Some effects of shocks in H II regions

Some possible effects of strong shocks traveling through an H II region are investigated using a theoretical model of an H II region around an O6 star in a uniform medium. The diffuse radiation field produced by H, He, and He(+) is taken into account along with collisional ionization. An expansion velocity of 200 km/s is introduced in the central parts of the model nebula to produce a shocked shell, and the subsequent hydrodynamic evolution of the nebula is followed. The results show that a modest increase in shell density can trigger recombination processes in the outer regions of the nebula.