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The 11 micron Silicon Carbide Feature in Carbon Star ShellsSilicon carbide (SiC) is known to form in circumstellar shells around carbon stars. SiC can come in two basic types - hexagonal alpha-SiC or cubic beta-SiC. Laboratory studies have shown that both types of SiC exhibit an emission feature in the 11-11.5 micron region, the size and shape of the feature varying with type, size and shape of the SiC grains. Such a feature can be seen in the spectra of carbon stars. Silicon carbide grains have also been found in meteorites. The aim of the current work is to identity the type(s) of SiC found in circumstellar shells and how they might relate to meteoritic SiC samples. We have used the CGS3 spectrometer at the 3.8 m UKIRT to obtain 7.5-13.5 micron spectra of 31 definite or proposed carbon stars. After flux-calibration, each spectrum was fitted using a chi(exp 2)-minimisation routine equipped with the published laboratory optical constants of six different samples of small SiC particles, together with the ability to fit the underlying continuum using a range of grain emissivity laws. It was found that the majority of observed SiC emission features could only be fitted by alpha-SiC grains. The lack of beta-SiC is surprising, as this is the form most commonly found in meteorites. Included in the sample were four sources, all of which have been proposed to be carbon stars, that appear to show the SiC feature in absorption.
Document ID
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Speck, A. K.
(University Coll. London, United Kingdom)
Barlow, M. J.
(University Coll. London, United Kingdom)
Skinner, C. J.
(Space Telescope Science Inst. Baltimore, MD United States)
Date Acquired
August 17, 2013
Publication Date
October 1, 1996
Publication Information
Publication: From Stardust to Planetesimals: Contributed Papers
Subject Category
Accession Number
Distribution Limits
Work of the US Gov. Public Use Permitted.
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