Balmer Line Emission Profiles from Cataclysmic Variable Accretion Disk Chromospheres

Abstract

Stark-broadened, emisson-line profiles are computed for physical conditions extant in the chromospheres of cataclysmic variable accretion disks. These calculations follow the methods of Lin, Williams, & Stover, except that our results span the lower electron number density range of 12 ≤ log ne (cm-3) ≤ 14. The rationale for high Balmer line optical depths at accretion disk faces caused by photoionization from a source in the vicinity of the white dwarf is outlined; then a series of models based on accurate absorption line coefficients is computed. Stark-broadened line widths of up to several Doppler widths are found. These pressure-broadened profiles are enough to smear the classic double-cusped line profile significantly for chromosphere temperatures of ~10,000 K, which are at the high end of those considered by Lin and coworkers. Emission-line profiles with greatly smoothed cusps result in all cases except in nearly edge-on systems, where the mass accretion rate drops below 10-10 M☉ yr-1 or where the accretion disk outer radii are less than 1010.5 cm. These results are insensitive to the shape of the boundary layer energy distribution.