Hydrodynamic simulations of proplyd bow shocks

We present two-dimensional hydrodynamic simulations of the interaction betw een an ionized photoevaporation flow from a proplyd and a stellar wind from a hot star. We consider both the case of a fully supersonic wind and the c ase of a wind that passes through a global shock to become subsonic before reaching the proplyd. We compare the results of our simulations with the ob served properties of the standoff bow shocks in the Orion proplyds, finding good agreement with the supersonic case for the closer-in proplyds. This a llows the momentum flux, (M)over dotV, of the stellar wind of theta (1) Ori C to be constrained. More distant proplyds do not fit this model but may b e explained by the subsonic case, offering the prospect of using the proply ds to probe the position of the inner shock in the wind from theta (1) Ori C. Comparison of predicted silicate dust emission with published mid-infrar ed imaging provides evidence that submicron-sized grains are underabundant in the proplyd flows by an order of magnitude.