(Abundances),AtmosphericStructure,andtheMassLossProcessinMiras

KenHinkle(NOAO)ThomasLebzelter(Vienna)

OscarStraniero(INAF)

AGB–majormasslossphaseforlowmassstars

AGBmasslossrates~10-6M! yr-1.

WhitedwarfiniPalmasstofinalmassrelaPon–

byendofMiraphase

>0.5M! lost

Weidemann2000AA363647

Whatisthemasslossmechanism?

TextbookmodelofMiraextendedatmosphere

Clearoverallpicturebutmanydetailsremainunkown

Gail&Sedlmayr2014,’PhysicsandChemistyofCircumstellarDustShells,(CambridgeUniv.Press),Chapter16.

ExpandingCircumstellarShell

StellarPulsaDon

Photospheric–CircumstellarconnecDon

Howdoweexploretheinner-circumstellar/extendedphotosphericregion?

•  Masers–Images,especiallySiO

•  Interferometry–near-IR/radiosizesandimages•  IRSpectroscopy

LowexcitaDon2-0COlinesandH2OlinesinMirasareasymmetric

Tsujinamedtheregionprobedbytheselinesthe“MOLsphere”(ApJ540L99)

Tsuji’sworklimitedtonon-variablestars

Hinkle1978,ApJ,220,210

AlongDmeseriesofInfraredobservaDonsoftheS-typeMiraχCygsuggestedaquasi-staDonaryMOLsphere

Filledsymbols=photosphere,opensymbols=MOLsphere

Hinkleetal.1982,ApJ,252,697

Hinkleetal1982

StellarpulsaDonmodels

StaPonaryMOLsphereisatmanyR*

Nowotny,Höfner,&Aringer2010,AA,514A35

3yearvelocityDmeseriesfortheMiraRCas

MovingMOLspherePeriod≠pulsaPonperiod

OpPcalperiod=430days,

solidsymbol=photosphere

opensymbol=MOLsphere

RadiuschangesduetopulsaDon

HighexcitaPonlines–periodicvelocitychanges,1R*

LowexcitaPonlines–aperiodic,>2R*

Nowotny,Höfner,&Aringer2010,AA,514A35

LowexcitaDonlineprofilechangewithDme

Linesusuallyblendedbutoccasionallyseparated—allowsmeasurementofMOLspherelines

CurveofGrowthAnalysis

-15 -14 -13 -12-5

-4.8

-4.6

-4.4

-4.2

-4

R Cas 84 Jun 12EmpiricaldeterminaPonoftemperature

+=planeparallelmodel

1000Kgas=2–3R*

Models–GastemperatureanddustcondensaDonvsradius

"COobservedwouldbeatabout2R*

"DustcondensaPonatabout3R*

(Nowotnyetal.2010,Reid&Menten1997,ApJ,476327)

Interferometry-radiusofthecoolmolecularlayer"2.2R*

FLOUR/IOTA2.2μmobservaPons

(Perrinetal.2004AA426279)

Massoftheshell

•  Curveofgrowthwellfitbyplane-parallelmodel–suggeststhinlayer

•  Assuming:–  Rshell=2Rmira– Rmira=400R!

– Sphericalsymmetry– Solarabundances

•  Mshell=3x10-5M!

Modelsprovidedensity

Nowotnyetal.(2010)

Assumingρ=10-13gcm-2at2R*,logNL(CO)=21.3resultsinashell>1000R!thick.

ThethinnershellsuggestedbytheobservaDonsrequiresdensity10–100xlower.

H2Olinespresent

SimilarvelocitychangestoCObutnotidenPcal

Probesvelocitystructure

1000K–gasconsistslargelyofCOandH2O--abundances

MiraMOLsphere

•  Temperature~1000-1400K•  Density~10-15g/cm3

•  Modelssuggestradius2-4R*,atmosphereextendedbystellarpulsaPon

•  DustcondensaPonzone•  Interferometrysuggestsradius2R*•  MOLspheremass~10-5M•  Timevariable–episodicmassloss

RichphotosphericspectrumintheIR

Isotopiclines:12CO13CO

C16OC17O

C18O

SurfaceisotopicraDosalteredbydredge-ups

2ndand3rddredge-upsdependonmass

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1stdredge-uponRGB.CNOcyclematerialmixedtosurfaceresultsinlargechangesinisotopicraPos.2nddredge-uptakesplaceforstarsofmass>4M☉duringtheearlyAGB.

3rddredge-upduringlateAGB.ProductsofHeburningmixedtosurface.

• Moremixingforstarsundergoingstrongthermalpulses.

• Lowmassstarsdonotexperiencestrongthermalpulses.

• ThermalpulsesarealsoweakerinthemostmassiveAGBstars

• HotBosomburningoccursformassiveAGBstars

Stranieroetal.2006NuclearPhysicsA,777,311

12C/13Cand16O/17OdependoniniDalmass

ModelpredicPonsforsolarcomposiPonareintoppanel

Measuredparametersareinbosompanel.NotesymbolsfordifferentclassesofAGBstars.

Mstarswithlarge16O/17Ohavenotexperienced3rddredge-upandhavemassesbelow1.5M!.

ThesamplewaslimitedtobrightMirasmostlypickedrandomlyfromthefieldsoisdominatedbyoxygenrich(M-type)Miras.

Presolarsiliconcarbidedustgrain-AGBstarmaterialinthelab

• Grainsareisolatedfrommatrixmaterialofmeteorites.• Near-alloxygenrichgrainsoriginateinAGBstarwinds.• Abundancescanbederivedfromthegrains.• TimeCapsule

Image:GailandSedlmayer,PhysicsandChemistryofCircumstellarDustShells2013

Miraandgrainisotopicabundances

1E-5 1E-4 1E-3 0.011E-4

1E-3

0.01

17O/16O

18O/16O

Filledcircles=Miras

Opensquares=grains

Shivtorightresultsfromincreasing17Oand18OabundancesduetogalacPcchemicalevoluPon(GCE)overthelast4Gyr.

AGBstarabundancesarepredictedtopopulatethecentraldenseregion.

ThelargespreadintheMiravaluesinthe18O/16OaxisresultsfromdifficulPesinmeasuringthe18OandinanincreasingspreadofiniPal18OabundancesduetoGCE.