FORMATION AND COLLAPSE OF NONAXISYMMETRIC PROTOSTELLAR CORES IN PLANAR MAGNETIC MOLECULAR CLOUDS

摘要

We extend our earlier work on ambipolar diffusion-induced formation of protostellar cores in isothermal sheetlike magnetic interstellar clouds by studying nonaxisymmetric collapse for the physically interesting regime of magnetically critical and supercritical model clouds (μ_0 ≥ 1, where μ_0 is the initial mass-to-magnetic flux ratio in units of the critical value for gravitational collapse). Cores that form in model simulations are effectively triaxial, with shapes that are typically closer to being oblate rather than prolate. Infall velocities in the critical model (μ_0 = 1) are subsonic; in contrast, a supercritical model (μ_0 = 2) has extended supersonic infall that may be excluded by observations. For the magnetically critical model, ambipolar diffusion forms cores that are supercritical (μ_(core) > 1) and embedded within subcritical envelopes (μ_(env) < 1). Cores in our models have density profiles that eventually merge into a near-uniform background, which is suggestive of observed properties of cloud cores.