Optical Properties of Graphite-Iron-Silicate Grain Mixtures

The mean optical properties of mixtures of particles consisting of graphite, iron and silicates have been computed using the Mie theory for spherical particles. Mixtures with individual components contributing more or less equally to the optical extinction are shown to provide good fits to the observed interstellar extinction curve including the characteristic graphite feature at $${\lambda}^{-1}\,\cong 4.4\,{\mu}^{-1}$$ . The same mixtures are able to account for the observed 10 μ -silicate band in the extinction whilst also fitting the data on the diffuse galactic light at optical and ultra-violet wavelengths. Our models are also consistent with the available data on the backscattering properties of grains.