NGC6822 short period variable stars, stellar population and distance scale

Results are presented on a study of the short period variable stars in the dwarf irregular galaxy NGC6822. We observed an almost uniformely populated classical instability strip from the Horizontal Branch up to the Classical Cepheids region. The main goal

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aVariableStarsintheLocalGroupASPConferenceSeries,Vol.2nn,2004D.W.Kurtz&KarenPollard,eds.NGC6822:shortperiodvariablestars,stellarpopulationanddistancescale.LaraBaldacciBolognaUniversity,viaRanzani1,I-40127BolognaLucaRizziINAF-PadovaObservatory,vicolodell’Osservatorio5I-35122PadovaGisellaClementiniINAF-BolognaObservatory,viaRanzani1I-40127BolognaEnricoV.HeldINAF-PadovaObservatory,vicolodell’Osservatorio5I-35122PadovaAbstract.ResultsarepresentedonastudyoftheshortperiodvariablestarsinthedwarfirregulargalaxyNGC6822.Weobservedanalmostuni-formelypopulatedclassicalinstabilitystripfromtheHorizontalBranchuptotheClassicalCepheidsregion.Themaingoalweachievedfromtheanalysisofthefaintsampleisthe rstdetectionofRRLyraestarsinthisgalaxy.1.IntroductionTheaimofthepresentprojectisthestudyofthedwarfirregular(dI)galaxyNGC6822usingitspulsatingvariablestarcontent.Pulsatingvariablesaretrac-

ersofdi erentstellarpopulationingalaxiesandusefulfortestingtheoreticalmodels.Moreover,someofthem,suchastheRRLyraestarsandtheClassicalCepheids,areprimarydistanceindicatorsintheLocalGroup.

2.Observationandanalysis

Time-seriesimagingofNGC6822wasobtainedattheVLT(36Vand11Bim-ages)in2001August.PhotometricreductionswereperformedusingDAOPHOTandALLFRAME(Stetson1994)andthecandidatevariableswereidenti edus-ingISIS2.1(Alard2000).About450bona decandidatevariablesweredetected,andallarebeinganalysedwithGRATIS(GRaphycalAnalyzerofTImeSeries,seeClementinietal.2000)inordertochecktheiractualvariation,toclassifythemandtodeterminetheirpulsationalcharacteristics.

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