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R. F. Rees (Westfield State College and Yerkes Observatory), K. M. Cudworth (Yerkes Observatory, The University of Chicago)
NGC 6397 is a nearby (~2.2 kpc) core-collapsed globular cluster, currently about 0.5 kpc from the Galactic plane. Proper motions of several hundred stars in the field of NGC 6397 derived from thirty plates spanning 97 years show that the cluster is moving away from the disk. At its current Z velocity, the cluster would have passed through the disk 4.7 Myr ago, an upper limit as the gravitational attraction of the disk must have slowed it. A calculation with a simple Galactic disk potential gives a more realistic disk passage about 3 Myr ago. This is more than two orders of magnitude less than the median relaxation time of 850 Myr (Djorgovski 1993, ASPCS 50, 373). A search for tidal tails (Leon et al. 2000, A&A, 359, 907) was inconclusive due to the moderately high and patchy absorption in the direction of NGC 6397. Although our data do not extend to the tidal radius, the proper motions of the cluster members will be examined for evidence of the disk passage. This research has been partially supported by the NSF.