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Astron. Astrophys. 345, 187-202 (1999)


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Infrared properties of SiC particles

H. Mutschke 1, A.C. Andersen 2, D. Clément 1, Th. Henning 1 and G. Peiter 3

1 Astrophysikalisches Institut und Universitäts-Sternwarte (AIU), Schillergäßchen 3, D-07745 Jena, Germany
2 Astronomisk Observatorium, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark
3 Institut für Physikalische Chemie, Lessingstraße 10, D-07743 Jena, Germany

Received 25 November 1998 / Accepted 15 February 1999

Abstract

We present basic laboratory infrared data on a large number of SiC particulate samples, which should be of great value for the interpretation of the 11.3 µm feature observed in the spectra of carbon-rich stars. The laboratory spectra show a wide variety of the SiC phonon features in the 10-13 µm wavelength range, both in peak wavelength and band shape. The main parameters determining the band profile are morphological factors as grain size and shape and, in many cases, impurities in the material. We discovered the interesting fact that free charge carriers, generated e.g. by nitrogen doping, are a very common characteristics of many SiC particle samples. These free charge carriers produce very strong plasmon absorption in the near and middle infrared, which may also heavily influence the 10-13 µm feature profile via plasmon-phonon coupling.

We also found that there is no systematic dependence of the band profile on the crystal type ([FORMULA]- vs. [FORMULA]-SiC). This is proven both experimentally and by theoretical calculations based on a study of the SiC phonon frequencies. Further, we give optical constants of amorphous SiC. We discuss the implications of the new laboratory results for the interpretation of the spectra of carbon stars.

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

Send offprint requests to: mutschke@astro.uni-jena.de

© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999

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