Near-infrared absorption properties of oxygen-rich stardust analogs The influence of coloring metal ions
Near-infrared absorption properties of oxygen-rich stardust analogs The influence of coloring metal ions
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DOI：
10.1051/0004-6361/201015219
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发表时间：
2011-02-01
影响因子：
6.5
通讯作者：
Wehrhan, O.
中科院分区：
文献类型：
--
作者：
Zeidler, S.;Posch, T.;Wehrhan, O.
上下文。几种与天体物理学相关的固体氧化物和硅酸盐在纯形式下在可见光和近红外波段具有极小的不透明度。在这些波长范围内，很难获得不透明度及其复折射率虚部k的数据集。我们的目的是测定尖晶石，金红石，锐钛矿和橄榄石的k，特别是在近红外区域。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：制备天然矿物的小截面和电弧炉下的熔体液滴合成。在这两种情况下，样品的吸收特性通过透射光谱测量。尖晶石（MgAl2O4）、锐钛矿、金红石（均为TiO2）和橄榄石(（Mg,Fe)(2)SiO4）的光学常数已扩展到可见光和近红外光谱。我们强调，k（lambda）和吸收截面Q(abs)（lambda）的单个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）在包括星尘颗粒在内的天然矿物中是非常罕见的，如果它们存在的话。k和Q(abs)（lambda）的数据对于星尘颗粒的各种物理性质（如温度和辐射压力）非常重要。随着杂质含量Q(abs)（λ）的增加，星周壳内小颗粒的平衡温度也随之升高。我们将讨论为什么会出现这种情况，以及在何种程度上出现这种情况。
Context. 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.Aims. 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.Methods. 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.Results. For spinel (MgAl2O4), anatase, rutile (both TiO2), and olivine ((Mg,Fe)(2)SiO4), the optical constants have been extended to the visual and near-infrared. We highlight that the individual values of k(lambda) and the absorption cross section Q(abs)(lambda) 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.Conclusions. Data for k and Q(abs)(lambda) are important for various physical properties of stardust grains such as temperature and radiation pressure. With increasing Q(abs)(lambda) 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.