Encounters between binary and single stars and their effect on the dynamical evolution of stellar systems

Results are reported for an investigation of the effect of preexisting binaries on the evolution of stellar clusters. The investigation was conducted by running more than 14,000 computer-simulated encounters between binaries and field stars for various preencounter relative velocities (Vf) and impact parameters. It is shown that at low values of Vf, an encounter causes a binary orbit to shrink and become more tightly bound. In this case, the two more massive of the three stars involved in the encounter will remain in the binary system while the third will be ejected from it at a relatively high velocity. It is found that the shrinking of more tightly bound binary orbits will destroy an open cluster in a few hundred million years unless the cluster is unusually massive or unusually deficient in binary stars. It is also found that binary stars are likely to limit the maximum density attainable in the nucleus of a globular cluster.