STAR CLUSTER EVOLUTION WITH PRIMORDIAL BINARIES .2. DETAILED ANALYSIS

We have followed the evolution of globular cluster models containing significant numbers of primordial binaries (about 100 binaries in a 1100 star model), up to the point at which the primordial fuel is spent. This occurs on a time scale about 30 times longer than the original core collapse time. Because of the large numbers of both single stars and binaries present during the first few core collapse times, strong interactions with individual binaries do not dominate the behavior of the cluster, in contrast with all previous studies. The absence of the corresponding wild fluctuations permits a detailed analysis of the average behavior of various cluster parameters. The ratio of the core radius to the half-mass radius is about 0.1 immediately after core collapse, and drops to about 0.05 by the time most of the binaries have been destroyed. The core mass similarly drops by a factor of 2 during this time. The mass fraction of binaries in the core shows a steady, nearlinear decrease from 0.5 to 0.1 between tau approximately 20 and tau approximately 250, where the time increment d-tau is measured in units of the instantaneous half-mass crossing time. We present the first detailed statistical study of the spatial and temporal variations in the binary population throughout a star cluster. Our detailed migration statistics reflect the opposing trends of mass segregation and recoil from energetic interactions in the core. Since we use a direct integration method, based on Aarseth's NBODY5 code, we have also obtained a wealth of microscopic information concerning individual interactions between single stars, binaries, triples, and occasionally more complex multiple-star systems. We present a study of binary interactions in the context of a real cluster environment, and compare our results with earlier "laboratory" simulations, in which similar interactions were studied in isolation. In addition we have performed studies of the formation and evolution of hierarchical triple systems, and the generation of energy within short-lived, overdense "clumps" of stars, rather than via binary interactions in an otherwise smooth background. These data will be useful for future quantitative modeling of processes connected with the origin and evolution of X-ray binaries and millisecond pulsars in globular clusters.