Far-infrared spectra of hydrous silicates at low temperatures - Providing laboratory data for Herschel and ALMA - AstrophysicsReport as inadecuate




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Abstract: Hydrous silicates occur in various cosmic environments, and are among theminerals with the most pronounced bands in the far infrared FIR spectralregion. Given that Herschel and ALMA will open up new possibilities forastronomical FIR and sub-mm spectroscopy, data characterizing the dielectricproperties of these materials at long wavelengths are desirable. We aimed atexamining the FIR spectra of talc, picrolite, montmorillonite, and chamosite,which belong to four different groups of phyllosilicates. We tabulatedpositions and band widths of the FIR bands of these minerals depending on thedust temperature. By means of powder transmission spectroscopy, spectra of theexamined materials were measured in the wavelength range 25-500 mum attemperatures of 300, 200, 100, and 10 K. Room-temperature measurements yieldthe following results. For talc, a previously unknown band, centered at 98.5mum, was found, in addition to bands at 56.5 and 59.5 mum. For montmorillonite,several bands at wavelengths <110 mum were detected, including a band at 105mum with an FWHM of about 10 mum. Picrolite shows a sharp 77 mum FIR band.Chamosite is characterized by bands in the 72-92 mum range, and a prominentband at 277 mum. At decreasing temperature, most of the bands shift to shorterwavelengths. Examining a potential counterpart of the 105mum band in thespectra of HD 142527 and HD 100546, we find that the broad band in the spectraof these young stars - extending from 85 to 125 mum - cannot be due tomontmorillonite or any of the hydrous silicates we studied, since thesematerials have sharper bands in the FIR wavelength range than previouslyassumed, especially at low temperatures.



Author: H. Mutschke 1, S. Zeidler 1, Th. Posch 2, F. Kerschbaum 2, A. Baier 2, Th. Henning 3 1 Astrophysikalisches Institut, Jena, German

Source: https://arxiv.org/







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