The variation of galactic interstellar extinction in the ultraviolet.

Abstract

The interstellar extinction in the UV (3.25 μm^-1 ≤ λ^-1 ≤ 8.0 μm^-1) has been determined from IUE spectra for 29 reddened early-type stars by use of the pair method. The star sample was selected on the basis of highly deviant ratios of the strength of the 4430 Å diffuse interstellar absorption feature to color excess E(B-V) (15 stars) and on the basis of association with reflection nebulae (9 stars). The incidence of peculiar extinction curves among this sample as measured by significant deviations from the mean galactic extinction law is near 70%. Correlations of peculiar extinction with cloud environments are investigated. Previous studies that show variation in UV extinction characteristics with galactic longitude or with association with specific galactic spiral arms are confirmed.