Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002sci...296.1852d&link_type=abstract
Science, Volume 296, Issue 5574, pp. 1852-1855 (2002).
Astronomy and Astrophysics
Astronomy
21
Scientific paper
The inferred crystallographic class of circumstellar silicon carbide based on astronomical infrared spectra is controversial. We have directly determined the polytype distribution of circumstellar SiC from transmission electron microscopy of presolar silicon carbide from the Murchison carbonaceous meteorite. Only two polytypes (of a possible several hundred) were observed: cubic 3C and hexagonal 2H silicon carbide and their intergrowths. We conclude that this structural simplicity is a direct consequence of the low pressures in circumstellar outflows and the corresponding low silicon carbide condensation temperatures.
Amari Sachiko
Bernatowicz Thomas J.
Daulton Tyrone L.
Lewis Reed S.
Messenger Scott
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Astronomers have been debating the nature (structure) of SiC in the outflows of red giants and supernova for years. This question is important because laboratory studies have shown that different SiC structures form under different temperatures and pressures. However, interpretation of the adsorption spectra from stars in regard to the structure of SiC in their outflows is highly debated. To answer the question of what structure the SiC has, the best method is to look directly at the SiC in a microscope. This is what was done in this paper.
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