Stability Analysis of Bow Shocks

We present a linear stability analysis of bow shocks created by the interaction of a spherical wind moving with respect to its surrounding medium. The bounding shocks are assumed isothermal and with Mach number M = ∞. Following Soker, we study the evolution of short-wavelength perturbations. We find that the motion is unstable in this limit. Moreover, the ratio of the wind velocity υW to the star velocity υ* characterizes the stability properties. Bow shocks with fast winds for which υ*/υW ≪ 1 are more stable than bow shocks with slow winds, i.e., υ*/υW≫ 1.