The following document lists the file abstract/MGIARD_WDUSTHII.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
The aim of this proposal is to observe the behaviour of the 6.2 and 7.7 mu dust features, and the underlying continuum emission, in the direction of a well defined edge-on ionization front. This will allow to derive new constrains on the nature of the emitting particles, PAH molecules or large carbonaceous grains. Ground based observations have shown that the associated 3.3, 11.3, and 8.6 mu features, generally attributed to C-H peripheral bonds on the same particles, are abundant in the photo-dissociation region and absent from the HII gas, with a marked transition at the precise location of the ionization front. This proves that the particular physical conditions in the HII region, either modify the nature of the emitting particles (eg ionization or de-hydrogenation) or destroy them (eg photo- thermodissociation of PAHs or H+ chemisputtering of small carbonaceous grains). In the first hypothesis, the 6.2 mu and 7.7 mu features, which are attributed to vibrational modes of the carbon skeleton, should survive, and will not show the same behaviour as the C-H features. This can be tested by imaging an ionization front, M17-SW (Autumn launch) or Orion bar (Spring launch), with ISO-CAM in the filters dedicated to the 6.2 and 7.7 PAH features. The transition of the 3.3 mu feature has been observed to occur in a very sharp region, about 2 arcsec, so that the full angular resolution of the camera is needed : 1.5" per pixel (3" resolution).