ZhangYongTheUniversityofHongKong

Moleculesinplanetarynebulae

“”Blowing inthewind”conferenceVietnam,Aug,2016

Outline

• Introduction

• Gas-phasemoleculesinplanetarynebulae

• Aromatic/aliphaticmaterials

• C60 andfullerene-relatedcompounds

Proto-planetarynebula

Introduction:

PNe containkeyinformationforthematerialrecyclingbetweenthestarandISM.

Dustandvariousmoleculesareformed.

Nucleosynthesis productsaredredged-upfromstellarinteriortosurface,andareejectedintospace.

Expanding into the ISM

FurtherprocessedbyUVradiation.

106yr

103yr104yr

Materiallifecycle

PN PPN

AGB

Circumstellar chemistry(AGB)

Dustformation（1000K;1010cm-3）

InterstellarUVradiation

Low-densityregions（~30K;105cm-3）

stellarwindacceleration

C/O:• 3rddredge-up• HBB C/O<1

Silicates…

C/O>1SiC…

DenseregionsParentmolecules Daughtermolecules

Chemicaldrivers:• InterstellarUVradiationfields:

• induceion-neutral chemistryJ• Shocks:

• endothermic reactionsJ• sputterandshatterdustJL• dissociatemoleculesL

• Dustgrains:• InducegrainsurfacereactionsJ• shieldUVradiationfieldL

Circumstellar envelopeatthePNstage

Ionizedregion（~104K;103cm-3）

PDR (6eV<hv <13.6eV)>35,000K

UV,SoftX-ray

H,C,C+,HCO+…

Dustandmolecularenvelope;AGBremnant

H+,He+,O2+…

contaminatetheISM

Hostileenvironments:Photo-dissociation (increasingradiationfield);dissociativerecombination(abundante-)

Survivalofmolecules:Opticallythickclumpsandcentraltorus;self- andmutual-shieldingofCOandH2

Zhangetal.2012~103K~105cm-3

(Ionization-bounded)

• Heating by e- rejection from grains• High-density shell of shocked winds• Electrons are provided by

C0 !"$% e + C+

H0 &'()* e + H+

(e.g.Zhangetal.2008,2009a,2009b,2012)

MolecularlinesurveysatmmtowardsAGB,PPNandPNenvelopes

CN

ChemicalevolutionofC-richcircumstellar envelopes

• During the AGB-PPN transition, longC-chain molecules are enhanced. Si-and S-bearing molecules aredepleted.

• In the PN stage, manymolecules aredestructed by UV radiations. Someionized species and radicals areenhanced.

Lineintensityratios PPN/AGB

LogCR

L2688/IRC+10216

AGB/AGB

PN/PPN

ChemicalcompositionsaresignificantlyalteredduringtheAGB-PPN-PNtransitions.

(Zhangetal.2012)

~103 yr

Chemicalmodelsofplanetarynebulae• Black (1978,1983) predicted the presence of H2, H2

+, HeH+(non-detection; Moorhead et al. 1998; Liu et al. 1997), OH,CO+, and CH+ .

• The models of dense globules in PNe suggest detectable C2H and CN emission, but too low HCO+ abundance (Howeet al. 1994).

• The effects of shocks and soft X rays were considered in the time-dependent models of Natta & Hollenbach (1998).

• To explain the CH+, OH, and CH lines observed in NGC 7027, Yan et al. (1999) and Hasegawa et al. (2000) constructedsteady-statemodels composed of a thin-dense shell and an extended region.

• Ali et al. (2001) modeled the chemistry of cool (~15K) clumpy nebulae, and predicted high abundance of CH, CH2,CH2

+, HCl, OH, and H2O. But the calculated CS and SiO abundances are too high.

• The clumpy models of Redman et al. (2003) can predict the survival of short-chain molecules in young PNe, butsignificantly underestimatemolecular abundance in evolved PNe.

• Kimura et al. (2012) constructed models to study the effect of stellar and nebular properties on molecularcomposition. The observed HCN/HNC ratios cannot be reproduced.

