Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...278..226g&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 278, no. 1, p. 226-230
Astronomy and Astrophysics
Astrophysics
31
Emission Spectra, Planetary Nebulae, Shell Stars, Stellar Envelopes, Molecular Spectra, Stellar Composition, Stellar Temperature
Scientific paper
Solid state SiS2 is proposed as the material responsible for the recently discovered 21 micrometer emission feature that is observed in the carbon-rich circumstellar shells of certain protoplanetary nebulae. Sulfurized SiC, or SiS2 mantles on grains of either SiC or a:C-H are discussed as possible forms for which no spectroscopic laboratory observations yet exist. The identification with a relatively minor species and required special abundance ratios are consistent with the low incidence rate that the 21 micrometer feature presents in the population of carbon rich objects. It is also consistent with the lack of a good correlation between the 21 micrometer feature and the other solid-state spectroscopic features that have been observed in protoplanetaries that would be expected if the feature arose from molecules composed of H, C, N, and O. SiS2 condensate is consistent with the circumstellar shell temperature range, TCS approximately equal to or less than 150 K, at which the feature appears, and the available mass of SiS2, MSiS2 approx. = 5 x 10-6 solar mass, that is possible in the circumstellar shell.
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