Monte Carlo Simulations of Globular Cluster Evolution. IV. Direct Integration of Strong Interactions

We study the dynamical evolution of globular clusters containing populationsof primordial binaries, using our newly updated Monte Carlo cluster evolutioncode with the inclusion of direct integration of binary scatteringinteractions. We describe the modifications we have made to the code, as wellas improvements we have made to the core Monte Carlo method. We present severaltest calculations to verify the validity of the new code, and perform manycomparisons with previous analytical and numerical work in the literature. Wesimulate the evolution of a large grid of models, with a wide range of initialcluster profiles, and with binary fractions ranging from 0 to 1, and comparewith observations of Galactic globular clusters. We find that our code yieldsvery good agreement with direct N-body simulations of clusters with primordialbinaries, but yields some results that differ significantly from otherapproximate methods. Notably, the direct integration of binary interactionsreduces their energy generation rate relative to the simple recipes used inPaper III, and yields smaller core radii. Our results for the structuralparameters of clusters during the binary-burning phase are now in the tail ofthe range of parameters for observed clusters, implying that either clustersare born significantly more or less centrally concentrated than has beenpreviously considered, or that there are additional physical processes beyondtwo-body relaxation and binary interactions that affect the structuralcharacteristics of clusters.Comment: Accepted for publication in ApJ; 17 pages, 19 figures; changes to reflect accepted versio