Statistics of N-body simulations -- IV. Unequal masses with a tidal field

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Abstract
We report results of a large number of collisional N-body simulations including a mass spectrum and a tidal field. We emphasize the ways in which evolution differs from that observed in isolated systems, by comparison with earlier papers in this series. We show that the evolution hardly alters if the tidal field is replaced by a tidal cut-off. Core collapse is almost unaffected by the tide, but the subsequent post-collapse expansion is eventually reversed by the time that tidal limitation becomes important. As in isolated models, mass segregation almost stops by the end of core collapse; after core bounce there is a substantial increase in the mean mass, caused by preferential escape of stars of low mass. The early phase of rapid mass segregation is also characterized by an approach to equipartition in the inner parts of the system, although the outer parts remain far from equipartition. Even here, however, there is a slow tendency to equipartition in post-collapse expansion, as the tidal stripping of the outer parts gradually exposes parts of the cluster where equipartition was partially established. Similar remarks apply to the evolution of the anisotropy. The evolution of the core is virtually unaffected by the tide until well after core bounce; in late post-collapse evolution there is a tendency for the mass of the core to decrease slightly, whereas it is nearly constant in isolated models. Similarly, in the presence of a tide the mean number of binaries in the system tends to decrease after the end of core collapse. The total internal binding energy in bound binaries is smaller than at comparable stages of post-collapse evolution in isolated systems. In the overall energy budget, one obvious difference between isolated and tidally limited models is that the energy of escaping single stars is initially negative, although it becomes positive later as the energy carried off by ejecta from three-body interactions becomes dominant.

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