2atoms

3atoms

4atoms

5atoms

6atoms

7atoms

8atoms

9atoms

10atoms

11atoms

12atoms

>12atoms

H2 AlFAlCl C2CH CH+

CNCOCO+ CPSiCHClKCl NHNO NSNaClOHPNSO SO+

SiN SiOSiS CSHF HDFeO?O2 CF+SiH?POAlOOH+ CN-

SH+ SHHCl+TiOArH+

NO+?

C3 C2HC2OC2SCH2 HCNHCOHCO+

HCS+ HOC+H2O H2SHNCHNOMgCNMgNCN2H+ N2ONaCN OCSSO2 SiC2CO2 NH2H3

+ SiCNAlNC SiNCHCP CCPAlOH H2O+

H2Cl+KCNFeCN HO2

TiO2 C2NSi2C

c-C3H l-C3HC3N C3O C3SC2H2 NH3HCCNHCNH+

HNCOHNCSHOCO+

H2COH2CNH2CS H3O+

c-SiC3 CH3C3N- PH3HCNOHOCNHSCNH2O2C3H+

HMgNCHCCO

C5 C4H C4Sil-C3H2c-C3H2H2CCN CH4

HC3NHC2NCHCOOHH2CNHH2C2OH2NCNHNC3 SiH4

H2COH+

C4H-

CNCHOHNCNHCH3ONH4

+

H2NCO+?NCCNH+

C5Hl-H2C4C2H4CH3CNCH3NCCH3OHCH3SHHC3NH+

HC2CHONH2CHOC5Nl-HC4Hi-HC4Nc-H2C3OH2CCNH?C5N-

HNCHCN

C6HCH2CHCNCH3C2HHC5NCH3CHOCH3NH2

C2H4OH2CCHOHC6H-

CH3NCO

CH3C3NHCOOCH3CH3COOHC7H C6H2

CH2OHCHOl-HC6HCH2CHCHO?CH2CCHCNH2NCH2CNCH3CHNH

CH3C4HCH3CH2CN(CH3)2OCH3CH2OHHC7NC8H CH3CONH2

C8H-

C3H6CH3CH2SH?

CH3C5N(CH3)2CO(CH2OH)2CH3CH2CHOCH3CHCH2O

HC9NCH3C6HC2H5OCHOCH3OCOCH3?

c-C6H6

n-C3H7CNi-C3H7CNC2H5OCH3?

HC11NC60C70C60+

Moleculesintheinterstellarandcircumstellar environments

Moleculesdetectedin:ISM(only)EnvelopesaroundevolvedstarsPlanetarynebulae

195moleculesareidentified(ortentativelyidentified)inspace,amongwhich107aredetectedincircumstellar envelopesofevolvedstars(VYCma,OH231.8+4.2,IRC+10420,IRC+10216,CRL618,CRL2688, NGC7027,Tc1,etc.).Morethan20moleculesaredetectedtowardsPNe.

Complexaromaticaliphaticmolecules

(ref.CDMSetc.)

11/28/41

8/26/39

2/15/272/13/23 8/17

5/10 2/113/10

0/51/4 1/4 3/4/4

Sensitive observations atlowfrequency arerequiredtorevealtherotationtransitionsfromcomplexmolecules inPNe.

H2 andCO• > 70 PNe are detected in H2.

vH2 emission is stronger in, but not limited to, bipolar PNe with equatorial rings (Marguez-Lugo et al. 2013, 2015 and references therein).

vH2 emission in the torus is clumpy and filamentary, but not uniform (Manchado et al. 2015). vCan H2 be formed again on dust grains after the central star has entered the cooling track? (an observational

evidence provided by Herschel; van Hoof et al. 2010).vH2 in low-ionization structures may be excited by shocks (Akras et al. 2016).

• ~100 PNe are detected in CO (36% detection rate for young PNe, Huggins et al. 2005). Molecular mass measured from CO decreases with PN ages (1-0.01Msun; Bujarrabal 2006).

Contour: CO envelope of NGC7027 (Nakashima et al.2010)

v The CO/H2 ratio does not significantly vary during the PN stage (Edwards et al. 2014).

