CIRCUMSTELLAR DISC DENSITY PROFILES - A DYNAMIC APPROACH

We have evaluated the effect on both disc mass and density profile of a system undergoing close and penetrating encounters with a perturber star. From our post-encounter particle distributions we have generated post-encounter surface density profiles and allowed them to suffer su bsequent encounters. The effect of all encounters, particularly penetr ating ones, is to steepen the density profile, increasing the surface density at small radii whilst extensively stripping the disc beyond pe riastron. In all geometries studied, we find that for penetrating enco unters, the surface density profiles outside periastron are well fitte d by exponentials. These agree well with recent observations of trunca ted discs in the Orion Nebula, although we make no attempt to fit spec ific models or encounter geometries. Repeated passages at the same per iastron separation have little effect on the remaining disc mass and t he evolution of the orbit of the perturber - it is the first encounter that dominates in both mass redistribution and energy transfer.