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 subsequent encounters. The effect of all encounters, particularly penetrating ones, is to steepen the density profile, increasing the surface density at small radii whilst extensively stripping the disc beyond periastron. In all geometries studied, we find that for penetrating encounters, the surface density profiles outside periastron are well fitted by exponentials. These agree well with recent observations of truncated discs in the Orion Nebula, although we make no attempt to fit specific models or encounter geometries. Repeated passages at the same periastron separation have little effect on the remaining disc mass and the evolution of the orbit of the perturber - it is the first encounter that dominates in both mass redistribution and energy transfer.