Why astromineralogy should care about the far-infrared range
- Autor(en)
- Thomas Posch, Harald Mutschke, Franz Kerschbaum, Nathalie Boudet
- Abstrakt
Within the next years, several satellite telescopes - among them Herschel - will make it possible to perform spectroscopic studies of dust-forming objects in the far-infrared (FIR) range. The ISO mission, carrying a midinfrared as well as an FIR spectrometer, has shown that astromineralogical studies can profit considerably from the combination of both wavelength domains. The present contribution aims at highlighting some recent results of laboratory investigations in the FIR range. Two principal effects of interest are discussed: the influence of temperature (1) on the positions of solid state bands and the corresponding band widths and (2) on the gradient of the absorption efficiency - both for selected dust species, respectively. As for the first point, we show the temperature dependence of the FIR bands of the following potential stardust minerals: calcite (CaCO3), dolomite (CaMg[CO3]2), forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Calcite, e.g., has a strong maximum of its absorption efficiency at 85.1œm (for small, spherical particles) at room temperature. This maximum shifts to 84.1œm as the temperature is reduced to 10 K. For nonspherical grain shapes, the same absorption efficiency maximum of calcite is located at other wavelengths, but the shift to smaller wavelengths with decreasing temperatures is also seen (Posch et al., in prep.). The 69 œm feature of forsterite shows a similar behaviour, while for fayalite even the emergence of new bands at cryogenic temperatures is found (cf. Posch et al. 2004). For amorphous SiO2 and amorphous MgSiO3, we examine the dependence of the gradient of the absorption efficiency Qabs in the FIR in the temperature, again based on room temperature (300 K) and cryogenic measurements (down to 10K). It is pointed out that with decreasing temperature, the slope of Qabs increases, especially in the very far infrared (beyond 250œm; see Boudet et al. 2005 for details). A similar behaviour has previously been reported for FeSiO4 by Menella et al. (1998). Both the 'band shift' and the 'Qabs-slope-change' effect permit it in principle to use future FIR obervations as means to constrain the temperatures prevailing in dusty environments. This requires careful laboratory studies to set the reference points for the respective dust thermometers. However, the strong temperature dependence of many solid state bands is not only interesting for potential 'thermometric' purposes, but may also have consequences for some current band assignments. Œ2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- Organisation(en)
- Institut für Astrophysik
- Externe Organisation(en)
- Friedrich-Schiller-Universität Jena, Institut polytechnique de Grenoble
- Journal
- Astronomische Nachrichten
- Band
- 326
- Seiten
- 584
- ISSN
- 0004-6337
- Publikationsdatum
- 2005
- ÖFOS 2012
- 103003 Astronomie
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/b1cb634b-00a0-4ca1-9e08-a6eb039d81e8