Photometric study of W UMa type binaries in the old open cluster Berkeley 39

The study of W UMa binary systems gives a wealth of information about their nature as well as their parent bodies （if any）, like clusters. In this paper, we present the I passband photometric solutions of four W UMa binaries in the open cluster Berkeley 39 using the latest version of the W-D program. The result shows that two binary systems are W-subtype W UMa binary systems and the other two systems are H-subtype W UMa binary systems. No third body has been found in any of the four systems. We found a correlation between the period and mass-ratio as well as temperature and mass-ratio for the respective variables, which is similar to the relationship between mass ratio and total mass of the contact binaries as shown by van＇t Veer and Li et al.