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N-Body Simulations of Star-Disc Captures in Globular Clusters

The presence of protostellar disks can greatly increase the dissipation during close stellar encounters, leading to the formation of a significant population of binaries during the initial collapse and virialization of a cluster. We have used N-body simulations of collapsing globular clusters to find the major factors that determine the efficiency of binary formation through star-disk captures. This work serves the dual purpose of verifying the results of earlier analytic work as well as examining parameters not testable by that work. As in the earlier work, typical binary fractions of a few percent are found. For the parameters studied, the results are found to depend remarkably little upon disk evolution, the mass distribution of the stars, or their spatial distribution, though distributions in which the stars are highly clumped yield binary fractions larger by a factor of a few. The direct N-body integrations limit the models to relatively small values of N. Semiempirical relations are derived, however, which allow the results to be extrapolated to values of N appropriate to globular clusters.