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Astron. Astrophys. 329, 1035-1044 (1998)

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Silicon carbide and the 11.3-µm feature

Renaud Papoular 1, Michel Cauchetier 1, Sylvie Begin 2 and Gerard LeCaer 2

1 CEA/SPAM, CE Saclay, F-91191 Gif-sur-Yvette Cedex, France
2 Laboratoire Sc. Genie, Materiaux Metalliques, Ecole des Mines, F-54042 Nancy Cedex, France

Received 11 April 1997 / Accepted 21 July 1997

Abstract

We have synthesized crystalline SiC powders and obtained their IR extinction spectra when embedded in KBr and CsI matrices. These spectra are not compatible with purely spherical grains. By contrast, they quantitatively support the assumptions that 1) the bulk optical constants of the grains are identical with those of thin films, and very nearly independent of crystal polytype, as measured by Spitzer et al. (1959) and 2) the granulometry is a continuous distribution of ellipsoids. All of this also applies to previously published laboratory SiC spectra.

Within this framework, we can predict the spectra of the same powders if freely suspended in vacuum. Finally, using linear combination of these, it is possible to closely fit the various spectral shapes exhibited by the IRAS/LRS data for C-rich stars.

Key words: methods: laboratory – stars: carbon – stars: circumstellar matter – infrared: stars

Send offprint requests to: R.Papoular

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© European Southern Observatory (ESO) 1998

Online publication: December 16, 1997
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