The tidal disruption of protoplanetary accretion discs

In this paper we revisit the problem of the tidal interaction occuringbetween a protostellar accretion disc and a secondary point mass following aparabolic trajectory. We model the disc response analytically and we compareour results with three-dimensional SPH simulations. Inviscid as well as viscoushydrodynamics is considered. We show that in a viscous system the responsederived from inviscid considerations is predominant even for the highestestimates of an anomalous disc shear viscosity. The angular momentum lost fromthe disc during the encounter is derived from linear theory, for distantfly-bys, as well as the changes to the disc orientation expected innon-coplanar encounters. It is shown that the target discs can become warpedand precess by a small amount during non-coplanar encounters. This smallprecession is shown to give rise to a relative tilt of the disc which is alwaysmore important for determining its final orientation than is the change to theorbital inclination. We discuss the implications of our results forprotostellar accretion discs and planetary systems.