Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26as..112..143h&link_type=abstract
Astronomy and Astrophysics Supplement, v.112, p.143
Astronomy and Astrophysics
Astrophysics
86
Dust, Extinction, Infrared: Stars, Ism: Lines And Bands, Circumstellar Matter, Stars: Agb: Post-Agb, Methods: Laboratory
Scientific paper
In this paper, we present the optical properties of a series of well-characterized metal oxides (Fe_x_ Mg_1-x_O, x=1.0, 0.9, 0.8, 0.7, 0.5, 0.4) in the wavelength range from 200nm to 500μm. A number of oxygen-rich stars show circumstellar dust features between 10 and 14μm and around 19μm which cannot be explained by ordinary cosmic silicates but may be modelled by a mixture of aluminium oxide and iron-magnesium oxides. Calculated absorption spectra for small spheres show one vibrational band in the range from 19.9μm (FeO) to 17.7μm (Fe_0.4_ Mg_0..6_O) in the Rayleigh limit. The absolute peak values of the oxide absorption bands are more than a factor of two larger than the 18μm band of amorphous silicates, indicating that a small admixture of oxides can change the 18μm/10μm band ratio dramatically. The near-infrared opacity of the iron-rich oxides is of comparable magnitude to that of Fe_3_ O_4_. Therefore, small amounts of iron-rich oxides in addition to silicates raise the absorbance in this spectral range in a very efficient way.
Begemann B.
Dorschner Johann
Henning Th
Mutschke Harald
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