Wind accretion in binary stars. II. Angular momentum loss

We present three-dimensional hydrodynamic calculations of mass transfer in an interacting binary system in which one component undergoes mass loss through a wind, and does so for various values of the mass ratio. The radius of the mass-losing star is taken to be half the size of its Roche lobe. Calculations are performed for gases with a ratio of specific heats γ=5/3. Mass loss is assumed to be mechanically, thermally, or radiatively driven. We compute the specific angular momentum of gas escaping the system (l_w) for these various cases. We show that l_w does not reach a value higher than ∼ 1.2 for very low wind velocities and that it reaches the limiting case of a spherically symmetric wind for large wind velocities, for mass ratio smaller or equal to 1. For larger mass ratio, however, l_w is larger than the expected limiting value. The value of l_w depends slightly on the wind mechanism which modifies the relation between the wind velocity at the surface of the star and the velocity at the Roche lobe surface. The specific angular momentum, l_w, is large enough in a wide range of velocities to imply a shrinking of the system. This makes the symbiotic channel for Type Ia supernovae a plausible one and could also help explain the existence of Barium stars and other Peculiar Red Giants with orbital periods below, say, 1000 days.