Computer Science
Scientific paper
Jun 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20159a&link_type=abstract
Spitzer Proposal ID #20159
Computer Science
Scientific paper
We propose to use the Spitzer IRS SL1 & SL2 spectrographs to observe the solid state features due to carbonaceous/PAH and silicate grains in absorption towards four stars behind the Southern Coalsack dark cloud. Our goal is to determine the composition of the small grains, by contrasting sightlines, in the same cloud, showing nominal and enhanced grain destruction. Combined optical and NIR photometry shows distinct values of the total to selective extinction (R_V) for different parts of the cloud, indicating varying grain size distributions. Together with optical, FUV and X-ray observations, the R_V measurements indicate that shock-induced grain destruction is taking place in parts of the Coalsack. By comparing the dust absorption on sightlines with and without enhanced grain destruction, and by combining these with tracers of the gas phase abundance, we can determine the composition of the small grains. The target stars have been chosen because: 1) they have well determined distances, 2) they probe only absorption by Coalsack material, 3) they have FUSE and HST/STIS (or IUE) UV and FUV data already in hand to provide gas phase abundances and extinction curves and 4) they provide two examples each of sightlines with enhanced and nominal R_V.
Andersson Bengt-Goran
McCandliss Stephan R.
Wannier Peter G.
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