Measurement of Dust Optical Properties in Coalsack Nebula

Abstract

We have used FUSE and Voyager observations of dust-scattered starlight in the neighborhood of the Coalsack Nebula to derive the optical constants of the dust grains. The albedo is consistent with a value of 0.28 ± 0.04, and the phase function asymmetry factor with a value of 0.61 ± 0.07, throughout the spectral range from 900–1200 Å, in agreement with previous determinations as well as theoretical predictions. We have now observed two regions (Ophiuchus and Coalsack) with intense diffuse background radiation and in both cases have found that the emission is due to light from nearby hot stars scattered by a relatively thin foreground cloud, with negligible contribution from the background molecular cloud.