Persistence of Plummer-Distributed Small Globular Clusters as a Function of Primordial-Binary Population Size

摘要

Globular stellar clusters are relatively common. All globular clusters that have been observed are relatively large (～10~4 - 10~6 stars). In the absence of other influences, many if not all globular clusters continually lose mass as stars escape their gravitational hold. It has been hypothesized that the presence of primordial binaries helps to increase the persistence of small (～1000-star) globular clusters. Here I use N-body gravitational simulation of isotropic, Plummer-distributed, small globular clusters, with stellar evolution, to assess the persistence of such clusters as a function of initial populations of 100-500 primordial binaries (representing 0.1 - 0.5 of the initial cluster mass). The simulation predicts that in such clusters (a) star-loss is roughly linear in time up to ～300 Myr after t_0, (b) cluster persistence is, more or less, an increasing function of the fraction of primordial binaries at t_0, when such binaries account for 0.1-0.5 of the initial cluster mass.