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S. Kwok (University of Calgary)
Infrared spectroscopic observations of the circumstellar envelopes of AGB and post-AGB stars have identified a variety of inorganic grains, including amorphous silicates, crystalline silicates, silicon carbide, carbonates, corundum, spinels, and possibly rutiles. Isotopic studies of meteorites have also identified similar species of presolar origin (Bernatowicz et al.~1987, Nature, 330, 728; Nittler et al.~1997, ApJ, 483, 475). These grains therefore represent an important link between stars and the solar system.
The existence of aromatic and aliphatic features and their associated plateau continuum suggests that organic compounds in solid-state form are also made during the post-AGB phase of stellar evolution (Kwok et al.~1999, A&A, 350, L35; Kwok et al.~2001, ApJ, 554, L87). These features show similarity with the infrared spectra of kerogen (Papoular 2001, A&A, 378, 597), which are also found in meteorites.
The origin of the strong emission feature at 21 \mum remains a mystery. Since its initial discovery by the IRAS satellite in 1989 (Kwok et al.~1989, ApJ, 345, L51), now 12 carbon-rich post-AGB stars have been found to show this feature. The broad and smooth nature of this feature suggests that it is due to a solid (Volk et al.~1999, ApJ, 516, L99). Although the 21-\mum feature has been suggested to be due to hydrogenated fullerences or titanium carbide nanoclusters, no firm identification has been made.
This work is supported by the Natural Sciences and Engineering Research Council of Canada, and by a Killam Fellowship from the Canada Council for the Arts.
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The author(s) of this abstract have provided an email address for comments about the abstract: kwok@iras.ucalgary.ca
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.