Scattering by Interstellar Dust Grains. I. Optical and Ultraviolet

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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 infrared to the vacuum ultraviolet. The widely used Henyey-Greenstein phase function provides a good approximation for the scattering phase function at wavelengths between similar to0.4 and 1 mum 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 lambda > 0.27 mum. Observational determinations of the scattering albedo and [cos theta] show considerable disagreement, especially in the ultraviolet. Possible reasons for this are discussed.