Comparing Direct N-Body Integration with Anisotropic Gaseous Models of Star Clusters

Abstract

We compare the results for the dynamical evolution of star clusters derived from anisotropic gaseous models with the data from N-body simulations of isolated and one-component systems, each having modest number of stars. The statistical quality of N-body data was improved by averaging results from many N-body runs, each with the same initial parameters but with different sequences of random numbers used to initialize positions and velocities of the particles. We study the development of anisotropy, the spatial evolution and energy generation by three-body binaries and its N-dependence. We estimate the following free parameters of anisotropic gaseous models: the time scale for collisional anisotropy decay and the coefficient in the formulae for energy generation by three-body binaries. To achieve a fair agreement between N-body and gaseous models for the core in pre- as well as in post-collapse only the energy generation by binaries had to be varied by N. We find that anisotropy has considerable influence on the spatial structure of the cluster particularly for the intermediate and outer regions.