Scattering by Interstellar Dust Grains. I. Optical and Ultraviolet

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 infrared to the vacuum ultraviolet. The widely used Henyey-Greenstein phase function provides a good approximation for the scattering phase function at wavelengths between ~0.4 and 1 μm but fails to fit the calculated phase functions at shorter 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 λ>0.27 μm. Observational determinations of the scattering albedo and <cosθ> show considerable disagreement, especially in the ultraviolet. Possible reasons for this are discussed.