Astron. Astrophys. 343, 933-938 (1999)

Infrared spectra of meteoritic SiC grains

A.C. Andersen ¹, C. Jäger ², H. Mutschke ², A. Braatz ^2,3, D. Clément ², Th. Henning ², U.G. Jorgensen ¹ and U. Ott <sup>3

1</sup> Copenhagen University Astronomical Observatory, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark (anja/uffegj@stella.nbi.dk)
² Astrophysical Institute and University Observatory (AIU), Schillergässchen 3, D-07745 Jena, Germany (conny/mutschke/braatz/dacapo/henning@astro.uni-jena.de)
³ Max-Planck-Institut for Chemistry, Becherweg 27, D-55128 Mainz, Germany (braatz/ott@mpch-mainz.mpg.de)

Received 15 July 1998 / Accepted 1 December 1998

Abstract

We present here the first infrared spectra of meteoritic SiC grains. The mid-infrared transmission spectra of meteoritic SiC grains isolated from the Murchison meteorite were measured in the wavelength range 2.5-16.5 µm, in order to make available the optical properties of presolar SiC grains. These grains are most likely stellar condensates with an origin predominately in carbon stars. Measurements were performed on two different extractions of presolar SiC from the Murchison meteorite. The two samples show very different spectral appearance due to different grain size distributions. The spectral feature of the smaller meteoritic SiC grains is a relatively broad absorption band found between the longitudinal and transverse lattice vibration modes around 11.3 µm, supporting the current interpretation about the presence of SiC grains in carbon stars. In contrast to this, the spectral feature of the large ( 5 µm) grains has an extinction minimum around 10 µm. The obtained spectra are compared with commercially available SiC grains and the differences are discussed. This comparison shows that the crystal structure (e.g., -SiC versus -SiC) of SiC grains plays a minor role on the optical signature of SiC grains compared to e.g. grain size.

Key words: infrared: ISM: lines and bands ISM: lines and bands ISM: dust, extinction stars: carbon stars: atmospheres stars: abundances

Send offprint requests to: Anja C. Andersen

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Contents

• 1. Introduction
• 2. The extraction procedure
• 3. Spectroscopy
  • 3.1. Measurement procedures
  • 3.2. Results
  • 3.3. Size effects
  • 3.4. Comparison with - and -SiC samples
• 4. Summary and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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