The Araucaria Project. Variable stars outside the Local Group: NGC 300

Abstract

ABSTRACT Wehave performed a search for variable stars in the Sculptor Group spiral galaxy NGC 300using wide-Þeld multi-epoch BV photometry up to a limiting magnitude V 23. Apart fromthe Cepheid variables in this galaxy already reported in an earlier paper by Pietrzynski« et al.and the variable blue supergiants reported by Bresolin et al., we have identiÞed 26 additionalperiodicvariables,withperiodsrangingfrom0.2to190d,and121slowvariables.Twoofthesenewly discovered variables are Galactic foreground stars (one of them is a W UMa system),and three correspond to previously identiÞed Wolf—Rayet stars. 16 stars are new Cepheids,and the other objects span a huge range in colours and represent a mixture of different typesof luminous variables. Key words: supergiants — Cepheids — stars: Wolf—Rayet — galaxies: stellar content. 1 INTRODUCTION Variablestarsingalaxiestracethehistoryoftheirstellarpopulations,and their study is important to understand the properties and currentevolutionary state of the host galaxy. In particular, the study of themost luminous variables in galaxies spanning a range of metallici-ties could enlighten the processes involved in the rather short, andsometimes spectacular, events observed near the end of the lives ofthe more massive stars.Past work on variable stars in galaxies has been mostly restrictedto the Local Group (Mateo 1998, and references therein). In con-trast, very few projects aimed at exploring the populations of vari-able stars outside the Local Group have been executed. One of thetargets which has received some attention over the last years, how-ever, mostly in the context of a revision of the extragalactic dis-tance scale in the framework of the Araucaria Project (Gieren et al.2001) has been the spiral galaxy NGC 300. NGC 300 is located inthe Sculptor Group at a distance of about 2 Mpc (Freedman et al.2001). Its metallicity is approximately bracketed by the Milky Wayand Small Magellanic Cloud (Urbaneja et al. 2003). Because ofits low inclination, NGC 300 is well suited to studies of its stel-lar content. Recent surveys include Wolf—Rayet stars (Schild et al.2003; Bresolin et al. 2002b), blue supergiants (Urbaneja et al. 2003;Bresolin et al. 2002a), Cepheids (Pietrzynski« et al. 2002), OB asso-ciations (Pietrzynski« et al. 2001) and supernova remnants (Pannutiet al. 2000). In this paper we use the photometric data base providedby Pietrzy«nski et al. (2002) to search for variable stars in NGC 300.In that paper, a search for Cepheid variables had already been con-ductedfromthesamedatasetandmorethanahundredofthemwerefound. This same observational material was very recently used by