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Tham khảo sách 'silicon carbide - materials, processing and applications in electronic devices_2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 11 Optical Properties and Applications of Silicon Carbide in Astrophysics Karly M. Pitman1 Angela K. Speck2 Anne M. Hofmeister3 and Adrian B. Corman3 1Planetary Science Institute 2Dept. of Physics Astronomy University of Missouri-Columbia 3Dept. of Earth Planetary Sciences Washington University in St. Louis USA 1. Introduction Optical properties namely spectra and optical functions of silicon carbide SiC have been of great interest to astrophysicists since SiC was first theoretically posited to exist as dust i.e. submicron-sized solid state particles in carbon-rich circumstellar regions Gilman 1969 Friedemann 1969 . The prediction that SiC in space should re-emit absorbed radiation as a spectral feature in the X 10-13 pm wavelength region Gilra 1971 1972 was confirmed by a broad emission feature at X 11.4 pm in the spectra of several carbon-rich stars Hackwell 1972 Treffers Cohen 1974 . Many carbon-rich evolved stars exhibit the X 11 pm feature in emission and SiC is now believed to be a significant constituent around them Speck 1998 Speck et al. 2009 and references therein . 1.1 Role of SiC in stellar environments Detection of SiC in space provides much information on circumstellar environments because the chemical composition and structure of dust in space is correlated with e.g. the pressure temperature and ratios of available elements in gas around stars. The mere presence of SiC implies that the carbon-to-oxygen C O must be high. Different polytypes of SiC identify the temperature and gas pressure within the dust forming region around a star. The significance of SiC in stars is tied intimately to stellar evolution as dust grains participate in feedback relationships between stars and their circumstellar envelopes that affect mass-loss rates i.e. stellar lifetimes. Meteoritic SiC grains exhibit signatures of s-process enrichment one of the main attributes of the evolutionary track of carbon-rich stars. 1.1.1 S-process isotopic signatures in SiC Elements more .
