Accretion disk boundary layers in cataclysmic variables. 1: Optically thick boundary layers

Details Accretion disk boundary layers in cataclysmic variables. 1: Optically thick boundary layers Accretion disk boundary layers in cataclysmic variables. 1: Optically thick boundary layers

Mar 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...442..337p&link_type=abstract

The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 442, no. 1, p. 337-357

Astronomy and Astrophysics

Astrophysics

115

Accretion Disks, Black Body Radiation, Boundary Layers, Cataclysmic Variables, Luminosity, Mathematical Models, Optical Thickness, White Dwarf Stars, Angular Momentum, Angular Velocity, Energy Distribution, Mass Flow Rate, Opacity, Radiative Transfer

Scientific paper

We develop numerical models of accretions disks in cataclysmic variables (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 thick, 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 approximately 1%-3% of the white dwarf radius. The energy dissipated in this region diffuses through the inner part of the disk and is radiated from the disk surface in a thermal boundary layer, which has a radial width comparable to the disk thickness, approximately 5%-15% of the white dwarf radius. We examine the dependence of the boundary layer structure on the mass accretion rate, the white dwarf mass and rotation rate, and the viscosity parameter alpha. We delineate the boundary between optically thick and optically thin boundary layer solutions as a function of these parameters and suggest that by means of a careful comparison with observations it may be possible to estimate alpha in CVs. We derive an expression for the total boundary layer luminosities as a function of the parameters and show that it agrees well with the luminosites of our numerical solutions. Finally, we calcuate simple blackbody continuum spectra of the boundary layer and disk emission for our solutions and compare these to soft X-ray, EUV, and He II emission-line observations of CVs. We show that, through such comparisons, it may be possible to determine 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.

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