Space Velocities of Southern Globular Clusters. IV. First Results for Inner Galaxy Clusters

Abstract

We have measured the absolute proper motions of four low-latitude, inner Galaxy globular clusters. These clusters are NGC 6266 (M62), NGC 6304, NGC 6316, and NGC 6723. The proper motions are on the Hipparcos system, since no background extragalactic objects are found in these high-extinction regions. The proper-motion uncertainties range between 0.3 and 0.6 mas yr-1. We discuss the kinematics of these clusters and of three additional bulge clusters-NGC 6522, NGC 6528, and NGC 6553-whose proper motions with respect to bulge stars had been determined previously. We find that all of the clusters have velocities that confine them to the bulge region. Of the three metal-poor clusters ([Fe/H] =-1.0), NGC 6304 and NGC 6553 also have kinematics consistent with membership to a rotationally supported system. NGC 6528 has kinematics, metallicity, and mass that argue in favor of a genuine Milky Way bar cluster. NGC 6316's kinematics indicate membership to a hotter system than the bar.