Measurement of Dust Optical Properties in Coalsack

TL;DR

This study measures the optical properties of dust grains in the Coalsack Nebula using FUSE and Voyager data, providing key parameters like albedo and phase function asymmetry consistent with prior work and theory.

Contribution

It presents new measurements of dust optical constants in the Coalsack Nebula using space-based observations, confirming previous values and clarifying the scattering sources.

Findings

Albedo is approximately 0.28 with a 0.04 uncertainty.

Phase function asymmetry factor is about 0.61 with a 0.07 uncertainty.

Diffuse emission is mainly due to nearby hot stars scattering light, not background clouds.

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 $0.28 \pm 0.04$ and the phase function asymmetry factor with a value of $0.61 \pm 0.07$ throughout the spectral range from 900 -- 1200 \AA, 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.