1996A&A...309..258G

We redefine the term "astronomical silicate" by interpreting the 9.7µm and 18µm interstellar features not in terms of absorption by a pure silicate but rather in terms of silicate core-organic refractory mantle particles. The silicate core optical properties used are those of a glassy (amorphous) olivine produced in the laboratory. The optical constants of the organic refractory mantle material are derived from a combination of astronomical and laboratory spectra of residues of ultraviolet photoprocessed ices, which we define as ``astronomical organic refractory". The silicate core-organic refractory mantle elongated dust model provides an excellent match to the observation of the Becklin-Neugebauer object polarization features in shape, width, and in relative strength. An additional ice mantle is included on a fraction of the dust in the line of sight to the BN object which is consistent with the 3.1 µm absorption strength. This further improves the match to observations.