DUST PROPERTIES OF CIRRUS HEATED BY B-STARS

we want to determine the infrared spectrum of the diffuse ism with lws, pht, and sws by observing a sample of cirrus clouds heated by nearby main sequence bstars. these observations offer the unique opportunity to obtain grating spectra of cirrus over the whole iso wavelength range (2.5200 micron). our selection of b type stars is based on the bright star catalog and include different spectral types ranging from b0 to b9.5. this study has several advantages when compared to observations of quiescent diffuse clouds. firstly, model parameters such as distance, radiation field, uv and optical extinction are accurately known from previous observations. secondly, the interstellar radiation field has a spectrum similar to that of a b5 star, consequently by observing different spectral types we can study variations in both the strength as well as hardness of the uv field in comparison with isrf conditions. thirdly, and most importantly, we can provide a spectroscopic signature of dust in the diffuse ism. in addition, the spectra will also yield the strengths of the important cooling lines, providing a description of the heating and cooling of the gas in our targets. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]