ENCOUNTERS WITH PROTOSTELLAR DISKS .2. DISRUPTION AND BINARY FORMATION

The disruption of a circumstellar disk during a stellar encounter and the accompanying dissipation of orbital energy are numerically simulated. It is found that an average impacting encounter produces a mass loss of less than about half of the initial disk mass. Even in dense stellar environments encounters are unlikely to play a prominent role in dispersing disks, though densities in the outer parts can be significantly reduced. A large fraction of the disk material may be captured by the perturber or ejected from the system. No material is found to form a circumbinary disk. Though the planar retrograde encounters are found to be particularly efficient at dissipating orbital energy, estimated rates indicate that capture is not a dominant process for the formation of binaries in stellar clusters. However, the rates may be greatly underestimated if substructure exists or interactions occur during the star-formation process.