The ionization state of the winds from cataclysmic variables without classical boundary layers

Abstract

We have calculated a grid of detailed photoionization models for the stellar winds in non-magnetic cataclysmic variables. In the light of evidence which questions the existence of a classical hot, luminous boundary layer we investigate (i) models with cool, luminous boundary layers or (ii) models with no boundary layer at all, but with a moderately enhanced accretion rate in the disc. The ionization state predicted by these models is compared with that deduced from observations of the UV resonance lines in low-inclination nova-like variables. We find that the observed strength of the C IV and N v lines can be matched by models with luminous, cool boundary layers or with disc-only models where the accretion rate is 2 - 4 x 10 exp -8 solar mass/yr. The softer radiation field means that the required wind mass loss rates are only about 6 x 10 exp -10 solar mass/yr, i.e. only a few per cent of the accretion rate, in which case radiation pressure would be a viable mechanism for driving these winds.