Optical constants of refractory oxides at high temperatures Mid-infrared properties of corundum, spinel, and α-quartz, potential carriers of the 13 μm feature
Optical constants of refractory oxides at high temperatures Mid-infrared properties of corundum, spinel, and α-quartz, potential carriers of the 13 μm feature
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DOI：
10.1051/0004-6361/201220459
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发表时间：
2013-05-01
影响因子：
6.5
通讯作者：
Mutschke, H.
中科院分区：
文献类型：
--
作者：
Zeidler, S.;Posch, Th.;Mutschke, H.
上下文许多宇宙尘埃物种，其中包括难熔氧化物，在高于300 K的温度下形成。然而，大多数天体物理学研究都是基于固体的室温光学常数，如尖晶石和尖晶石。这些材料需要一种更真实的方法，特别是在建模晚型恒星的背景下。我们的目的是推导出一套光学常数的选择，天体物理学相关的氧化物尘埃物种具有高熔点。采用高温高压池和傅里叶变换光谱仪测量抛光样品的反射光谱。对于Al 2 O3、MgAl 2 O 4和SiO2晶体，测量了从300 K到900 K以上的光学常数随温度的变化。小粒子光谱也计算从这些数据。所有三个检查氧化物显示出显着的温度依赖性，其中红外波段。对于的情况下，我们发现，13 μ m的发射功能-看到许多AGB星的红外光谱-可以很好地分配给这种矿物物种。在550 K左右的（平均）温度下，用扁长的晶粒实现了该特征的最佳拟合。尖晶石仍然是一个可行的载体的13 μ m的功能，以及，但只有T < 300 K和近球形晶粒形状。在这种情况下，尖晶石颗粒也可以解释31.8 μ m的谱带，该谱带在13 μ m特征的源中经常看到，并且尚未被确定。
Context. Many cosmic dust species, among them refractory oxides, form at temperatures higher than 300 K. Nevertheless, most astrophysical studies are based on the room-temperature optical constants of solids, such as corundum and spinel. A more realistic approach is needed for these materials, especially in the context of modeling late-type stars.Aims. We aimed at deriving sets of optical constants of selected, astrophysically relevant oxide dust species with high melting points.Methods. A high-temperature, high-pressure cell and a Fourier-transform spectrometer were used to measure reflectance spectra of polished samples. For corundum (alpha-Al2O3), spinel (MgAl2O4), and alpha-quartz (SiO2), temperature-dependent optical constants were measured from 300 K up to more than 900 K. Small particle spectra were also calculated from these data.Results. All three examined oxides show a significant temperature dependence of their mid-IR bands. For the case of corundum, we find that the 13 mu m emission feature - seen in the IR spectra of many AGB stars - can very well be assigned to this mineral species. The best fit of the feature is achieved with oblate corundum grains at (mean) temperatures around 550 K. Spinel remains a viable carrier of the 13 mu m feature as well, but only for T < 300 K and nearly spherical grain shapes. Under such circumstances, spinel grains may also account for the 31.8 mu m band that is frequently seen in sources of the 13 mu m feature and which has not yet been identified with certainty.