Dust, Molecular, Atomic Composition and the Physical Conditions in Molecular Clouds

Details Dust, Molecular, Atomic Composition and the Physical Conditions in Molecular Clouds Dust, Molecular, Atomic Composition and the Physical Conditions in Molecular Clouds

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992hst..prop.3759b&link_type=abstract

HST Proposal ID #3759

Physics

Hst Proposal Id #3759

Scientific paper

IRAS images of nearby molecular clouds show that the mid-IR (12 and 25um) emission, supposed to come from small particules, is distributed very differently from the 100 um emission from large grains. These variations in the IR colors probably result from variations in the abundance of the small particules. We have performed observations of clouds of different colors ("blue" and "red") in the Chamaeleon at sub-mm, visible and UV wavelengths. They show that the variations in the IR colors are accompa nied by variations in the extinction curve, in the abundance of molecules (CO, CH+), as well as in temperature and density. The observation with the GHRS of several atomic and molecular absorption lines in the spectra of stars located behind both red and blue clouds will give access to important information on the clouds : H column densities from the lines of SII, depletion processes from the Si abundance, density and temperature from lines of the different CO rotation levels, pressure independently from lines of different CI excitation levels, cooling rates and heating processes in cold and warm phases from respectively CII and OI excited levels... All these quantities compared with our models will in addition to the study of the color variations and their implications, constitute a valuable data base to understand the physics and chemistry of these molecular clouds.

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