The structure of star clusters. III. Some simple dynamical models

Dynamical models of star clusters are presented, based on steady-state solutions of the Fokker-Planck equation. The models are spatially limited, corresponding to the tidal cutoff imposed by the Milky Way. Their projected density distributions are similar to those observed in open clusters, globular clusters, and elliptical galaxies. Within each model the fractional escape rate is uniform throughout. The escape rate from a cluster depends on the number of stars and the strength of the tidal force field; when expressed in this way it is almost independent of core radius or central concentration. Quantitative application to actual clusters must await a discussion of models containing a realistic stellar mixture.