Inclination and orbital-phase-dependent resonance line-profile calculations applied to cataclysmic variable winds

Abstract

The observed properties of wind-formed resonance lines in the spectra of nova-like variables and dwarf novae in outburst, are discussed. A method is then presented of calculating inclination-and orbital-phase-dependent resonance line profiles formed in a constant-ionization wind flowing from an accretion disc centre. The particular case of the C iv /11549 line is considered. The line-transfer method used is based upon Castor's spherically symmetric application of the Sobolev approximation. The role of a wide variety of wind and disc parameters in determining the line-profile form, at both low and high inclination angles, is investigated. It is shown that the appearance of the resonance line profiles in low inclination system implies very gradual wind acceleration (reaching Voo at r>10 lo cm) and that the lack of detectable absorption in the profiles of the same lines observed at high inclinations implies that the distribution of scattering ions is distinctly bipolar. In order to explain the frequent presence of redshifted emission in the C iv/11549 line and its persistent absence in the Si ivAMOO and N v >11240 profiles, it is argued that the C 3+ ion density typically exceeds the densities of Si 3+ and N 4+ by an order of magnitude or more. This, in turn, points to M^10 _10 Moyr _1. The behaviour of the C iv 21549 line in high-inclination systems during primary eclipse is considered. It is shown that the presence of the accretion disc alone is sufficient to induce a bipolar line-emissivity distribution in the plane of the sky. However, deep line eclipses may be averted by the existence of a column of absorbing wind material located over the bright disc centre. The line eclipse light curve is found to be extremely sensitive to both the inclination angle and the ratio of the secondary star radius to the orbital radius, but rather less sensitive to the wind mass-loss rate, outflow geometry and velocity law. To resolve the predicted structure in the line eclipse light curve, a phase resolution of A0~O.OO5 is needed. Application of the eclipse calculations to IUE observations of RWTri and UXUMa again suggests a wind mass-loss rate ^10 _10 M o yr _1. ^Present address: Department of Astrophysics, South Parks Road, Oxford 0X1 3RQ.