MASS SEGREGATION IN THE GLOBULAR-CLUSTER NGC-6397

Our deep HST images of the center of the globular cluster NGC 6397 are almost devoid of faint stars, implying that these stars must be much less concentrated to the cluster center than the brighter stars. This difference is an expected consequence of energy exchanges through stel lar encounters, which give higher velocities to lower mass stars and c ause them to have a larger average distance from the cluster center. T he amount of segregation that we observe is consistent with the predic tions of a multimass model in dynamical equilibrium.