IRC+10216(AGB):CO/H2 =8e-4

Helix(evolvedPN):CO/H2 =0.3-6e-4

OHandH2O

• OH and H2O masers probably trace very young O-rich PNe ( < 100—1000 yr). v Confirmed sources: 5 H2O-PNe (Gomez et al. 2015) and 7 OH-PNe (Uscanga et al. 2012; Qiao et al.

2016), among which only two, K3-35 and I16333 show both OH and H2O masers.v The first “water fountain” (youngest) PN, I15103 (Gomez et al. 2015).

• Crystalline water ice has been detected in O- (Molster et al. 2001) and C-rich PNe (Cohen et al. 1999) → Transition from O- to C-rich outflow following a helium flash?

• OH and o-/p-H2O have been detected in the C- and O-rich PNe by ISO (Liu et al. 1997) and Herschel (Wesson et al. 2010; Bujarrabal et al. 2012).v Abundant H2O in the inner shells of NGC7027 suggests an ongoing process producing water

(Santander-Garcia et al. 2012).

Hydroxylradical Water

• Observations show that the intensity of CO+ line in PNe is positively correlated with that of HCO+

(Bell et al. 2007).

• The routes, O+,- OH+ and CO

+,- HCO+, can be ruled out in PDR because of high dissociative recombination of H/0 in the presence of e- (except in young PNe where H/0 is enhanced by x-ray).

HCO+,CO+,andOH+

Chemistry in PDRs: CO $%

O +0

O++1 OH+

+1 H2O++1 H3O+

2'

→ OH 40

→ CO+ +1 HCO+

• Observations show that HCO+ is a common constituent in molecule-rich PNe, and its abundance keep constant during PN evolution (Edwards et al. 2014, Schmidt & Ziurys 2016).

• For the first time, OH+ was discovered in 5 PNe(including young and evolved PNe) by Herschel (Aleman 2014; Etxaluze et al. 2014).

PNAge(year)

HCO+ /H 2

(10-8 )

DatafromSchmidt&Ziurys (2016)

CRL2688(PPN):HCO+/H2 ~10-9

PN

COhv,H+

CHandCH+

• CHandCH+werediscoveredinNGC7027(Liuetal.1997;Cericharo etal.2010;Wesson

etal.2010).

v TheexcitationanalysisofCH+ linessuggestsTk =300-500Kandn(H2)~107cm-3(Cericharo etal.2010).

v AnewmodelofCH+ excitationsuggestsn(H2)~105cm-3 (Godard&Cernicharo 2013).

Endothermic reaction with an activation energy of 4300K:

0.4eV + C++1 CH+

+1

CH2+2'

→ CH

(inducedbyshocksorvibrationally excitedH2* ).

N-bearingmolecules

ObservedHCN/H2

Figure fromSchmidt&Ziurys (2016)

ModeledHCN/H2inclumps

HCNabundanceskeepapproximatelyconstantduringPNevolution, incontrasttothemodelprediction.

• HCN and CN are common in molecule-rich PNe. Photodissociation ofHCN may explain the high CN/HCN.

• The chemistry HNC is similar to that of HCN. Models cannot reproducethe observed low HNC/HCN ratio in NGC 7027 (<0.06). More sensitiveHNC survey in PNe is required.

• HC3N was discovered only in NGC7027 with an abundance of 10 timeslower than in IRC+10216 (Zhang et al. 2008).

• NH3 has been detected in NGC6302 (Bujarrabal et al. 2011).

• N2H+ was detected only in NGC7027, but with abnormally highabundance (Josselin & Bachiller 2003; Zhang et al. 2008).→ The density

of H3+ is increased byX-ray from the hot center (N2

H3+N2H+).

HCO+

HCN/H2vsPNage

Si- andS-bearingmolecules

• SiO, SO andSO2 arefoundinaPNM2-28(Edwards&Ziurys 2014),indicatingO-richenvironments.

• HCS+ wastentativelydetectedinNGC7027(Hasegawa&Kwok,2001;Zhangetal.2008).

• CS isabundantinC-richAGBandPPN(CS/H2 ~10-6),butabsentinPNe (Bachilleretal.1997).

