Optical Properties of Glassy Bronzite and the Interstellar Silicate Bands

Abstract

Observations of broad and structureless bands at 10 and 20 µm wavelengths in the spectra of many infrared sources gave rise to extensive laboratory work on amorphous silicates supposed to be responsible for these bands (for a recent review see, e.g., Dorschner and Henning, 1986). Up to now, no experimentally manufactured silicates have been presented that could satisfactorily reproduce the large width of the bands observed in the cosmic sources or explain the observed infrared spectra over a broad wavelength interval. Consequently, a number of attempts has been made to evaluate realistic optical properties for cosmic silicates either by modifying experimental results in such a way that the observations could be more satisfactorily described (Jones and Merrill, 1976; Papoular and Pégourié, 1982; Pégourié and Papoular, 1985; Rowan-Robinson, 1986) or by combining astronomical observations, experimental data, and theoretical relations (Draine and Lee, 1984; Henning et al., 1983).