Capture‐formed Binaries via Encounters with Massive Protostars

Most massive stars are found in the center of dense clusters, and have acompanion fraction much higher than their lower mass siblings; the massivestars of the Trapezium core in Orion have ~ 1.5 companions each. This highmultiplicity could be a consequence of formation via a capture scenario, or itcould be due to fragmentation of the cores that form the massive stars. Duringstellar formation circumstellar disks appear to be nearly ubiquitous. Theirlarge radii compared to stellar sizes increase the interaction radiussignificantly, suggesting that disk interactions with neighboring stars couldassist in capturing binary companions. This mechanism has been studied forstars of approximately solar mass and found to be inefficient. In this paper wepresent simulations of interactions between a 22 Msun star-disk system and lessmassive impactors, to study the disk-assisted capture formation of binaries ina regime suited to massive stars. The formation of binaries by capture is foundto be much more efficient for massive capturers. We discuss the effects of amass dependent velocity dispersion and mass segregation on the capture rates,and consider the long term survival of the resultant binaries in a densecluster.Comment: 16 pages, 10 figures, accepted to Ap