AGB winds in interacting binary stars

Models of winds from interacting binary stars are calculated. We aim at describing the outflow structure. The AGB primary star has winds driven by its pulsations and radiation pressure on dust. Time averages of both density and velocity of the winds are calculated and plotted as profiles against (i) the distance from the center of mass and (ii) the angle from the unit vector normal to the orbital plane. We find that mass is lost mainly through the outer Lagrangian point L2. This leads to an outflow structure with an increased equatorial density, which is larger in binaries with smaller orbital separation. The equator-to-pole density contrast reaches a value of 10⁵ during the Roche lobe overflow stage. The outflow develops spiral density waves at low distances from the center of mass. The spiral waves coil on themselves, approaching each other at large distances but without merging and, furthermore, they do not form a circumbinary ring in binary systems with stellar mass ratios above 0.78, if radiation on dust is taken into account. By curve fitting the two-dimensional, azimuthally averaged outflow structure, we obtained formulae that can be used in future studies as initial conditions in numerical models of common-envelope evolution and planetary nebulae formation.