THE KINEMATICS OF GLOBULAR-CLUSTERS, APOCENTRIC DISTANCES AND A HALO METALLICITY GRADIENT

We have studied a sample of 26 globular clusters for which so far abso lute proper motions were published in the literature. From the proper motions, distances, and radial velocities we derived space motions of the globular clusters and via numerical integration also the orbits of the clusters in the Galaxy. Orbital eccentricities, total energy, the apo- and perigalactic distances and the maximum distance from the gal actic plane and their relation to the metallicity of the clusters have been studied. We find that 10 of the globular clusters are on retrogr ade orbits. Globular clusters with metallicity larger than [Fe/H]=-1.4 appear to have smaller orbits than the metal poorer clusters. Our dat a indicate for the first time an abundance gradient in the halo globul ar clusters.