Final stages of N-body star cluster encounters

We performed numerical simulations of star cluster encounters with Hernquis t's treecode on a CRAY YMP-2E computer. We used different initial condition s (relative positions and velocities, cluster sizes, masses and concentrati on degrees) with the total number of particles per simulation ranging from 4608 to 20 480. Long-term interaction stages (up to 1 Gyr) when the pair co alesces into a single cluster are compared with isolated LMC clusters. Evid ence is found that, when seen in a favourable plane, these resulting cluste rs show elliptical shapes as a result of the disruption of one of the compa nions. These elliptical shapes are essentially time-independent, but they d o depend on the initial structural parameters of the pair components. We al so analysed the fraction of stars that are ejected to the field by the inte raction. We found that this fraction can be almost 50 per cent for the disr upted cluster. These simulations can represent a possible mechanism with wh ich to explain the ellipticity observed in several star clusters in the Mag ellanic Clouds.