THE FORMATION OF PROTOSTELLAR DISKS .2. DISKS AROUND INTERMEDIATE-MASS STARS

Hydrodynamical calculations of the evolution of a collapsing, rotating axisymmetric 10 M. molecular clump, including the effects of radiativ e acceleration but without magnetic fields, are presented. The initial cloud is assumed to be a uniformly rotating, centrally condensed sphe re with rho proportional to r(-2). Several cases are considered, in wh ich both the overall clump size and the total amount of angular moment um are varied. The calculations show how a warm, quasi-hydrostatic dis k surrounding a central unresolved core of only a few solar masses for ms and grows in size and mass. The disk is encased in two distinct acc retion shock fronts, both of which are several scale heights above the equatorial plane. At the end of the calculation of our standard case, the central unresolved region is found to have a mass of 2.7 M. and a ratio of rotational to gravitational energy of similar to 0.45, suffi ciently large to be unstable to nonaxisymmetric perturbations. In addi tion, the inner portions of the disk containing most of the mass are u nstable according to the local Toomre criterion, implying that also in this region nonaxisymmetric perturbations will lead to rapid evolutio n. Under the assumption that gravitational torques would transport ang ular momentum out of this region, a central core of less than or simil ar to 8 M. with a stable disk of greater than or similar to 2 M. shoul d result. Frequency-dependent radiative transfer calculations of the s tandard case at selected ages show how the continuum spectrum of the s tructure depends on the disk's orientation and age and how the observe d isophotal contours vary with wavelength. Because of the strong depen dence on viewing angle, continuum spectra alone should not be used to estimate the evolutionary stage of development of these objects. Compa rable results were obtained for the other cases considered.