Photometric Study of Variable Stars in the Open Cluster NGC

We report the discovery of 19 variable stars and two blue–stragglers in the field of the open cluster NGC 6866. Three of the variable stars we classify as δ Sct, two, as γ Dor, four, as W UMa, two, as ellipsoidal variables, and one, as an eclipsing binary. Seven stars show irregular variability. Two of the pulsators, a δ Sct star NGC 6866-29 and a γ Dor star NGC 6866-21, are multiperiodic. From an analysis of proper motions, we conclude that the δ Sct stars, one of the γ Dor stars and both blue–stragglers are very probable members of the cluster. The position on the color-magnitude diagram of seven other variables suggests that they also belong to the cluster. The eclipsing binary, which we discover to be a new high-velocity star, and the seven irregular variables are non-members. Then, we discuss in detail the age and metallicity of open clusters that host γ Dor stars and we show that none of these parameters is correlated with the number of γ Dor stars in cluster.