The formation of protostellar disks. III. The influence of gravitationallyinduced angular momentum transport on disk structure and appearance

Hydrodynamical two-dimensional calculations are presented for the evolution of collapsing, rotating protostars, including the effects of radiative acc eleration and angular momentum transport. The initial cloud is assumed to b e a uniformly rotating centrally condensed sphere with rho proportional to r(-2). Results are presented for masses of 1, 2, and 10 M., over times comp arable to protostellar lifetimes. The calculations show how a warm, quasi-h ydrostatic disk surrounding a central unresolved core forms, grows in mass and size, and accretes onto the central object. As a result of the accretio n of material from the parent cloud, the disk is encased in one or two accr etion shock fronts, located several scale heights above the equatorial plan e. During accretion, the disks grow radially due to the effects of angular momentum transport, which according to our model arises from tidally induce d gravitational torques. In this manner, quasi-static disks in excess of se veral thousand AU in radius can be produced. Accretion onto the central obj ect slows down, however, and rather long timescales (M/(M) over dot greater than or equal to 10(7) yr) are reached while an appreciable fraction of th e total mass (approximate to 35%) is still in the disk. In order to further reduce the disk mass on a shorter timescale, processes not considered here must be invoked. Alternatively, if the initially selected angular momentum is significantly lower, smaller disk sizes would result. Frequency-depende nt radiative transfer calculations at selected ages, including the effects of scattered radiation in the infrared and optical spectral regimes, show h ow the continuum spectra of the structure depend on the disk's orientation and age and how the observed isophotal contours vary with wavelength and vi ewing angle. Because of the strong dependence on viewing angle, continuum s pectra alone should not be used to estimate the evolutionary stage of devel opment of these objects. The infrared flux at similar to 10 mu m can vary b y orders of magnitude between pole-on and edge-on views, and the inferred t otal bolometric luminosity will vary by up to a factor of greater than or s imilar to 30 as a function of viewing angle during much of the lifetime of accreting circumstellar disks. We conclude that near- and mid-infrared sear ches for disks will be strongly biased toward pole-on orientations because of this "flashlight" effect.