Proper motions and kinematics of selected bulge globular clusters

Abstract

We computed proper motions of a selected sample of globular clusters projected on the central bulge, employing CCD images gathered along the last 25 yr at the ESO-New Technology Telescope, ESO-Danish and Hubble Space Telescope telescopes. We presented a method to derive their proper motions, and a set of coordinate transformations to obtain 3D Galactic velocity vectors of the clusters. We analysed 10 globular clusters, namely Terzan 1, Terzan 2, Terzan 4, Terzan 9, NGC 6522, NGC 6558, NGC 6540, AL 3, ESO456−SC38 and Palomar 6. For comparison purposes, we also studied the outer bulge cluster NGC 6652. We discuss the general properties of the proper-motion-cleaned colour–magnitude Diagrams, derived for the first time for most of them. A general conclusion is that the inner bulge globular clusters have clearly lower transverse motions (and spatial velocities) than halo clusters, and appear to be trapped in the bulge bar.