Populations of AGB stars and LPVs in the Galaxy and Local Group

In this review I will discuss recent developments on the topic of resolved Asymptotic Giant Branch (AGB) stars and Long Period Variables (LPVs) in our Galaxy, the Magellanic Clouds, and the Local Group in general. Since the main characteristics of AGB star

5

2

n

Ju

6

1

1

v

18

3

6

5

/

h

p

-

o

rt

sa

:v

i

X

r

aResolvedStellarPopulationsASPConferenceSeries,Vol.TBA,2005D.Valls–Gabaud&M.Chavez(eds)PopulationsofAGBstarsandLPVsintheGalaxyandLocalGroupM.A.T.GroenewegenInstituutvoorSterrenkundeCelestijnenlaan200BB-3001Leuven,BelgiumAbstract.InthisreviewIwilldiscussrecentdevelopmentsonthetopicofresolvedAsymptoticGiantBranch(AGB)starsandLongPeriodVariables(LPVs)inourGalaxy,theMagellanicClouds,andtheLocalGroupingeneral.SincethemaincharacteristicsofAGBstarsare(1)theirinfrared,(2)pulsationaland(3)chemicalproperties,itis ttingthatIwillfocusonrecentresultsfromthe(a)2MASS/DENISandMSXnear-andmid-IRsurveys,the(b)micro-lensingsurveysand(c)dedicatednarrow-bandimagingsurveys.Thepresentationisavailableatdoc.xuehai.net～groen1.IntroductionAllmain-sequencestarsbornwithmassesbelow<～8M⊙haveorwillgothroughtheevolutionaryphasecalledAsymptoticGiantBranch(AGB).ThelowerlimitininitialmassissetbytheageoftheGalacticDisc,theupperlimitissetbythemasswherecarboncanbeignitedinthestellarcore.TheAGBisthe nalphasewhereintermediate-massstarshavenuclearburningintheformofalternateHydrogenandHeliumshellburning,beforetheycrosstheHerzsprung-RusselldiagramtobecomePlanetaryNebulaeandthenWhiteDwarfs.AsummaryoftheinteriorstructureandstellarevolutionuptoandontheAGBcanbefoundintherecenttextbook“AsymptoticGiantBranchStars”(Habing&Olo son2004).

AGBstarsareluminous([～0.1–afew]104L⊙)andcool,withe ectivetemperaturesintherange3850to～2500K(forM0toM10giants,e.g.Fluksetal.1994).FromthisitfollowsthatAGBstarsarebig(uptoafewhundredR⊙),andcombiningthiswiththeclassicalpulsationequation1P=QR1.5M 0.5itfollowsthatanyradialpulsationsthatwouldoccurwouldhaveperiodsbetweentensandhundredsofdays.

Equallyimportant,andtypicalfortheAGB,arethechemicalpeculiaritiesthatoccurduringthisevolutionaryphase(seeChapter2intheabovementionedbook).Dependinginacomplexwayoninitialmass,metallicity,mass-loss,mixingandburningintheenvelope[hotbottom-burning],anAGBstarmaygothroughseveralthirddredge-upeventswherebymainlycarbon,nitrogen,oxygenands-processelementsaremixedultimatelyintothestellarphotosphere.

第1页下一页