Stellar contents of the open clusters Be 64 and Be 69

Abstract

We present UBVRI CCD photometry for previously unstudied open clusters (Be 64 and Be 69). Photometry has also been carried out for nearby elds to correct for the eects of eld stars contamination. From the colour-colour diagram the reddening for Be 64 and Be 69 is estimated to be 1.05 mag and 0.65 mag respectively. In case of Be 69 the comparison of obser- vational colour - magnitude diagram (CMD) with the standard isochrones of VandenBerg (1985) indicates an apparent discrepancy between the shape of the turno and isochrones. The morphological features of the CMDs of Be 69 are better understood in terms of convective overshooting. The comparison of CMDs of both the clus- ters with the convective overshoot models (Bertelli et al. 1994) produces a good t for a metallicity Z =0 :008 and age = 0:8 1:0 Gyr. An apparent distance modulus (m M )=1 6 :2 and 14.3 has been estimated for Be 64 and Be 69, respectively, which corresponds to a distance of 3880 480 pc and 2860 310 pc, respectively. Star clusters constitute a principal link between the theo- ries of stellar evolution and the observable universe. Open clusters are important tools to analyze the properties of the galactic disk and to test the theories of galactic and stellar evolution. The comparison between the HR dia- gram of the observed clusters and the isochrones, com- puted by means of evolutionary models, provides a test of stellar structure and evolution. The comparison pro- vides an opportunity to ascertain whether or not convec- tive overshoot plays an important role in the evolution. Only about one third of the open clusters of the Milky Way have well studied HR diagrams to estimate