A search for variable stars in the four open star clusters

Abstract

We present a CCD photometric survey for the search of variable stars in four open clusters namely Berkeley 69, King 5, King 7 and Berkeley 20. The time series observations were carried out for 1 and/or 2 nights for each of the clusters in the year 1998, which have led to identify nineteen variable stars in these clusters. Out of these 19 variable stars, five stars show $\delta$ Scuti-like variability and two stars show W UMa type variability. In other stars, we could not find the periods, and hence the type of variability due to the lack of sufficient data. The periods of $\delta$ Scuti type stars are found to be in the range of 0.13–0.21 days, whereas the two stars in the cluster Berkeley 20, which showed W UMa type variability have orbital periods of 0.396 and 0.418 days, respectively. Using the Gaia data, the basic parameters of the clusters Berkeley 69, King 7 and King 5 are also revised. The age and reddening are estimated to be $0.79\pm 0.09$ Gyr and $0.68\pm 0.03$ mag for Berkeley 69, $0.79\pm 0.09$ Gyr and $1.22\pm 0.03$ mag for the cluster King 7 and $1.59\pm 0.19$ Gyr and $0.63\pm 0.02$ mag for the cluster King 5, respectively. The signature of mass segregation is found in the clusters King 7 and King 5.