• CS was discovered in 5 PNe with C/O≤1. → Sulfer in grains is released into the gas phase in oxidation environments? (Edwards et al. 2014).

CS/H

2

CRL2688(PPN):CS/H2 ~10-6

O-richPN

C2H,c-C3H2, andH2COEthynyl radical

Formaldehyde

• C2H, c-C3H2, and H2CO were detected in young and evolved PNe, NGC 7027 and Helix

nebula (Tenenbaum et al. 2009).

• Is C2H from AGB remnant (photodissociation of C2H2) or in situ formed in PDR?

• High c-C3H2 abundance cannot be reproduced by gas-phase chemistry model. It might be

produced by photodestruction of large aromatic compounds (Fuente et al. 2003).

Cyclopropenylidene

MoresensitivelinesurveyscontinuetorevealnewmoleculesinPNe.

Detectedmoleculesinanevolutionarysequence

C-richAGB:~80molecules

C-richPPNe:~40molecules;C60;complexaromaticmolecules

PNe:~20simplemolecules;C60,C70,C60

+;complexaromaticmolecules

Simplemolecules:atomicnumber<6

Diffuseclouds:~20simplemolecules;complexaromaticmolecules;5diffuseinterstellarbandsfromC60

+

PNe havesimilarmolecularcompositionswithdiffuseclouds.(e.g.papersbyZiurys’group)

SeeCernicharo etal.(2011)forareviewofthedetectedmoleculesduringtheAGB-PPN-PNtransitions.

106yr

103yr

104yr

TheunidentifiedInfraredEmission (UIE)

Wavelength (um)

Aromatic(sp2 bonded)• 3.3um,6.2um,7.7um,8.6um,10-

15umfeatures

UIEisdetectedinPNe.ThepresenceofUIEisnotsensitivetotheexcitationclassofPNe.

Aliphatic(sp3 bonded):• 3.4um,6.9umfeatures• 8um,12um,and17umplateaus

UIEcarrier?Proposedcandidates:complexcarbonaceousmolecules• HydrogenatedAmorphous Carbon(HAC)• QuenchedCarbonComposites (QCC)• PolycyclicAromaticHydrocarbons (PAH)• Nanodiamonds• Rydbergmatter

PAHs:

Or MAONs (Mixed aromatic-aliphatic organic nanoparticles; Kwok & Zhang 2011, Nature)?

UIEhasbeencommonlyobserved inproto-PNe (Aro/Aliratioincreasesduring thePPN-to-PNtransition).

InO-richPNe,UIEcarriercanbeformed in-situinPDRs(Guzman-Ramirezetal.2014;Coxetal.2016,posterp.27).

C60 (Buckminsterfullerene,Buckyball)

• Fullerenes (C2n+20) are molecules composed entirely of carbon,in the form of a hollow cage.

• The most famous fullerene is C60, which is arranged as 12pentagons (5-carbon ring) and 20 hexagons(6-carbon ring).

• C60 is highly symmetric (only four IR-activemodes.)

• C60 is physically stable because it is the smallest cage withisolated pentagons (C70 is the second smallestone).

• C60 is chemically active.C60

7Å

10Åπ-electroncloud

1.45Å[5,6] 1.38Å[6,6]

ThediscoveryofC60 inlaboratoryC60 was discovered experimentally forthefirsttimebyKroto etal.(1985,Nature318,162).

Laboratoryexperimentsdesignedtosimulatethegas-phasereactionsIncarbonstaroutflows.

Kroto etal.(1985)

IRabsorptionspectraofC60

7.0μm8.5μm

18.9μm

17.4μm

• Krätschmer etal.(1990)developed newtechniquetoeffectivelyproducesolid stateC60 inlaboratory.

FullerenesintheEarthandmeteorites

• Carbon-richPre-CambrianrockfromRussia(Buseck etal.

1992).

• Allendemeteorite(Beckeretal.1994).

• Shock-producedbreccias oftheSudburyimpactstructurein

Ontario,Canada(Beckeretal.1994).

