Structure and appearance of winds from supercritical accretion disks

Supercritical disk accretion is studied from the standpoint of vertical structure and observational appearance of the disk. Both the vertical and radial disk structure equations are derived from the steady-state fluid equations with viscosity and radiation transport included. The vertical equations with outward flow of the wind are then solved with the Henyey technique. It is found that the transition from subcritical to supercritical disk accretion is accompanied by the establishment of a very extended envelope with a high mass-low rate. The envelope usually engulfs the entire disk and perhaps a companion star if the accretion occurs in a binary system. Its appearance is essentially that of a supergiant star. The exact results are unfortunately rather sensitive to the assumed viscosity law, unlike subcritical disk structure. Two parameters are of interest in these models: the local accretion rate M, which may vary with radius in the disk because of mass loss and the critical radius r/sub c/, which is the largest radius in the disk where supercritical energy generation takes place for a given total accretion rate M/sub T/. A partial parameter study is performed to examine the behavior of the envelope as M and r/sub c/ are changed. A tendency toward dynamical instability is found for disks with small critical radii at all times during supercritical accretion. In addition, all disks appear to be dynamically unstable for a brief period when transition from subcritical to supercritical accretion takes place. The symbiotic stars may be an example of stable supercritical accretion, as Bath has originally suggested. Quantitative agreement is found between these results and the properties of symbiotic stars and a self-consistent model is constructed for these objects