Mid-infrared extinction coefficients of amorphous silicates |
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| Authors: | Chiyoe Koike Hiroichi Hasegawa |
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| Institution: | 1. Kyoto Pharmaceutical University, Kyoto, Japan
2. Department of Physics, Faculty of Science, Kyoto University, Kyoto, Japan
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| Abstract: | Mid-infrared extinction coefficients of five natural amorphous silicates and seven synthetic glasses were measured. Three bands at about 10, 12, and 20 μm were seen for all the measured samples. The quantities of these bands are found to have good correlations with the SiO2 content of the samples. The correlations are the most remarkable for the 10 μm band. As the SiO2 content decreases, the peak wavelengthλ m shifts to longer side, the peak heightK m decreases and the full width of half maximumW increases. A quantityλ m K m W is constant within 15%. Empirical formula $$\lambda_m (\mu m) = {11.10-2.30 x 10^-2} {SiO_2 wt.\%]} \pm 0.15$$ and $$W(\mu m) = {5.14-4.68 x 10^- 2} {SiO_2 wt.\%]} \pm 0.30$$ are obtained for the measured samples. Therefore, the correlation is present between the 10 μm peak wavelengthλ m and peak widthW for amorphous silicates. The change in peak widthW is remarkable compared the change in peak wavelengthλ m as the SiO2 content varies. For the 12 μm band the correlations with the SiO2 content are not so good. A tendency that theλ m shifts to the red and theK m lowers as the decreasing SiO2 content are found. For the samples with SiO2 content less than 50% the 12 μm band cannot recognized as the peak. For the 20 μm band, theλ m is almost independent on SiO2 content and theK m lowers with decreasing SiO2 content. The results are compared with the observed 10 μm band of the astronomical objects. A method to estimate the SiO2 content of astronomical grain materials is proposed and 48±8% SiO2 wt.% is found corresponding to the peak wavelength of 9.7 μm and the peak width of 2.5–3.0 μm of typical celestial objects. |
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