurveislabeledwithanIDnumbergiven
inTable7. Thesolidlinesindicate diagnostic linesoftheTe. Thebroken
linesindicatediagnosticlinesofthene.
TABLE6
FIG.10.—(panels(a)and(b))Theline-profilesofC60at8.5µminM1-11 ADOPTINGneANDTeFORTHECELIONICABUNDANCE
andM1-12(bluelines). Thelocal dustcontinua aresubtracted. Thegray CALCULATIONS.
linesaretheobservations. Wefitthebroadlineat8.6µmbythreeorfour
GThaeusrseidanl.inTehseadreecthoenvsoulmvedofptrhoefisleescoarmepinodniecnattse.dTbhyetheembislasicokna-lnindeblaureoulinndes9. Zone Ions ne(cm- 3) Te(K)
µmis[ArIII]8.99µm.(panel(c))TheexcitationdiagramforC60inM1-11 1 N0,O0 1380 9240
andM1-12. ThefilledandopencirclesaretheobserveddatainM1-11and 2 N+,O+,P+,S+,Cl+ 36490 8410
M1-12,respectively.Thelinesindicatedrepresentthebestfittothedata.See 3 O2+,Ne+,S2+,Cl2+, 51120 9540
textindetail. Ar2+,Fe2+,Kr2+
derivedthatIR([NII]λ5755)=0.12andIR([OII]λλ7320/30) is for ions with 0<IP.13.6 eV (zone 2). ne([SIII]) and
= 2.11. The recombinationcontaminationis ∼2 % in [NII] the averaged temperature among Te([OIII]), Te([SIII]), and
λ5755and∼8%in[OII],respectively. Te([ArIII])isforionswithI.P.=14.4–35.5eV(zone3).
The resulting n –T diagnostic diagram is shown in
e e
Fig. 11. The solid lines indicate diagnostic lines for 3.2. RLplasmadiagnostics
the electron temperatures, while the broken lines are
We calculate the He, C, N, and O abundances using RLs
electron density diagnostics. Since the gas in M1-11
oftheseelementsbyadoptingtheT derivedfromtheBalmer
has much higher density than the critical densities of e
the density sensitive lines [OII] λλ3726/29 and [SII] discontinuity together with HeI line ratios and the ne from
theBalmerdecrements,listedinTable7. TheBalmerdiscon-
λλ6717/31, the ratios of [OII] I(λλ3726/29)/I(λλ7320/30)
tinuitytemperatureT(BJ) was determinedusingthe method
and [SII] I(λλ6717/31)/I(λλ4069/76) are density-sensitive e
describedby Liu et al. (2001), which we used to obtain the
rather than temperature-sensitive. The critical densities
C2+,N2+,andO2+ abundancesfromrecombinationlines.
a∼t98T0e=c1m00- 30,0reKspefcotrive[lOy,IIa]ndλλt3h7o2se6/2o9f [aSreII]∼λ4λ5607017a/n3d1 TheHeI electrontemperaturesTe(HeI)werederivedfrom
are ∼1400 and ∼3600 cm- 3, respectively. The densities theratiosofHeII(λ7281)/I(λ6678),I(λ7281)/I(λ5876),and
I(λ6678)/I(λ5876) assuming a constant electron density of
derived from the [OII] λλ3726/29 and [SII] λλ6717/31 106cm- 3,estimatedfromtheBalmerdecrements(seebelow).
ratios might be the value for thin shell region, while
those from the [OII] I(λλ3726/29)/I(λλ7320/30) and [SII] WeadoptedtheemissivitiesofHeIbyBenjaminetal.(1999).
I(λλ6717/31)/I(λλ4069/76)wouldbethevalueforthebright TheTe(HeI)derivedfromthreedifferentlineratiocombina-
rim.Todeterminen ,weadoptedT=10000Kforalldensity- tionsis3980-6980K.WeadoptedTe(HeI)derivedfromHeI
e e I(λ7281)/I(λ6678)for the He+ abundancecalculations. The
cdmia-g3n,oswtichilcihnesi.s Tthe(e[NaIvIe])rawgeasbceatlwcueleantedneu([sOingII]n)e=d3e6ri4v9ed0 Oretassuoknawethayl.th(i2s0T1e0()H.eI)isthemostreliablewasdiscussedin
fromI(λλ3726/29)/I(λλ7320/30)(ne([OII]n/a)hereafter)and The intensity ratios of the high-orderBalmer lines Hn (n:
ne([SIII]). For Te([SIII]), Te([OIII]), and Te([ArIII]), we the principalquantumnumberof the upperlevel) to a lower
adopted ne([SIII]). For Te([OI]), we adopted ne([NI]). Our Balmer line, e.g., Hβ, are also sensitive to the electron den-
estimatesforTe([NII]),Te([OIII]),andTe([SIII])areinexcel- sity. In Fig. 12, we plot the ratios of higher-order Balmer
lent agreementwith those by Henry et al. (2010), who esti-
lines to Hβ compared to the theoretical values by Storey &
mated10720,9996,and9100K,respectively. Theestimates
Hummer (1995) for T(BJ) and n of 105, 5×105, and 106
forn andT aresummarizedinTable7. e e
e e cm- 3. Theelectrondensityintherecombinationlineemitting
To calculate the CEL ionic abundances, we adopt a three
zone model based on n -T diagram. The T and n combi- regionsseems to be >105 cm. Care when dealing with this
e e e e
nationsforeachionarelistedinTable6. FortheN0 andO0 valueisnecessary,becauseitapparentlyhaslargescatter.
abundances,weadoptedTe([OI])andne([NI])(zone1). The 3.3. CELionicabundances
averagedneisfromne([OII]n/a)andne([SIII]);andTe([NII])
10 Otsukaetal.
TABLE7
PLASMADIAGNOSTICRESULTS.
