Mass Loss Timescale of Star Clusters in External Tidal Field

Abstract

We investigate evolution of star clusters in 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 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 [$= dln(t_{mloss})/dln(t_{rh,i})$] approaches to near unity for the cluster models in weaker tidal field. The timescale and the dependence are almost independent of the central concentration for clusters in the tidal field of the same strength. In our results, the scaling found by Baumgardt (2001) can be seen only in the cluster models with moderately strong tidal field.