富氧星尘类似物的近红外吸收特性：着色金属离子的影响
Near-infrared absorption properties of oxygen-rich stardust analogues: The influence of coloring metal ions
摘要：
几种与天体物理学有关的固体氧化物和硅酸盐在其纯净形式下在可见光和近红外线中具有极小的不透明度。在这些波长范围内，不透明度和复折射率虚部k的数据集几乎不可用。我们的目的是确定尖晶石，金红石，金红石，橄榄石，特别是在近红外区域的k。我们的测量是用含杂质的、天然的和合成的星尘类似物进行的。采用了两种实验方法：制备天然矿物的小段和在电弧炉下合成熔滴。在这两种情况下，通过透射光谱测量样品的吸附性能。对于尖晶石（MgAl_2O_4）、金红石（TiO_2）和橄榄石（（Mg，Fe）_2SiO_4），光学常数已扩展到可见光和近红外。我们强调，k和吸收截面的个别值强烈依赖于过渡金属如铁的含量。根据我们的测量，我们推断，k值低于10 ^（-5）的情况在包括星尘颗粒在内的天然矿物中是非常罕见的，如果有的话。k和吸收截面的数据对于星尘颗粒的各种物理性质，如温度和辐射压，都是很重要的。随着杂质吸收截面的增加，星周壳层中小颗粒的平衡温度也随之升高。我们讨论为什么以及在多大程度上是这样。
英文摘要：
Several astrophysically relevant solid oxides and silicates have extremely small opacities in the visual and near-infrared in their pure forms. Datasets for the opacities and for the imaginary part k of their complex indices of refraction are hardly available in these wavelength ranges. We aimed at determining k for spinel, rutile, anatase, and olivine, especially in the near-infrared region. Our measurements were made with impurity-containing, natural, and synthetic stardust analogs. Two experimental methods were used: preparing small sections of natural minerals and synthesizing melt droplets under the electric arc furnace. In both cases, the aborption properties of the samples were measured by transmission spectroscopy. For spinel (MgAl2O4), anatase, rutile (both TiO2), and olivine ((Mg,Fe)2SiO4), the optical constants have been extended to the visual and near-infrared. We highlight that the individual values of k and the absorption cross section depend strongly on the content in transition metals like iron. Based on our measurements, we infer that k values below 10^(-5) are very rare in natural minerals including stardust grains, if they occur at all. Data for k and the absorption cross section are important for various physical properties of stardust grains such as temperature and radiation pressure. With increasing absorption cross section due to impurities, the equilibrium temperature of small grains in circumstellar shells increases as well. We discuss why and to what extent this is the case.
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