Variable stars in the open cluster NGC 6811

Abstract

We performed a time-series B, V band CCD photometric observations of the open cluster NGC 6811 to search for variable stars. A total number of 16 variables were detected including nine new ones. They are classified as 12 δ Scuti stars and four unknown type variables. The 12 δ Scuti variables are all very likely members of the cluster. This makes NGC 6811 a very important target for asteroseismology of dwarf Cepheids. In addition, we have carried out an isochrone fitting on the V vs. B– V CMD of the cluster based on theoretical models. It gives an age of log ( t ) = 8.76 ± 0.09 for the cluster with the solar metallicity ( Z = 0.019). The distance modulus and color excess of NGC 6811 are determined to be ( m - M ) V = 10.59 ± 0.09 and E ( B - V ) = 0.12 ± 0.05 , respectively. A preliminary Fourier analysis shows a few very interesting sequences of period-luminosity relations, with the fundamental mode matches the P– L relation defined by previous studies for δ Scuti variables with high precision observations. This also confirms that all the 12 δ Scuti stars observed in this work are highly probable members of NGC 6811.