He II lines from cataclysmic variable winds.

Abstract

We present the first quantitative examination of the contribution of the stellar winds in high accretion rate, non-magnetic cataclysmic variables to the He II λ1640 and λ4686 lines. The line profiles are simulated with the Sobolev approximation using level populations taken from previous NLTE calculations which matched the observed strengths of the C IV and N V UV resonance lines. We find that these models can reproduce the strength and shape of the blueshifted absorption seen in the He II λ1640 line in lUE spectra for low-inclination systems. When viewed at high inclinations, models with a bipolar density distribution produce single-peaked emission lines, as observed. These can account for significant fractions of the luminosities of He II λ1640 and λ4686 observed in the high-inclination systems. In terms of equivalent widths the contribution is less, but this may be due to inadequate modelling of the continuum rather than of the lines. The calculated line profile for He II λ4686 is very similar to that observed and is also strongly eclipsed, as required. Similarities in the orbital phasing of the radial velocity variations of this line and the UV resonance lines are noted. The possible wind contribution to the Balmer lines is also discussed.