Orbital decay of protostellar binaries in molecular clouds

Abstract

The evolution of protostellar binary system is investigated while it is embedded in its parent molecular cloud core and is acted upon by gas drag as a result of dynamical friction. Approximate analytical results are obtained for the energy and angular momentum evolution of the orbit in limiting cases, where the velocity is much smaller than, and much larger than, the velocity dispersion of the gas. The general case is solved numerically. Dispersion causes a decay of the orbit to smaller separations and orbital eccentricity increases with time. Binary populations have been statistically generated and evolved for comparison with observation of the frequency distributions with periods of main-sequence (PMS) binaries. Decay of the orbit as a result of dynamical friction can circumvent the problem of forming close binaries, as long period binaries get dragged and evolve to shorter periods.