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(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.
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
3yearvelocityDmeseriesfortheMiraRCas
MovingMOLspherePeriod≠pulsaPonperiod
OpPcalperiod=430days,
solidsymbol=photosphere
opensymbol=MOLsphere
RadiuschangesduetopulsaDon
HighexcitaPonlines–periodicvelocitychanges,1R*
LowexcitaPonlines–aperiodic,>2R*
Nowotny,Höfner,Åer2010,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
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.
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