Environment dependence of interstellar extinction curves.

Abstract

The IUE interstellar extinction curves published by Aiello et al. (1988) are decomposed into a bump, linear rise and FUV non-linear rise, in the parameterization scheme of Fitzpatrick & Massa (1990). The parameters of the 115 extinction curves are given. The lines of sight are characterized from the IRAS Skyflux and Point Source Catalogue data. Mean extinction curves for each of the environments are given.

The following environment specific behaviour has been found. We confirm that the linear rise is systematically less in dense media, corresponding to an accretion of their carriers on big grains in such environments. The bump is not weakened in dense media, but is sensitive to the presence of strong UV radiation fields. In HII regions we note abnormal behaviour of the bump width and a correlation of bump position and bump width. This argues against a removal of the bump carrier in HII regions by sticking to big grains.

No environment specific behaviour for the FUV non-linear rise was noted except for a weak dependence on E(B-V)/d, notably in HII regions.