Fokker-Planck calculations of star clusters with primordial binaries

We have modified the multimass Fokker-Planck code developed by Murphy & Cohn to allow for a distribution of internal binary binding energies, as well as the usual distribution of orbital energies in the cluster potential. Interactions between binaries and single stars and between pairs of binaries are simulated; these exchange energy between internal and external degrees of freedom and strongly influence the evolution both of the binary population and of the cluster as a whole. Calculations have been made for initial populations of 5%, 10%, and 20% hard binaries by number. Mass stratification and modest core contraction proceed during the first ∼ 10t_rh(0) (initial half-mass relaxation times), followed by a period of ∼ few × 10t_rh(0) during which the core radius is nearly constant, and then by gravothermal oscillations. The binaries are typically able to power expansion of the cluster for ∼ 100t_rh(0), or ∼ 10 times the final t_rh; at the end of this period, the initial binary population has been reduced by more than half through disruptions and ejections. Ejections are a more important energy source than direct heating. Implications for globular clusters are discussed.