A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. VIII. NGC 6834

摘要

We present results of a CCD variability search in the field of the young open cluster NGC 6834. We discover 15 stars to be variable in light. The brightest, a multiperiodic γ Doradus-type variable is a foreground star. The eight fainter ones, including a γ Cassiopeiae-type variable, two λ Eridani-type variables, an ellipsoidal variable, an EB-type eclipsing binary, and three variable stars we could not classify, all have E(B-V) within proper range, thus fulfilling the necessary condition to be members. One of the three unclassified variables may be a non-member on account of its large angular distance from the center of the cluster. Four of the six faintest variable stars, which include two eclipsing binaries and two very red stars showing year-to-year variations, are certain non-members. One of the remaining two faintest variable stars, an EA-type eclipsing binary may be a member, while the faintest one, a W Ursae Majoris-type variable, is probably a non-member. For 6937 stars we provide the V magnitudes and V-I_C color indices on the standard system. Because of nonuniform reddening over the cluster's face, a direct comparison of these data with theoretical isochrones is not possible. We therefore obtain E(B-V) from available UBV photometry, determine the lower and upper bound of E(B-V) for NGC 6834, and then fit properly reddened Padova isochrones to the data. Assuming HDE 332843, an early-F supergiant, to be a member we obtain log(age/yr) = 7.70, V_O-M_V = 12.10 mag. For 103 brightest stars in our field we obtained the a index, a measure of the equivalent widths of the Ha line. We find Hα emission in five stars, including the γ Cas-type variable and the two λ Eri-type variables.