Mass-Loss Timescale of Star Clusters in an External Tidal Field. I. Clusters on Circular Orbits

We investigated the evolution of star clusters in a steady external tidal field by means of N-body simulations. We followed seven sets of cluster models, whose central concentration and strength of the tidal field are different. We found that the mass-loss timescale due to the escape of stars, t_mloss, and its dependence on the two-body relaxation timescale, t_{rh, i}, are determined by the strength of the tidal field. The logarithmic slope [≡ d ln(t _mloss)/d ln(t_{rh, i})] approaches unity for the cluster models in weaker tidal fields. The timescale and the dependence are almost independent of the central concentration for clusters in tidal fields of the same strength. In our results, the scaling found by Baumgardt (2001, MNRAS, 325, 1323) can be seen only in cluster models with moderately strong tidal fields.