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1、Stars,GasandDustinGalaxies8ASPConferenceSeries,Vol.3×10,2000D.Alloin,G.Galaz&K.Olsen,eds.Thestarformationhistoryofresolvedgalaxies:CompositeH-Rdiagram.CarmeGallartAndesFellow.AstronomyDept.YaleUniversity.P.O.Box208101.NewHaven,CT06520-8101,USAandDepartamentodeAstronom´ıa,UniversidaddeChile.Casilla36
2、-D.LasCondes.Santiago.ChileAbstract.Idiscusstheinformationprovidedbycolor-magnitudedi-agramsofdifferentabsolutemagnitudelimitsinthestudyofthestarformationhistoriesofnearbygalaxies.Ireviewtherecentprogressmadeinthefield,withemphasisontheresultsforLocalGroupdwarfgalaxies.1.IntroductionWecanstudytheevolu
3、tionofthenearestgalaxiesinexquisitedetailfromtheinformationcontainedintheH-Rdiagram-orColor-MagnitudeDiagram,CMD-oftheirresolvedstars.Fromit,itispossibletoretrievethestarformationandchemicalenrichmenthistories(SFHandZ(t)),withalevelofdetailthatmainlydependsonthemagnitudelimitoftheavailableCMD.ForCMD
4、sreachingtheoldestmain-sequence(MS)turnoffs,itispossibletobreaktheage-metallicitydegeneracythataffectsmostmethodsofretrievingSFHs.EvenifwecanpursuethiskindofstudyonlyinaverylimitedvolumeoftheUniverse,itisaworthwhiletask,keytounderstandgalaxyformationandevolutioningeneral,because:•Inourneighborhood,weh
5、averepresentativesofalmostanykindofgalax-iesintheUniverse:intheLocalGrouptherearethreespirals,andalargenumberofdwarf-bothdIranddSph-galaxies;thenearestgE,NGC5128isatarXiv:astro-ph/0007239v117Jul2000≃4.0Mpc,andsimilarly,thenearestBCDandLSBgalaxiesareintheM81group,alsoat≃4.0Mpc.Inaddition,bystudyingth
6、edetailsoftheSFHsinthenearestgalaxies,wemaybeabletoidentifytheevolvedcounterpartsofdistantobjectsthatareexperiencingcharacteristicstarformingepisodes.•Thiskindofstudyprovidesdetailedinformationonthefirsteventsofstarformationinthenearestgalaxies.Therefore,wecanaddressquestionslike“havetheoldeststarsin
7、galaxiesallthesameage?”or,“aretheredifferences,intheepochorstrengthoftheearlystarformation,dependingonenvironment”.•Wecantestthehypothesisofgalaxiesbeingassembledbymergingthroughthealmostdirectobservat
