Infrared emission line studies of the stucture and excitation of H II regions

Maps of five H II regions in one or more of the infrared fine-structure lines of Ne II (12.8 μm), Ar III (9.0 μm), and Si IV (10.5 μm) have been obtained with angular resolutions ranging from 4'' to 7''. The observations are used to discuss the morphology and excitation of these nebulae. Considerable diversity is found in the structures of the nebulae, probably resulting from differences in their ages and the circumstances of their formation. In all cases, more ionizing luminosity than would be provided by a single dominant ionizing star appears to be required, although uncertainties in the model nebulae make this conclusion uncertain