Proper motions in the field of the globular cluster NGC 6934.

Abstract

We measured relative proper motions with a typical accuracy of 1.0 millarcsec/year (mas/a) for 2000 stars in a 1.4 deg x 1.4 deg field around the low-latitude globular cluster NGC 6934. Four plates taken with the Bonn double refractor, spanning an epoch difference of 62 years, were digitized completely. Within the tidal radius of the cluster, we find 106 stars with proper motion errors less than 5 mas/a. Membership probabilities are computed taking into account the individual proper motion errors and the radial distances to the cluster center. We derive the mean relative proper motion of NGC 6934 using stars with high membership probabilities from radial velocities or from their location in the color-magnitude diagram. The relative proper motions of four Hipparcos stars in the field will be used to obtain the absolute proper motion of NGC 6934 once the extragalactically calibrated Hipparcos Output Catalog is available.