1996A&A...313L...5R

The [Fe II] and [Fe III] emission of seven galactic H II regions is studied with the aim of comparing their gaseous Fe abundance. The [Fe II] line intensity ratios are found to behave in a manner that suggests fluorescence effects. In addition, the uncertainty in the physical conditions and the ionization stratification of the layers where [Fe II] emission arises, contribute to render the total Fe abundance implied by these lines unreliable. The Fe/O abundance ratios are consequently calculated using the [Fe III] lines and ionization correction factors derived from the photoionization models available, and are found to be 3 to 30 times lower than the solar value. The close correlation found between these Fe abundances and the ionization degree suggests that the local UV radiation field, while determining the ionization equilibrium, also affects the structure and composition of dust grains coexisting with the H II gas, thereby releasing Fe gas to the observed extent.