Scattering by Interstellar Dust Grains. I. Optical and Ultraviolet

Scattering and absorption properties at optical and ultraviolet wavelengthsare calculated for an interstellar dust model consisting of carbonaceous grainsand amorphous silicate grains. Polarization as a function of scattering angleis calculated for selected wavelengths from the IR to the vacuum UV. Thewidely-used Henyey-Greenstein phase function provides a good approximation forthe scattering phase function between ~0.4 and 1 micron, but fails to fit thecalculated phase functions at shorter wavelengths and longer wavelengths. A newanalytic phase function is presented. It is exact at long wavelengths, andprovides a good fit to the numerically-calculated phase function for lambda >0.27um. Observational determinations of the scattering albedo and showconsiderable disagreement, especially in the ultraviolet. Possible reasons forthis are discussed.Comment: ApJ, accepted. 19 pages, 10 figures. This version includes a new analytic scattering phase function which is an improvement on the Henyey-Greenstein phase function. Sections on X-ray scattering in previous version of this astro-ph submission have been relocated to a separate paper (Draine 2003: astro-ph/0308251