Capture‐formed Binaries via Encounters with Massive Protostars

Abstract

Most massive stars are found in the center of dense clusters and have acompanion fraction much higher than their lower mass siblings; themassive stars of the Trapezium core in Orion have ~1.5 companions each.This high multiplicity could be a consequence of formation via a capturescenario, or it could be due to fragmentation of the cores that form themassive stars. During stellar formation circumstellar disks appear to benearly ubiquitous. Their large radii compared to stellar sizes increasethe interaction radius significantly, suggesting that disk interactionswith neighboring stars could assist in capturing binary companions. Thismechanism has been studied for stars of approximately solar mass andfound to be inefficient. In this paper we present simulations ofinteractions between a 22 M_{solar} star-disk system and lessmassive impactors in order to study the disk-assisted capture formationof binaries in a regime suited to massive stars. The formation ofbinaries by capture is found to be much more efficient for massivecapturers. We discuss the effects of a mass-dependent velocitydispersion and mass segregation on the capture rates and consider thelong-term survival of the resulting binaries in a dense cluster.