FRAGMENTATION OF ELONGATED CYLINDRICAL CLOUDS .6. COMPARISON WITH OBSERVATIONS

A comparison of hydrodynamical simulations of the collapse and fragmentation of elongated clouds with observations of molecular cores, star formation regions, and binary and multiple systems is presented. Observations of molecular cloud cores suggest appropriate initial conditions for numerical simulations of star formation. They include an elongated structure with rotation about an arbitrary axis and low values of beta, the ratio of the absolute value of rotational to gravitational energies. The environments of young stellar objects display ''warped'' disks, and ''bridges'' of matter between young binaries, both of which are formed in our simulations. The kinematics of star-forming regions are explored, and a model is proposed where large line widths are explained by the dynamical process of infall and star formation. Simulations of the formation and continued accretion of non-equal-mass binary systems are compared with observed differential reddening and IR companions in pre-main-sequence (PMS) binaries. The presence of an infrared companion could also explain the flat spectral energy distribution of some PMS stars. The properties of main-sequence binaries are discussed with a view to the numerical models. The formation of binary systems from the fragmentation of elongated clouds casily explains the large eccentricities observed and the period-eccentricity relation. A spread in eccentricities arises through dissipative disk-disk interactions at closest approach. All separations greater than 50 AU can be explained by the numerical simulations, while separations less than 50 AU are possible (but have not yet been attained) with lower initial beta or greater disk-disk interactions. The formation of multiple systems is also discussed, and the observation of noncoplanarity in at least 35% of the multiple systems is explained in terms of the fragmentation of an elongated cloud with rotation about an arbitrary axis. The difference in mass ratios between the inner and outer systems can also be explained in terms of the different fragmentation processes involved.