MAGNESIUM-IRON OXIDES - ASTROPHYSICAL ORIGIN AND OPTICAL-CONSTANTS

A possible astrophysical formation process of FeO and its solid solution with MgO, called magnesiowustite (FE(x)Mg(1-x)O), is the condensation in the oxygen-rich envelopes around M stars. This process, in addition to silicate formation, is only expected under special oxygen partial pressure and on temperature conditions in an Si-poor or Fe-rich environment. For the sake of comparison with IR observations, the refractive index of laboratory-prepared magnesiowustite samples (FE(x)Mg(1-x)O, x = 1.0, 0.9, 0.8, 0.7, 0.5, 0.4) in the wavelength range from 10 to 500 mu m were calculated from reflectance spectra. For small particles in the Rayleigh limit (radius much less than lambda), the peak wavelengths of the absorption coefficient range between 20 (FeO) and 18 mu m (Fe0.4Mg0.6O).