The Decay of Accreting Triple Systems as Brown Dwarf Formation Scenario

We investigate the dynamical decay of non-hierarchical accreting triplesystems and its implications on the ejection model as Brown Dwarf formationscenario. A modified chain-regularization scheme is used to integrate theequations of motion, that also allows for mass changes over time as well as formomentum transfer from the accreted gas mass onto the bodies. We integrate anensemble of triple systems within a certain volume with different accretionrates, assuming several prescriptions of how momentum is transferred onto thebodies. We follow their evolution until the systems have decayed. We analyzethe end states and decay times of these systems and determine the fraction ofBrown Dwarfs formed, their escape speeds as well as the semi-major axisdistribution of the formed Brown Dwarf binaries. We find that the formationprobability of Brown Dwarfs depends strongly on the assumed momentum transferwhich is related to the motion of the gas. Due to ongoing accretion andconsequent shrinkage of the systems, the median escape velocity is increased bya factor of 2 and the binary separations are decreased by a factor of 5compared with non-accreting systems. Furthermore, the obtained semi-major axisdistribution drops off sharply to either side of the median, which is alsosupported by observations. We conclude that accretion and momentum transfer ofaccreted gas during the dynamical decay of triple systems is able to producethe observed distribution of close binary Brown Dwarfs, making the ejectionmodel a viable option as Brown Dwarf formation scenario.Comment: 31 pages, 8 figures, accepted for publication in Ap