FRAGMENTATION OF ELONGATED CYLINDRICAL CLOUDS .5. DEPENDENCE OF MASS RATIOS ON INITIAL CONDITIONS

Calculations of the formation of nonequal mass binary and multiple systems are presented. The systems are the result of the collapse and fragmentation of rotating elongated clouds which is followed using a three-dimensional smooth particle hydrodynamics (SPH) code. The rotation is parameterized by components parallel and perpendicular to the cloud's major axis. The effects of the rotation, the initial Jeans number J0 (ratio of the absolute value of gravitational to thermal energies), and the cloud's initial density profile are investigated. Binary formation results from the elongated shape of the initial cloud, one fragment forming on each side of the equatorial plane. Slight linear density gradients along the cloud's major axis are sufficient to form nonequal mass fragments. Resultant mass ratios range from 0.1 to 1.0, in agreement with observations. The spatial resolution can affect the mass ratio, especially for low J0 where the fragments form closer together and tidal forces are important. In the presence of rotation, the fragments form with surrounding disks. The accretion rate of the cloud onto the disks and of the disks onto the fragments is found to be greatly affected by tidal interactions at the fragments' closest approach. Accretion onto both the primary and the secondary is enhanced at closest approach due to the tidal forces. The tidal forces depend on the system's mass ratio such that in an unequal mass system the secondary's disk can be completely decimated through accretion. Due to its orbital motion around the primary, the secondary can directly accrete the matter that has gathered in the primary's disk. The secondary is thus less likely to have an appreciable disk, accounting for a redder primary. The binary system's initially high eccentricity decreases with the continued accretion of higher specific angular momentum at apastron and lower specific angular momentum matter at periastron. Multiple systems with unequal mass components are also formed. The systems are composed of an inner binary and a more distant companion. The mass ratio of the companion-binary system is usually less than that of the binary.