Accretion disks in cataclysmic binaries are optically thick (in the vertical direction), except for the case of inner parts of cool disks in dwarf novae at quiescence, which are optically thin. In long period Algols disks are cool and optically thick; their atmospheres can be quite extensive.Except for inclinations close to i = 0°, disks obscure either one or both hemispheres of the central star, the obscuration being either partial or total. In particular:
(a)In stationary accretion cataclysmic binaries (old novae and nova-like systems), at inclinations close to 90° the white dwarf is fully obscured; at i < 85° only its top hemisphere becomes visible.(b)In dwarf novae at quiescence, at inclinations close to 90°, the obscuration of the white dwarf is either complete (for disk radii Rd ≥ 4 × 1010 cm), or limited to its equatorial parts (for Rd ≤ 2 × 1010 cm); at i ≈ 85 – 88° the top hemisphere becomes fully visible, while the bottom hemisphere is fully obscured; at i < 85°, due to the low optical thickness of the inner disk, parts of the bottom hemisphere near the equator also become visible.(c)In long period Algols the situations is similar as under (a); in addition, depending on inclination, part of the obscuration can be due to the atmosphere of the disk.
Non-Local Effects of Turbulence on the Excitation of Trapped Oscillations in Dwarf-Nova Accretion Disks
