Scattering by Interstellar Dust Grains: Optical and Ultraviolet

Abstract

Scattering and absorption properties at optical and ultraviolet wavelengths are calculated for an interstellar dust model consisting of carbonaceous grains and amorphous silicate grains. Polarization as a function of scattering angle is calculated for selected wavelengths from the IR to the vacuum UV. The widely-used Henyey-Greenstein phase function provides a good approximation for the scattering phase function between ~0.4 and 1 micron, but fails to fit the calculated phase functions at shorter wavelengths and longer wavelengths. A new analytic phase function is presented. It is exact at long wavelengths, and provides a good fit to the numerically-calculated phase function for lambda > 0.27um. Observational determinations of the scattering albedo and <cos(theta)> show considerable disagreement, especially in the ultraviolet. Possible reasons for this are discussed.