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dc.contributor.authorSpeck, Angela K.eng
dc.contributor.authorThompson, Grant D.eng
dc.contributor.authorHofmeister, Anne M.eng
dc.date.issued2005eng
dc.descriptiondoi: 10.1086/496955eng
dc.description.abstractStars on the asymptotic giant branch (AGB) produce dust in their circumstellar shells. The nature of the dust-forming environment is influenced by the evolution of the stars, in terms of both chemistry and density, leading to an evolution in the nature of the dust that is produced. Carbon-rich AGB stars are known to produce silicon carbide (SiC). Furthermore, observations of the ~11 μm SiC feature show that the spectral features change in a sequence that correlates with stellar evolution. We present new infrared spectra of amorphous SiC and show that the ~9 μm feature seen in both emission and absorption, and correlated with trends in the ~11 μm feature, may be due to either amorphous SiC or nanocrystalline diamond with a high proportion of Si substituting for C. Furthermore, we identify SiC absorption in three ISO spectra of extreme carbon stars, in addition to the four presented by Speck and coworkers. An accurate description of the sequence in the IR spectra of carbon stars requires accounting for both SiC emission and absorption features. This level of detail is needed to infer the role of dust in the evolution of carbon stars. Previous attempts to find a sequence in the infrared spectra of carbon stars considered SiC emission features while neglecting SiC absorption features, leading to an interpretation of the sequence that inadequately describes the role of dust. We show that the evolutionary sequence in carbon star spectra is consistent with a grain size evolution such that dust grains get progressively smaller as the star evolves. The evolution of the grain sizes provides a natural explanation for the shift of the ~11 μm SiC feature in emission and in absorption. Further evidence for this scenario is seen in both post-AGB star spectra and in meteoritic studies of presolar grains.eng
dc.description.sponsorshipSupport for A. M. H. was provided by NASA grant APRA04-0000-0041.eng
dc.identifier.citationAngela K. Speck et al. 2005 ApJ 634 426eng
dc.identifier.issn0004-637Xeng
dc.identifier.urihttp://hdl.handle.net/10355/9928eng
dc.languageEnglisheng
dc.publisherAmerican Astronomical Societyeng
dc.relation.ispartofcollectionUniversity of Missouri--Columbia. College of Arts and Sciences. Department of Physics and Astronomy. Physics and Astronomy publicationseng
dc.subjectinfrared starseng
dc.subject.lcshCircumstellar mattereng
dc.subject.lcshCarbon starseng
dc.titleThe Effect of Stellar Evolution on SiC Dust Grain Sizeseng
dc.typeArticleeng


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