Dust Properties in the FUV in Ophiuchus

Abstract

We have derived the albedo ($a$) and phase function asymmetry factor ($g$) of interstellar dust grains at 1100 \AA ~ using archival {\it Voyager} observations of diffuse radiation in Ophiuchus. We have found that the grains are highly forward scattering with $g =$ 0.55 $\pm$ 0.25 and $a =$ 0.40 $\pm$ 0.10. Even though most of the gas in this direction is in the Ophiuchus molecular cloud, the diffuse FUV radiation is almost entirely due to scattering in a relatively thin foreground cloud. This suggests that one cannot assume that the UV background is directly correlated with the total amount of gas in any direction.