The accretion of supergiant wind material onto the hot companion in zeta Aurigae binaries.

Abstract

This paper is an attempt to interpret the behaviour of the high excitation C IV and Si IV resonance lines in the course of a period of the Zeta Aurigae binary systems. Three distinct phenomena have been observed: shock front emission, accretion wake absorption and accretion disc emission. At the C IV and Si IV emission regions the electron temperature lies between 50000 and 80000K. The shock front electron density is of the order of 10⁸ to 10⁹cm^-3, while N_e is probably of the order of 10¹⁰cm^-3 at the rotating disc where part of the wind material has been captured by the accreting star. The authors deal with an accretion shock where the shock cone angle is large (β ≈ 25 - 45°) even when the Mach number is very large, because the accreting material is heated by its passage through the shock front. The gas inside the cone is hot enough for the existence of C³⁺ and Si³⁺ ions. The density in the accretion wake is 10⁷ to 10⁸cm^-3 - more than an order of magnitude denser than in the surrounding stellar wind.