碳化硅在天体物理学中的光学性质I。新的实验室红外反射光谱和光学常数
Optical properties of silicon carbide for astrophysical applications I. New laboratory infrared reflectance spectra and optical constants
摘要：
碳化硅（SiC）光学常数是天体物理尘埃环境辐射转移模型的基本输入。然而，以前公布的值包含错误，并不能充分代表通常在碳星周围发现的立方（β）SiC多型体的物理性质。我们提供了新的，不妥协的光学常数β-和α-SiC来自单晶反射光谱和定量研究是否有任何差异α-和β-SiC，可以看到在红外光谱和光学功能。以前的SiC光学常数并不能反映真实的体相性质，并且它们仅对窄的晶粒尺寸范围有效。这里提出的新的光学常数将允许狭窄的约束，以放置在天体物理环境中占主导地位的晶粒尺寸和形状分布。此外，我们计算的吸收系数远高于实验室测量，这对使用以前的数据来限制这些尘埃颗粒的丰度产生了影响。
英文摘要：
Silicon Carbide (SiC) optical constants are fundamental inputs for radiative transfer models of astrophysical dust environments. However, previously published values contain errors and do not adequately represent the bulk physical properties of the cubic (beta) SiC polytype usually found around carbon stars. We provide new, uncompromised optical constants for beta- and alpha-SiC derived from single-crystal reflectance spectra and investigate quantitatively whether there is any difference between alpha- and beta-SiC that can be seen in infrared spectra and optical functions. Previous optical constants for SiC do not reflect the true bulk properties, and they are only valid for a narrow grain size range. The new optical constants presented here will allow narrow constraints to be placed on the grain size and shape distribution that dominate in astrophysical environments. In addition, our calculated absorption coefficients are much higher than laboratory measurements, which has an impact on the use of previous data to constrain abundances of these dust grains.
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