On the Structure of the Outer Parts of Accretion Disks in Close Binary Systems

A simple model for the outer parts of the disk in steady-state accretion is proposed in which (1) the flux emitted from the surface of the disk is due to the viscous dissipation within the disk body; (2) the tidal removal of the angular momentum occurs in the disk's outer edge which has negligibly small radial extent; (3) the energy dissipated by tidal effects is radiated exclusively from the disk's edge. The model predicts the temperature of the edge to be comparable to that of the outermost parts of the disk. The edge contributes only about 1 percent to the mean bolometric luminosity of the disk. Its contribution in the V-band, however, is much larger: about 15% at i=60° and more then 50% at i>80°. Application of this model to disks in dwarf novae implies that the crude, approximate description of tidal effects used in earlier models should be replaced with a rigid condition Rd≤Rtid. Accordingly the tidal effects are important only during outbursts.