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  Structural Investigation of Silicon Carbide X Grains: Constraints on Condensation in Supernova Ejecta

Kodolányi, J., Vollmer, C., Hoppe, P., & Mueller, M. (2018). Structural Investigation of Silicon Carbide X Grains: Constraints on Condensation in Supernova Ejecta. Astrophysical Journal, 868(1): 34. doi:10.3847/1538-4357/aae482.

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Kodolányi, János1, Author           
Vollmer, Christian2, Author
Hoppe, Peter1, Author           
Mueller, Maren2, Author
Affiliations:
1Particle Chemistry, Max Planck Institute for Chemistry, Max Planck Society, ou_1826291              
2external, ou_persistent22              

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 Abstract: We analyzed seven presolar SiC grains of supernova origin (average diameter: 1–2 μm) with transmission electron microscopy. Five grains are polycrystalline, whereas two grains are single crystals. Individual crystal domains of polycrystalline grains are in epitaxial relationship, with two grains consisting almost entirely of twinned crystal domains. Most grains are free of inclusions (only one TiC inclusion and one iron- and nickel-rich inclusion were found in two separate grains). Almost all crystals have cubic symmetry (3C polytype), but we found hexagonal SiC (6H polytype) in two grains. The large range of crystal domain sizes (average diameter: 50–970 nm), as well as the larger fraction of noncubic SiC polytypes in supernova grains relative to SiC grains that crystallized in the winds of asymptotic giant branch (AGB) stars, suggest that SiC condensation in supernova ejecta occurs at a larger range of chemical and physical conditions, including supersaturation, than in the winds of AGB stars. Modeling condensation of SiC struggles to produce SiC grains as large as, or bigger than, observed here, if condensation of large (i.e., several μm in diameter) graphite grains is to precede that of SiC, which is suggested by the presolar grain record and published equilibrium condensation models. We propose that future models of graphite and SiC condensation in SN ejecta explore higher ejecta densities than before, as well as gas compositions that are more silicon- and carbon-rich. Furthermore, we infer that some supernova SiC grains may have formed without prior condensation of graphite from their parent gas.

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Language(s): eng - English
 Dates: 2018
 Publication Status: Published online
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 Rev. Type: -
 Identifiers: ISI: 000450221800034
DOI: 10.3847/1538-4357/aae482
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Title: Astrophysical Journal
Source Genre: Journal
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Publ. Info: Chicago, IL : University of Chicago Press for the American Astronomical Society
Pages: - Volume / Issue: 868 (1) Sequence Number: 34 Start / End Page: - Identifier: ISSN: 0004-637X
CoNE: https://pure.mpg.de/cone/journals/resource/954922828215_2