Search

We study the evolution of a globule of neutral material immersed in the more tenuous hotter plasma of an H iiregion surrounding newly born OB stars. The neutral globule is illuminated by the direct ionizing radiation of OB stars, and by diffuse radiation emitted by recombination in the surrounding ionized gas. We perform 2D, time dependent axisymmetric hydrodynamic simulations, and find that, for values of the diffuse field of the order of 10% of the direct field, the evolution of the globule is completely different to its evolution when the diffuse field is neglected.

The study of the dynamics of ionization fronts has moved far since Franz Kahn helped define the field in the 1950s. Nevertheless, the stability of the fronts and the nature of elephant trunks and bright rims in HII regions remain contentious issues.