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

We investigate evolution of star clusters in external tidal field by means of$N$-body simulations. We followed seven sets of cluster models whose centralconcentration and strength of the tidal field are different. We found that themass loss timescale due to escape of stars, $t_{mloss}$, and its dependence onthe two-body relaxation timescale, $t_{rh,i}$, are determined by the strengthof the tidal field. The logarithmic slope [$= dln(t_{mloss})/dln(t_{rh,i})$]approaches to near unity for the cluster models in weaker tidal field. Thetimescale and the dependence are almost independent of the centralconcentration for clusters in the tidal field of the same strength. In ourresults, the scaling found by Baumgardt (2001) can be seen only in the clustermodels with moderately strong tidal field.Comment: 19 pages, 15 figures, submitted to PAS