Photoionization Models for the Wind from TW VIR

Abstract

One of the outstanding features of the UV spectra from dwarf novae when viewed during outburst, and from many other cataclysmic variable (CV) stars, is the existence of P-Cygni type profiles in the resonance lines of C IV, Si IV, and N V (e.g. Heap et al. 1978; Szkody 1981, 1982). Profiles of this type are familiar from the study of 0 and B stars; in these stars P-Cygni profiles are due to scattering by material in a stellar wind. If the line profiles from dwarf novae are compared to those from 0 and B stars, it is found that the line shapes are similar in the two classes of objects, but that the line strengths differ. The line strengths depend on the abundances of the scattering ions, and hence on the physical conditions in the wind. For example, if the abundances of the ions in the CV winds are determined by the rate of photionization by the local continuum radiation, then the observed UV line strengths can be used to constrain the flux in the radiation field.