ID Diagnostic Value Result
Te (1) [NII](λ6548/83)/(λ5755) 42.45±1.14a 8410±90
(K) (2) [OIII](λ4959/5007)/(λ4363) 182.94±20.32 9740±330
(3) [ArIII](λ7135)/(λ5192) 132.44±26.92 10060±780
(4) [OI](λ6300/63)/(λ5577) 74.62±14.31 9240±640
(5) [SIII](λ9069)/(λ6313) 9.96±2.63 8830±980
HeI(λ7281)/(λ6678) 0.20±0.01 6890±330
HeI(λ7281)/(λ5876) 0.052±0.002 5920±230
HeI(λ6678)/(λ5876) 0.26±0.01 3980±160
Average 5600
BJ BalmerJump 5400±1300
ne (6) [NI](λ5198)/(λ5200) 1.63±0.13 1380±350
(cm- 3) (7) [OII](λ3726)/(λ3729) 2.75±0.05 5750±380
(8) [OII](λ3626/29)/(λ7320/30) 3.11±0.10b 21860±780
(9) [SII](λ6716/31)/(λ4069/76) 0.63±0.02 35350±1400
(10) [SIII](λ18.71µm)/(λ9069) 0.44±0.11 51120±15550
(11) [ClIII](λ5517)/(λ5537) 0.40±0.10 22110-63730
Balmerdecrements 105–106
aCorrectedrecombinationcontributionfor[NII]λ5755.
bCorrectedrecombinationcontributionfor[OII]λλ7320/30.
(2008). The discrepancies between our N+, O+, S+ abun-
dancesandtheresultsbyHenryetal.(2010)aremainlydue
toadoptedelectrontemperature;Henryetal.adopted10200
K. Note that they employed three different Ts and a con-
e
stant n =20000 cm- 3 in their models. With their Ts, we
e e
would find N+, O+, and S+ abundances comparable to their
results. Lastly,aminordiscrepancyfortheN+ andO+ abun-
dancesmustbeduetotherecombinationcontaminationinthe
[NII]λ5755and[OII]λλ7320/30lines,respectively.
3.4. RLionicabundances
OurvaluesfortheionicabundancesderivedfromRLsare
listed in Table 9. In general, the Case B assumption applies
tolinesfromlevelshavingthesamespinasthegroundstate,
and the Case A assumption applies to lines of other multi-
plicities. Inthelastofthelineseriesofeachion,wepresent
theadoptedionicabundanceandtheerrorestimatedfromthe
FIG.12.— PlotoftheintensityratioofthehigherorderBalmerlinesto
Hβ (CaseBassumption)withthetheoretical intensityratiosinTe=5400K line intensity-weightedmean. Effectiverecombinationcoef-
anddifferentne. ficients for the lines’ parent multiplet are the same as those
used by Otsuka et al. (2010). The RL ionic abundancesare
The derivedionic abundancesare listed in Table 8. In the insensitive to the electron density under .108 cm- 3 (Zhang
last line of the transition series for each ion, we present the
&Liu2003). Fortheionicabundancecalculations,wethere-
adopted ionic abundance in bold face. The adopted values
fore adoptedthe effective recombinationcoefficientsin case
represent the line intensity weighted mean in case two or
of n =104 cm- 3 for C2+ and N2+. For He+ and O2+ calcula-
more lines are detected. As references, the results by Ster- e
tions, we adopted n =106 cm- 3 and 104 cm- 3, respectively.
ling& Dinerstein(2008,forKr)andHenryetal. (2010,for e
theothers)arealsolisted inthelastcolumn. Thisisthefirst SinceHeII,CIII,CIV,NIII,andOIIIappearedtobeofstel-
time the Ne+, P+, and Fe2+ abundances are derived for M1- larorigin,wedidnotestimatetheabundancesoftheseions.
TheHe+ abundancesaredeterminedusingelectrondensity
11. Intotal,fifteenionicabundancesaredeterminedbysolv-
ing fora >5 levelatomicmodel, with the exceptionofNe+, insensitivesix HeI linesto reduceintensityenhancementby
collisional excitation from the He0 2s 3S level. For the C2+
forwhichtheabundancewascalculatedusingatwolevelen-
abundances,theV6andV17.06lines,whichhavehigheran-
ergy model. We adopted the same collisional strengths and
gular momentum as upper levels, seem to be unaffected by
transitionprobabilitiesusedinOtsukaetal. (2010,2011)ex-
ceptforCl+,forwhichweadoptedthetransitionprobabilities both resonance fluorescence by starlight and recombination
fromtheCHIANTIatomicdatabase9,thecollisionalimpacts fromexcited2S and2D terms. ComparisonoftheC2+ abun-
ofTayal(2004b),andthe levelenergylisted in AtomicLine dances derived from V6 and V17.06 lines indicated that the
List v2.05b12. We subtractedthe recombinationcontamina- observedCII lines would haveless populationenhancement
tion in the [NII]λ5755 and [OII]λλ7320/30 lines to derive mechanisms.OurestimatedHe+andC2+abundancesarecon-
theN+ andO+ abundances. sistentwithHenryetal. (2010;3.56(–2),4.48(–4)).
In general, our derived abundances are comparable to the WeestimatedtheO2+abundancesusingtheOIIlinesshow-
values of Henry et al. (2010) and Sterling & Dinerstein ing the least contaminationfrom otherionic transitions. We
excludedtheOII4676.23ÅlinewhendeterminingO2+abun-
9http://www.ukssdc.ac.uk/solar/chianti/ dance, because this line is much stronger than the other V1