Modelling Non-axisymmetric Bow Shocks

I present an extension of the thin layer approximation to non-axisymmetric bow shocks. By choosing a suitable set of curvilinear coordinates that matches the geometry of a generally distorted bow shock surface, I derive the fluid equations for the flow. Analytical expansions are given for the matter flow near the bow shock stagnation point. Numerical solutions are also obtained, by using a revised Runge-Kutta method. This numerical method results to be computationally stable and fast. When two winds interact, axisymmetric bow shocks are expected to form only if both winds are spherically symmetric. But stellar winds often present strong anisotropies: for all these cases a non-axisymmetric model of bow shock is required. Subject headings: hydrodynamics – methods: numerical – binaries: general – ISM: kinematics and dynamics