Computer Science
Scientific paper
Jul 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt........21c&link_type=abstract
Thesis (PHD). THE UNIVERSITY OF ROCHESTER , Source DAI-B 58/09, p. 4868, Mar 1998, 172 pages.
Computer Science
1
White Dwarf, Radial Viscous Force
Scientific paper
We have studied three attributes of the boundary layer (BL) between the accretion disk and the white dwarf in a cataclysmic variable. First, we have considered the effects of the radial viscous force on the structure and BL continuum emission. We find that, for models in which the radial viscous force assists the pressure gradient in resisting the infall of the accreting material, the distance from the surface of the star to the maximum in the angular velocity is significantly larger than in models which neglect this force. The much larger region in the inner disk in which the accretion energy is emitted radiatively is largely the same in the two types of models, as is the continuum emission. We have also compared models created by employing a constant electron-scattering opacity with those constructed with a realistic, tabulated Rosseland-mean opacity. We find that while the central disk temperature is greater in the latter models, the continuum spectrum is unchanged. Finally, we have performed a linearized perturbation analysis of the disk and BL. In the BL, for the case of large-scale, azimuthal oscillations, we find a triplet of torsional modes consisting primarily of a perturbation of the azimuthal velocity, and a singlet mode consisting primarily of a pressure perturbation. Two of these, which we call the 'fast torsional modes,' have rise times of enough for significant amplification of a perturbation entering the BL. They are gravity modes, modified by the large shear and radial acceleration in the BL. The instability is caused by the increase in the inertial force experienced by a parcel of accreting material with a perturbed velocity. The two fast torsional modes have frequencies close enough in magnitude to produce beating. The beat frequency spans a range from Ω up to an order of magnitude larger than that, i.e., ~20 s to (2-3) × 100 s, in the region of the boundary layer where the effective temperature has its maximum; The modulating oscillations of the fast torsional modes have much smaller periods, ~1 s. The beat oscillations between the fast torsional modes have attributes similar to the quasi-periodic oscillations observed in some cataclysmic variables.
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