Dynamical evolution of wind-driven H II regions in strong density gradients

The champagne model which describes the dynamical evolution of HII regions in the presence of a density discontinuity is reexamined including the effects of stellar winds. We consider stars with widely different ratios of ionizing flux to stellar wind power, as well as different distances between the star and the boundary of its parental molecular cloud. We also performed simulations with reduced cooling by suppressing thermal conduction. The evolution of the gas is followed by means of axisymmetric 2-D numerical simulations. The hot gas generated by a shocked stellar wind produces important morphological differences with respect to the windless case: the basic one is that the dense shell of swept-up gas which surrounds the bubble of hot gas reaches velocities much higher than those of the outer boundary of the champagne flow in the windless case, and the volume affected by the blowout of the HII region is accordingly much greater. Instabilities in the expanding shell are likely to make the density and velocity structure of the HII region more complex. Simulated maps of X-ray emission produced by the shocked stellar wind are presented and discussed. X-ray emission has a compact and an extended peak, both in intensity and in hardness ratio, arising from the different shock structures present inside the hot bubble. We also present maps of low frequency emission, with emphasis on the continuum emission as a tracer of emission measure and on the line-to-continuum ratio at a given frequency as a tracer of kinematic structure.