• ThegeologicalstrataoftheCretaceousy-Tertiaryandthe

Permian-Trassicboundarylayers,associatedwithbolide

impacts(Beckeretal.2000,2001).

• ……

C60andC70havebeenidentifiedin:

Fullerene-like structuresintheAllendemeteorite(Harrisetal.2000)

C60canbeformedinnature.

Searchforfullerenesinspace-- failureexamples

• Snow&Seab (1989)didnotdetectC60inseveralreddenedstars.

• Herbig (2000)didnotdetectC60featuresat3857and3980Åinthespectra

ofO-typestars.

• Sassara etal.(2001)examinedafewobjectsconsideredaspossible sitesof

C60,butdidnotgetpositivedetection.

ElectronictransitionsofC60

VibrationaltransitionsofC60

• UncertaindetectionsinIRC+10216andI07134byClayton(1995)and

Kwoketal.(1999)

• Moutou etal.(1999)didnotdetectC60andC60+intheISO spectrumof

NGC7023(areflectionnebula).

Visible-ultravioletabsorptionspectraof C60.

Theopticalspectrumisdominatedbyabandat404nmwithafewsub-featuresat500-630nm.

Searchforfullerenesinspace-- C60+ asacarrierofDIBs

• C60 hasanionizationpotentialof7.6eV,andispossiblypresentasC60+.

• TheelectronictransitionsofC60+ areinthenear-IR.

Foing & Ehrenfreund (1994, 1997) found that the two near-IR DIBshave wavelengths close to those of C60

+measured in a neon matrix.

ThiswasrecentlyconfirmedbyCampbelletal.(2015;agreementsinwavelengths,intensities,andwidths)

Laboratory spectra of C60+ also reveal weaker bands at 9633, 9578,and 9349A, which were soon detected in DIBs by Walker et al. (2015)and Campbell et al. (2016) using CFHT.

C60+asthefirstidentificationofoneoftheDIBcarriers(Five DIBshavebeenidentified.)

C60+9580 C60+9642

DIB

Gas-phase laboratoryspectraofC60+

Wavelengthsinmatrix

SearchforIRvibrationalmodesofC60-- Thefirstconvincingcase

VibrationaltransitionsofC60 andC70wereforthefirsttimedetectedinayoungplanetarynebulaTc1bySpitzer Telescope (Cami etal.2010,Science,329,1180).

PredictedC60 andC70spectrabythermalmodel

Continuum-subtractedSpitzerspectrumofTc1

(Cami etal.2010)

C60 inmoreobjects

• PlanetarynebulaewithAIBs(GarcÍa-Hernándezetal.2010)• Planetarynebulae intheMagellanic Clouds(GarcÍa-Hernándezetal.2011)• Aproto-planetarynebula(Zhang&Kwok,2011)• Post-AGBstars(Gielenetal.2011,Robertsetal.2012)• ModeratelyH-deficientRCBstars(GarcÍa-Hernándezetal.2011)• ApeculiarbinaryXXOph (Evansetal.2012)……

Circumstellarenvelopessurroundingevolvedstars:

ISMsandPre-mainsequencestars:

• Tworeflectionnebulae(Sellgren etal.2010)• Orionnebula (Rubinetal.2011)• YoungstellarobjectsandaHerbig Ae/Bestar(Robertsetal.2012)

VibrationaltransitionsofC60+ aredetectedininsomeoftheC60 sources.

(Berneetal.2013;Strelnikov etal.2012,2015;)

C60inPNe

C60 hasbeendetectedin11GalacticPNe,4LMC

PNe and7SMCPNe.Thedetectionrateincreases

withdecreasingmetallicity (5%intheMilkyway,

20%intheLMC,and44%intheSMC).(GarcÍa-

Hernándezetal.2012;Otsukaetal.2016)

C60inaproto-planetarynebula-- ProducerofDIBcarrier?

Wavelength(μm)

C607.0μm

C608.5μm

C6017.4μm

C6018.9μm

Zhang&Kwok,2011

C60+ isenhancedinIRAS01005+7910(Iglesias-Groth &Esposito,2013).

