CCD photometry of W UMa-type contact binaries in the old open cluster Berkeley 39

Abstract

We present the combined BVI multicolor photometric solutions of seven EW variables in the old open cluster Berkeley 39. The observations were carried out in the B and V passbands from the 2 m telescope at the IUCAA-Girawali Observatory in India. The analysis is done using the 2003 version of the Wilson-Devinney code and the fitted light curves are presented. The light curves appear to be symmetric in all the passbands. The photometric solutions suggest that the variables are W-type systems. The new ephemeris indicates that the orbital periods of the studied variables have not changed during the timespan of observations. Revised orbital period, absolute mass, radius and luminosity of the respective variables are presented. The absolute physical parameters of the variables follow the trend of field EW stars. Comparing the results obtained with the other theoretical works, we suggest that there is an excess loss of mass and angular momentum in these systems which may be due to their short period and relatively young age, possibly due to the presence of a third component or the initial detached period being less than 2 d.