Photometric studies of intermediate and old age galactic star clusters

Abstract

We present a detailed analysis of five intermediate / old age open star clusters, based on the CCD UBVRI data. We have used a new colour index parameter (CIP), which is the difference in colour index between the blue turn off point (BTO) of the main sequence and the colour at the base of the red giant branch (BRGB), to estimate morphological age of the cluster. This parameter is useful for the clusters which have no noticeable red giant clump. We find that morphological features of the colour magnitude diagram (CMD) are better understood in terms of convective core overshooting. Age of the clusters under study ranges between 0.6-5 Gyr. We have studied the mass function and structure of all the clusters. Mass function slopes for three clusters are in agreement with the Salpeter (1955) value. Spatial variation of mass function along the clusters is also studied. Mass segregation is observed in three clusters. Since all these clusters are dynamically relaxed, the observed mass segregation is therefore most likely due to the dynamical evolution processes.