Search for pulsating PMS stars in NGC 6383

A search for pulsating pre-main sequence (PMS) stars was performed in the young open cluster NGC 6383 using CCD time series photometry in Johnson B & V filters. With an age of only ~1.7 million years all cluster members later than spectral type A0 have not

Mon.Not.R.Astron.Soc.000,(2005)Printed5February2008

A(MNLTEXstyle lev2.2)

Searchforpulsatingpre-mainsequencestarsinNGC6383

1211

K.Zwintz ,M.Marconi,P.Reegen,W.W.Weiss1

2Osservatorio

DepartmentofAstronomy,UniversityofVienna,T¨urkenschanzstraße17,A-1180Vienna,Austria

AstronomicodiCapodimonte,ViaMoiariello16,80131Napoli,Italy

arXiv:astro-ph/0501210v1 12 Jan 2005

Accepted.Received;inoriginalform

ABSTRACT

Asearchforpulsatingpre-mainsequence(PMS)starswasperformedintheyoungopenclusterNGC6383usingCCDtimeseriesphotometryinJohnsonB&V lters.Withanageofonly～1.7millionyearsallclustermemberslaterthanspectraltypeA0havenotreachedtheZAMSyet,hencebeingidealcandidatesforinvestigatingPMSpulsationamongAandFtypestars.Intotal286starshavebeenanalyzedusingclassicalFouriertechniques.Fromaboutadozenofstarswithintheboundariesoftheclassicalinstabilitystrip,twostarswerefoundtopulsate:NGC6383#170,with vefrequenciessimultaneously,andNGC6383#198,withasinglefrequency.Inaddition,NGC6383#152isasuspectedPMSvariablestar,butourdataremaininconclusive.Linear,non-adiabaticmodelsassumingPMSevolutionaryphaseandpurelyradialpulsationwerecalculatedforthetwonewPMSpulsators.NGC6383#170appearstopulsateradiallyinthirdand fthovertones,whiletheotherthreefrequenciesseemtobeofnon-radialnature.NGC6383#198pulsatesmonoperiodically,mostprobablyinthethirdradialovertone.

MagnitudesandB Vcolourswereavailableintheliteratureforonlyonethirdofallstarsandweusedthemforcalibratingtheremaining.

Keywords:techniques:photometric,stars:pre-mainsequence,stars:variables:δScuti,galaxy:openclustersandassociations:NGC6383

1INTRODUCTION

Thestudyofthe rststagesintheformationofstarsisoneofthecurrentlymostactiveresearch eldsinstellarastronomy.Pre-mainsequence(PMS)starsliebetweenthebirthlineandthezero-agemainsequence(ZAMS)intheHertzsprung-Russell(HR)diagram.Theyareoftencharacterizedbyahighdegreeofactivity,strongnear-orfar-IRexcessesand–inmostcases–emissionlines.Theyshowphotometricandspectroscopicvariabilityontimescalesofminutestoyears,indicatingthatstellaractivitybeginsintheearliestphasesofstellarevolution.DuringthecontractiontowardsthemainsequenceintermediatemassPMSstarspossesstemperaturesandluminositiessimilartoevolvedstarsintheclassicalin-stabilitystrip.Thisfactsuggeststhatatleastpartoftheiractivityisduetostellarpulsation.

TheexistenceofpulsatingPMSstarswas rstsuggestedbyBreger(1972),whodiscoveredintheyoungopenclus-terNGC2264δScuti-likepulsationintwoPMSstars.Sub-sequentobservationsrevealedsimilaroscillationsinseveral1995),aswellasinPMSmembersoftheyoungopenclus-terNGC6823(Pigulski,Kolackowski&Kopacki2000).AllknownPMSpulsatorspopulatethespectralrangebetweenA2andF5,theirperiodsliebetween18minutes(Amadoetal.2004)andseveralhours,andtheiramplitudesareatmillimagnitudelevel.

Theevolutionarytracksforpre-andpostmainsequencestarsintersectsuchthatstarsoffundamentallydi erentevo-lutionarystatehavethesamee ectivetemperatureandlu-minosity(Breger&Pamyatnykh1998).Hence,thedetermi-nationoftheevolutionarystateofa eldstarmaybeam-biguous.Therefore,youngopenclustersaremostsuitabletosearchforpulsatingPMSstars.

2THEYOUNGOPENCLUSTERNGC6383

TheopenclusterNGC6383(α2000=17h34m.8,δ2000=

′

3234)isonly～1.7MyroldandbelongstotheSgrOB1

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