I review the basic properties of interstellar extinction in the Milky Way galaxy, focusing primarily on the wavelength dependence within the IR through UV spectral region. My primary goal is to review the evidence supporting the idea that Galactic extinction curves can be considered a 1-parameter family characterized by their value of RV ≡ AV/E(B-V). Based on analysis of new (i.e., 2MASS) and old (i.e., IUE) data for ̃100 sightlines, I show that the UV, optical, and IR wavelength regimes do display coherent variations, but with too much intrinsic scatter to be considered truly correlated. A 1-parameter family can be constructed which illustrates these broad trends, but very few individual sightlines are actually well-reproduced by such a family and disagreement with the mean trends is not a sufficient condition for ``peculiarity.'' Only a very small number of extinction sightlines stand out as truly peculiar. It is likely that simple variations in the mean grain size from sightline to sightline are responsible for much of the coherent variability seen in Galactic extinction, and might also explain the ``peculiar'' extinction long-noted in the Magellanic Clouds.
Astrophysics of Dust
- Pub Date:
- May 2004
- Invited review at the Astrophysics of Dust 2003 Symposium held in Estes Park, Colorado, USA in May 26-30, 2003. Conference proceedings to be published through the ASP Conference Series in 2004, edited by A. Witt, B. Draine, and G. Clayton. 24 pages, including 14 figures