Star cluster evolution with primordial binaries. II - Detailed analysis

The evolution of globular cluster models containing significant numbers of primordial binaries is followed to the point at which the primordial fuel is spent and the behavior reverts to the 'single-star' form. This point is reached after some 30 initial core collapse times when the cluster has expanded by a factor of about five to seven. For N about 1100, the ratio of core radius to virial radius just after core collapse is about 0.12. This ratio then drops linearly in comoving time, reaching the asymptotic single-star value of about 0.05. The core mass drops by a factor of two during this time. The first detailed statistical study of the spatial evolution of the binary population in a star cluster is also reported. The mass fraction of binaries in the core shows a steady, near-linear decrease from 0.5 to 0.1 between 20 and 250 instantaneous half-mass crossing times. Hard binaries are found to harden both through the effects of strong scattering and through the declining energy scale set by the expanding cluster. 23 refs