Interaction between a stellar wind and an accretion flow

Hydrodynamic calculations on the interaction between a wind from an astronomical object and an axisymmetric accretion flow are performed by solving the inviscid Euler equation. The numerical method employed is the implicit Osher upwind scheme with second-order accuracy. It is found that a supersonic bubble bounded by a bullet-shaped shock is formed around the body if the gas pressure on the body surface is sufficiently high. An astropause, which is a contact surface formed between the wind gas and the incoming gas, is found to be unstable when such a bubble is formed. When the surface pressure is lowered or the Mach number of the incoming flow is raised beyond some critical value, the wind terminates abruptly. In the transition stage very unsteady flow are observed. (author)