Temperature dependence of the submillimeter absorption coefficient of amorphous silicate grains

被引:105
作者
Boudet, N
Mutschke, H
Nayral, C
Jäger, C
Bernard, JP
Henning, T
Meny, C
机构
[1] Ctr Etud Spatiale Rayonnements, Toulouse 4, France
[2] Univ Sternwarte, D-07745 Jena, Germany
[3] Inst Astrophys, D-07745 Jena, Germany
[4] Max Planck Inst Astron, D-69117 Heidelberg, Germany
关键词
dust; extinction; infrared : ISM; ISM : molecules; methods : laboratory; molecular processes;
D O I
10.1086/432966
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We have measured mass absorption coefficients of amorphous silicate materials for wavelengths between 100 mu m and 2 mm (5-100 cm(-1)) and at temperatures between 300 and 10 K. For both interstellar analog MgSiO3 and simple silica SiO2, we find evidence for a strong temperature and frequency dependence. We define two distinct wavelength regimes, 500 mu m-1 mm and 100-250 mu m, for which the absorption coefficient presents different trends with frequency. To evaluate this frequency dependence, we fit our absorption coefficient using two power laws with spectral index beta that varies with temperature. We do not find a significant variation of beta with temperature between 100 and 250 mu m, whereas between 500 mu m and 1 mm a pronounced anticorrelation between T and beta exists. Globally, beta-values decrease from 2.5 to 1.5 between 10 and 300 K. This anticorrelation for interstellar analog grains has the same trend as the one observed using the balloon-borne experiment PRONAOS. We show that physisorbed water is not responsible for the observed temperature and frequency dependence and that OH groups could be at the origin of the submillimeter properties of the materials. As discussed in the literature, OH groups are often related to tunneling processes in two-level systems (TLS). In the case of the more complex MgSiO3 silicates, TLS could also be produced by the Mg+2 ions, which act as network modifiers, similar to how they act with OH groups.
引用
收藏
页码:272 / 281
页数:10
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