2–16 μm spectroscopy of micron-sized enstatite (Mg,Fe)2Si2O6 silicates from primitive chondritic meteorites |
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| Authors: | J E Bowey A Morlok † M Köhler M Grady |
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| Institution: | Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT;Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD;Institut für Planetologie, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany;PSSRI, The Open University, Walton Hall, Milton Keynes MK7 6AA |
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| Abstract: | We present mid-infrared spectra from individual enstatite silicate grains separated from primitive type 3 chondritic meteorites. The 2–16 μm transmission spectra were taken with microspectroscopic Fourier-transform infrared (FT-IR) techniques as part of a project to produce a data base of infrared spectra from minerals of primitive meteorites for comparison with astronomical spectra. In general, the wavelength of enstatite bands increases with the proportion of Fe. However, the wavelengths of the strong En100 bands at 10.67 and 11.67 decrease with increasing Fe content. The 11.67-μm band exhibits the largest compositional wavelength shift (twice as large as any other). Our fits of the linear dependence of the pyroxene peaks indicate that crystalline silicate peaks in the 10-μm spectra of Herbig AeBe stars, HD 179218 and 104237, are matched by pyroxenes of En90−92 and En78−80, respectively. If these simplistic comparisons with the astronomical grains are correct, then the enstatite pyroxenes seen in these environments are more Fe-rich than are the forsterite (Fo100) grains identified in the far-infrared which are found to be Mg end-member grains. This differs from the general composition of type 3 chondritic meteoritic grains in which the pyroxenes are more Mg-rich than are the olivines from the same meteorite. |
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| Keywords: | circumstellar matter infrared: stars |
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