The Stability of Ionization Fronts

The stability of plane strong D-type and weak R-type ionization fronts is considered, allowing for the absorption of ionizing photons in the H ii region, and assuming that the H 1 and H ii regions behave isothermally. No instabilities have been found for strong D-type ionization fronts, but weak R-type ionization fronts are moderately unstable if recombination is taken into account.