Absorbing ice model of interstellar grains

Abstract

Extinction curves have been calculated for Mie scattering by grains with a refractive index m = n - ik where n was between 1.3 and 2.0 and k varied from 0 to 0.5. A good fit for the observed interstellar extinction in the wavelength region of 0.1 to 2.0 µm was obtained for particles with radius 0.1 µm and m = 1.3 - 0.2 i. Inclusion of the changes in the refractive index in the vacuum ultraviolet region due to the strong absorptions of methane, ammonia and water does not appreciably alter these results. Theoretical extinction curves for the composite medium of H₂O, NH₃, CH₄ and graphite show a general agreement with the observed interstellar reddening curve over the whole spectral range, in addition to producing kinks in the far ultraviolet region.