→ Circumstellar envelops can produce DIB carrier.

TwoopticalDIBsareenhancedinC60-containingPNe (Diaz-Luisetal.2015).→ C60 derivatives might be DIB carrier.

IRAS01005+7910

C60 canbeefficientlyincircumstellar envelopeswithatimescaleofabout1000years.

Searchforfullerene-relatedcompoundsinPNe

C60Hm&C60Hm+

Cataldo etal.

Na@C60(Dunketal.2013)

CO@C60H2@C60

fullerene compounds DIBs

Physically stable ubiquitous

Chemically active various

Fullerenecompounds asDIBcarrier?

Interstellar fullerene compounds&DIBs(Omont, 2016)

Fullerane (C60Hm)

Intensities of the 4 IR transitions decrease with increasinghydrogenations. à When C60 is heavily hydrogenated, the4 IR transitions are hardly discovered.

I01005

C60

C60H2

C60H4

C60H6

C60H36

Theoreticalspectra(B2LYP/BH&HLYP)

Zhangetal2016

Fullerane wastentativelydiscoveredinaPPN.(Zhang&Kwok 2013)

However, Diaz-Luis et al.(2016) did not detect theCH stretching mode fromfullerane in two strongC60-PNe, TC1 andM1-20.

C60 canbereadilyhydrogenatedwhenmixedwithHatoms.

ExcitationofC60 IRbands:modelsvs. observations

Brieva etal.2016

Fluorescence/thermalmodel

The observed intensity ratios of C60 cannot be reproduced byfluorescence and thermal models (also see Bernard-Salas et al. 2012;Zhang & Kwok 2013).

Possiblecausesforthediscrepancy:• Uncertainintrinsicstrengths• Uncertainmeasurements• Otherexcitationmechanisms

Orhydrogenation ofC60 ?

ExcitationofC60 IRbands:modelsvs. observations

Brieva etal.2016

Fluorescence/thermalmodel

The observed intensity ratios of C60 cannot be reproduced byfluorescence and thermal models (also see Bernard-Salas et al. 2012;Zhang & Kwok 2013).

CalculatedintensityratiosofC60Hm bands

C60+→ C60Hm

6%C60 +H2

HydrogenationcanaffecttheintensityratiosoftheC60-cagevibrationalbands.

observationsobservations

observations

FormationofcircumstellarC60:bottom-upvs.top-down• Collisionsofsmallcarbonclusters(bottom-up):

− Hydrogen-poorenvironmentsatnormaltemperature.

− Hydrogen-richathigh-temperature(>3500K).

• DehydrogenationofHACorPAH(top-down):

− UVphoton-induced.

C60Cchains

PAHDehydrogenation LostofC LostofC

C60HAC

LostofH LostofH

(Berne&Tielens2012)

(GarcÍa-Hernándezetal.2010;Micelotta eta.2012)

EjectionofC2 byreleasingexcessenergy

Aliphatic/aromaticorganicsastheprecursoroffullerene?

3Dstructure

Carrieroftheextinctionbumpat2175A(Iglesias- Groth etal.2003)?

MostoftheC60sources exhibitplateauemission. (GarcÍa-Hernándezetal.2012;Zhang&Kwok2013;Otsukaetal.2013)

Asimilarroute withthatpresented byMicelota etal.(2012)

Strongplateausat8and12umfromaliphaticcomponents

Summary• MolecularcomponentisimportantinPNe.• LargemoleculescansurviveorformduringthePNevolution.• ThechemistryinthePNstageisstillfarfromwellunderstood.• ThecompoundsblownfromPNe aredispersedintotheISM,andarepossiblyrelatedtotheDIBphenomenon(e.g.C60&C60+).

• C60andC70havebeendetectedinPNe,buttheirexcitationandformationmechanismsareunclear.

Future:• SensitivesurveysofmoleculesinPNe arerequiredtoinvestigatecircumstellar chemistry

andcomparewiththemoleculesobservedindiffuseISM.• Itisworthot Searchforfullerene-relatedcompounds(e.g.C60Hm)tostudytheDIB

phenomenon.

ThanksforListening!