MAGNESIUM-IRON OXIDES - ASTROPHYSICAL ORIGIN AND OPTICAL-CONSTANTS

A possible astrophysical formation process of FeO and its solid soluti on with MgO, called magnesiowustite (FE(x)Mg(1-x)O), is the condensati on in the oxygen-rich envelopes around M stars. This process, in addit ion to silicate formation, is only expected under special oxygen parti al pressure and on temperature conditions in an Si-poor or Fe-rich env ironment. For the sake of comparison with IR observations, the refract ive 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 t o 500 mu m were calculated from reflectance spectra. For small particl es in the Rayleigh limit (radius much less than lambda), the peak wave lengths of the absorption coefficient range between 20 (FeO) and 18 mu m (Fe0.4Mg0.6O).