PAH DESTRUCTION AROUND HOT STARS

this is a solicited proposal. the data will be made available to the community upon request to the pi one month after the data set has become available. we propose to investigate the nature of small dust particles in regions of the interstellar medium which are strongly affected by the radiation filed from nearby hot stars. such regions have shown to lack 12 micron emission in the iras data, which is currently interpreted as the destruction of small dust particles, in particular pah, in high uv fields. however, the details of the physical processes leading to pah destruction in these regions is still not well understood and very few iso observations have yet been undertaken in order to tackle this specific problem. the observations will consist of onedimensional rasters (cuts) with isocam across regions showing high color gradients in the iras data (12 to 100 microns) surrounding 3 hot stars. the targets have been selected to span the range of stellar surface temperature for which destruction is expected to take place. the cuts will be observed in all ir features attributed to small dust particles (pah, hac, qcc, ..) as well as in the nearby continuum. we will also obtain a limited number of complete cvf spectra with isocam at selected positions along the cut, in order to help interpret the filter data in terms of feature and continuum intensities. along with numerical modeling of the ir emission and radiative transfer, the obtained data should allow to discriminate between the various physical processes which have been invoked to explain the radiation driven destruction of small dust particles (e.g. photothermo dissociation, direct dissociation, colomb explosion, ..). this program will complement iso observations which have been obtained toward galactic hii regions where destruction of the small dust particles is also taking place. the geometry of the proposed regions is generally much simpler than that of galacti t [truncated!, Please see actual data for full text]