Protostellar collapse induced by compression. II: rotation and fragmentation

Abstract

We investigate numerically and semi-analytically the collapse of low-mass, rotating prestellar cores. Initially, the cores are in approximate equilibrium with low rotation (the initial ratio of thermal to gravitational energy is $α_0 \simeq 0.5$, and the initial ratio of rotational to gravitational energy is $β_0 = 0.02 {\rm to} 0.05$). They are then subjected to a steady increase in external pressure. Fragmentation is promoted -- in the sense that more protostars are formed -- both by more rapid compression, and by higher rotation (larger $β_0$). In general, the large-scale collapse is non-homologous, and follows the pattern described in Paper I for non-rotating clouds, viz. a compression wave is driven into the cloud, thereby increasing the density and the inflow velocity. The effects of rotation become important at the centre, where the material with low angular momentum forms a central primary protostar (CPP), whilst the material with higher angular momentum forms an accretion disc around the CPP. More rapid compression drives a stronger compression wave and delivers material more rapidly into the outer parts of the disc.