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

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.

A method for estimating masses of W Ursae Majoris-type binaries

Masses of W Ursae Majoris-type(W UMa) binaries play a critical role in investigating stellar dynamical evolutionary status. In this paper, we combine the PARSEC(PAdova and TRieste Stellar Evolution Code) with the Roche geometric model to provide a method to determine the masses of W UMa systems. To verify the validity of this method, we compile a sample of 140 spectrum binaries from the literature, which includes 76 W-and 64 A-subtype systems with reliable physical parameters. We find that the average fractional difference and the standard deviation(σM) of the residuals for W-subtype and Asubtype approximately amount to 15.66% and 0.1218, 16.03% and 0.2094, respectively. Meanwhile, we also perform detailed analyses in accordance with the orbital period, the effective temperatures and the mass ratio. We find that the method is more applicable to determine masses for W UMa systems with low effective temperature and short period.

Photometric analysis of V30 of open cluster NGC 7789

We present the photometric solutions of the variable star V30＊ that is in the foreground of intermediate open cluster NGC 7789. The observations were done in the V passband using the 2 m telescope at the IUCAA-Girawali Observatory in India. The analysis is done using the Wilson-Devinney Code （2003） and the fitted light curve is presented. The photometric solutions reveal a W-subtype contact configuration. The photometric mass ratio is found to be 0.395 and the absolute masses and radii for the components are deduced as 1.25Ms and 0.97Rs for the primary and 0.49Ms and 0.93Rs for the secondary, respectively. No signature of third light is found in the system.