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Published online by Cambridge University Press: 12 April 2016
Accretion disks are invoked in a variety of astrophysical settings, ranging from stellar-mass black holes to active galactic nuclei. There is now little doubt that true accretion disks can also occur in binaries containing non-degenerate stars (Peters 1980; Plavec et al. 1984; Polidan 1987). In this paper, I will discuss some of the properties of disks observed photometrically in the long-period systems KU Cyg and RZ Oph.
The most intensively-studied disks are of course those in cataclysmic binaries. Accretion disks in such binaries are thought to have the classical ′alpha′ structure of Shakura and Sunyaev (1973), in which viscous dissipation arising from differential rotation converts gravitational potential energy to thermal energy in supplying the disk luminosity. This physical process requires that the viscous time scale be comparable to the radiative decay time of the disk (Pringle 1981). Most of the disk′s volume is optically thick, so disk luminosity is estimated by integrating black-body or stellar atmospheric fluxes over the disk (see Kriz and Hubeny 1986 for qualifications).