ACCRETION DISK BOUNDARY-LAYERS IN CATACLYSMIC VARIABLES .1. OPTICALLYTHICK BOUNDARY-LAYERS

We develop numerical models of accretion disks in cataclysmic variable s (CVs), including and emphasizing the boundary layer region where the accretion disk meets the accreting white dwarf. We confine ourselves to solutions where the boundary layer region is vertically optically t hick, and find that these solutions share several common features. The angular and radial velocities of the accreting material drop rapidly in a dynamical boundary layer, which has a radial width similar to 1%- 3% of the white dwarf radius. The energy dissipated in this region dif fuses through the inner part of the disk and is radiated from the disk surface in a thermal boundary layer, which has a radial width compara ble to the disk thickness, similar to 5%-15% of the white dwarf radius . We examine the dependence of the boundary layer structure on the mas s accretion rate, the white dwarf mass and rotation rate, and the visc osity parameter alpha. We delineate the boundary between optically thi ck and optically thin boundary layer solutions as a function of these parameters and suggest that by means of a careful comparison with obse rvations it may be possible to estimate alpha in CVs. We derive an exp ression for the total boundary layer luminosity as a function of the p arameters and show that it agrees well with the luminosities of our nu merical solutions. Finally, we calculate simple blackbody continuum sp ectra of the boundary layer and disk emission for our solutions and co mpare these to soft X-ray, EUV, and He II emission-line observations o f CVs. We show that, through such comparisons, it may be possible to d etermine the rotation rates of the accreting stars in CVs, and perhaps also the white dwarf masses and the accretion rates. The spectra are quite insensitive to alpha, so the uncertainty in this parameter does not affect such comparisons.