Imaging spectrophotometry at a spectral resolution lambda / Delta lambda = 40-50 made with the ISOCAM circular variable filter in the spectral range 5.15 to 16.5 microns will be presented. It concerns the reflection nebula NGC 7023, the interface HII--region/molecular cloud M 17, and the star--forming regions NGC 7538 and W 3; the latter observations are still unpublished. If the radiation field is low, the mid--IR emission in the neutral interstellar medium is dominated by the emission bands and a continuum from Polycyclic Aromatic Hydrocarbons (PAHs). However, emission by very small grains dominates at 15 microns when the radiation field is higher than 10^4 times that in the vicinity of the Sun, and at 6 microns when it is 10^5 times higher. A number of embedded sources have been seen in these observations. Absorption features in their spectra reveal several molecules adsorbed on the surface of grains. The data base obtained in these observations is of high importance for interpreting mid-infrared observations of galaxies.
Joint European and National Astronomical Meeting
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