1994A&A...289..559L

We study the dynamical evolution of a neutral globule illuminated by the ionizing radiation of OB stars. We can reproduce the main morphological and dynamical properties of cometary globules (CGs), which are rather insensitive to initial and boundary conditions. We present results of 2-d hydrodynamical simulations of the evolution of cometary globules. We present a detailed evolutionary sequence from the cloud's collapse to the quasi-stationary cometary regime. This latter phase lasts approximately 90 % of the cloud's lifetime. From the results of the simulations, we generate maps of emission measure, projected density and position-velocity diagrams, which can be confronted to optical or molecular line observations. The maps of emission measure exhibit a striking resemblance to various types of CGs and other bright-rimmed structures found in HII regions. A simple analytic model parallels and extends our simulations, including non-thermal pressure support. We derive criteria for the stability of the ionization front in the cometary phase and illustrate them with results from the simulations. We also study the gravitational stability of CGs; we find that they are stable and mainly supported by the magnetic field.