Dust Properties in the Far-Ultraviolet in Ophiuchus

We have derived the albedo (a) and phase function asymmetry factor (g) of interstellar dust grains at 1100 A using archival Voyager observations of diffuse radiation in Ophiuchus. We have found that the grains are highly forward-scattering, with g = 0.55 ± 0.25 and a = 0.40 ± 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.