1997NewA....2..477O

We present and analyse space motions and orbits for a sample of 15 galactic globular clusters. The absolute proper motions of these clusters have been determined with respect to reference stars of the new Hipparcos system. Orbital integrations in two model potentials for the Galaxy are considered. The sample shows a mean rotation near 40 km s^ - 1 in the sense of rotation of the galactic disk. Six clusters are however found to be in retrograde motion. Velocity dispersions are around 104 km s^ - 1 in the direction of rotation, near 116 km s^ - 1 in latitudinal direction and near 127 km s^ - 1 in radial direction. The orbits of the clusters preferentially have small axial angular momenta and high eccentricities, the median of the orbital eccentricities being 0.62. From the spatial extent of the orbits we conclude that the Galaxy must have a massive halo with a radius of at least 30 kpc. The space density distribution of our sample of clusters as derived from averaging over their orbits resembles the observed space density distribution of the total globular cluster system, except for distances less than 4 kpc from the galactic center. The largest apogalactic distances in the sample reach out to 65 kpc. The orbits provide evidence that the more metal-rich clusters are concentrated towards the galactic center. The clusters with significant retrograde motion have metal abundances between - 1.5 and - 2.0 and hence appear to be relatively homogeneous in chemical composition. The small subgroup of `young halo' clusters within our sample is orbiting with a net retrograde rotation of - 9 km s^ - 1. A general relation between orbital eccentricity and metal-abundance does not show up in the sample. The observed radii of the clusters are found to be in a well-defined relation to the tidal limits imposed by orbital motion in the galactic field. It is shown that the cluster radii are however not uniquely determined by the perigalactic distances, but involve at least also the geometry of the orbit.