Accretion during binary star formation -- I. Ballistic accretion

We consider the effects of accretion, during binary star formation, on the mass ratio and separation of a 'seed' binary system. Numerical fragmentation calculations show that 'seed' binary systems may be formed during the gravitational collapse of molecular cloud cores. When initially formed, however, these protobinaries typically contain only a small fraction of the total mass of the cloud core. For the star formation process to reach completion, a protobinary system must grow in mass via accretion from the remainder of the infalling cloud. The accretion of, and interaction with, this matter affects the mass ratio, separation and eccentricity of the protobinary, and thus the final state of the system cannot be determined unless the effects of the accretion are known.