The following document lists the file abstract/AZAVAGNO_AZAV_HII.abs
from catalogue VI/111.
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The aim of this proposal is to use ISOCAM to study the distribution of Unidentified InfraRed Bands (UIRBs) carriers in compact Galactic HII regions. Polycyclic Aromatic Hydrocarbon (PAH) molecules are thought to be these carriers, responsible of a serie of bands observed in the infrared between 3 and 20 microns. The idea is to study the evolution of the carriers composition (size, dehydrogenation) and distribution (excitation/destruction) with the properties of the considered HII regions (spectral type of the exciting star, evolutionary stage). A previous work (Zavagno et al., 1992) has shown that the emission in the 7.7, 8.6 and 11.3 micron bands can account for 50% of the 12 micron flux in compact HII regions. Only few very bright HII regions (Orion Bar, Bregman et al., 1989,, ApJ 344, 791 - Geballe et al., 1989, ApJ 341, 278) have been observed from the ground. Presently, it is not clear to know how that dust is exactly distributed in classical compact HII regions. Can those molecules survive in the ionized medium and if so, how their spatial distribution looks like in it? How far is the extension of that dust component behind the ionization front? Answer those questions requires the ISOCAM sensitivity in UIRB filters. Such studies cannot be leaded from the ground due to the poor sensitivity of the available cameras in such filters. We have selected a sample of 8 compact visible HII regions for which the spectral type of the exciting star and the distance are known and for which visible and radio data are available in order to link the observed properties of these bands carriers to the physical properties of the ionized region.