Interstellar Abundances, Depletions and Extinction

U. J. Sofia

Interstellar dust doesn't get much respect. Astronomers love to hate it, and even popular literature maligns it (e.g., an article about dust in the March 2004 issue of National Geographic reports "Space isn't empty. It's full of schmutz."). One reason for dust's lackluster reputation is the widely held misconception that we understand it and we know how to correct for its extinction effects. We do not.

I will present results from a collaborative, primarily space-based effort that has the ultimate goal of characterizing the extinction associated with different types of dust (physical conditions). The three contributing programs are: 1) to observationally determine the chemical and physical compositions of dust through abundance studies, 2) to find extinction as a function of wavelength (FUV through IR) along lines of sight that sample various physical conditions, and 3) to relate the dust composition and extinction through radiative transfer models. The good news is that we are making progress; the bad news is that we understand dust much less than we did when we started.