Ultraviolet Spectra of Cataclysmic Variable Accretion Disks with NonsteadyT(r) Laws

Abstract

An extensive grid of synthetic mid- and far-ultraviolet spectra for accretion disks in cataclysmic variables has been presented by Wade & Hubeny. In those models, the disk was assumed to be in steady state; that is, Teff(r) is specified completely by the mass MWD and radius RWD of the accreting white dwarf star and the mass transfer rate , which is constant throughout the disk. In these models, Teff(r) ∝ r-3/4, except as modified by a cutoff term near the white dwarf. Actual disks may vary from the steady state prescription for Teff(r), however, as a result of, for example, outburst cycles in dwarf novae ( not constant with radius) or irradiation (in which case Teff in the outer disk is raised above Tsteady). To show how the spectra of such disks might differ from the steady case, we present a study of the ultraviolet (UV) spectra of models in which power-law temperature profiles Teff(r) ∝ r-γ with γ < are specified. Otherwise, the construction of the models is the same as in the Wade & Hubeny grid, to allow comparison. We discuss both the UV spectral energy distributions and the appearance of the UV line spectra. We also briefly discuss the eclipse light curves of the nonstandard models. Comparison of these models with UV observations of nova-like variables suggests that better agreement may be possible with such modified Teff(r) profiles.