Laboratory measurement of optical constants of solid SiO and application to circumstellar dust
Laboratory measurement of optical constants of solid SiO and application to circumstellar dust
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固体SiO光学常数的实验室测量及其在星周尘埃中的应用
DOI：
10.1051/0004-6361/201220803
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发表时间：
2012
影响因子：
6.5
通讯作者：
M. Trieloff
中科院分区：
文献类型：
--
作者：
S. Wetzel;M. Klevenz;H. Gail;A. Pucci;M. Trieloff
上下文。硅酸盐矿物属于在宇宙环境中形成的最丰富的固体。它们的形成需要每个硅原子有足够数量的氧原子。对于标准的宇宙元素混合物来说，这通常是理所当然的，但在从m星的富氧化学过渡到c星的富碳化学时，这就成了一个问题。在中间型s星中，大部分氧和碳被CO和SiO分子的形成所消耗，剩余的氧在固体中形成sio4 -四面体变得稀缺。在这种条件下，来自气相的SiO分子可能凝结成固体SiO。固体SiO的红外吸收光谱与普通硅酸盐不同，在18µm左右不存在Si-O- si弯曲模式，而在10µm左右存在Si-O键拉伸模式的吸收带。最近有报道（Hony et al. 2009），在许多s星光谱中观察到这种特殊的r特征。目标。我们证明，这一观察结果可以解释为固体SiO的形成，作为主要的尘埃成分，在C/O丰度比接近于1。方法。通过在Si（111）晶圆上气相沉积制备的SiO薄膜的透射率测量，确定了固体SiO的红外吸收特性。利用Brendel-oscillator模型，从测量光谱中推导出SiO的介电函数，该模型特别适合于非晶材料光学性质的表征。将所得结果应用于含固体SiO粉尘的环形粉尘壳辐射传输模型计算，以确定SiO粉尘引起的光谱特征。结果。合成光谱与观测光谱的比较表明，固体氧化硅发射带的主要光谱特征与某些s星观测到的以10µm为中心但不伴有18µm波段的发射带基本一致。我们提出固体SiO是这种10µm光谱特征的载流子材料。
Context. Silicate minerals belong to the most abundant solids that form in cosmic environments. Their formation requires that a suffi cient number of oxygen atoms per silicon atom is freely available. For the standard cosmic element mixture this can usually be taken for granted, but this becomes a problem at the transition from the oxygen rich chemistry of M-stars to the carbon rich chemistry of C-stars. In the intermediate type S-stars most of the oxygen and carbon is consumed by formation of CO and SiO molecules, and left-over oxygen to build SiO4-tetrahedrons in solids becomes scarce. Under such conditions SiO molecules from the gas phase may condense into solid SiO. The infrared absorption spectrum of solid SiO differs from that of normal silicates by the absence of Si-O-Si bending modes around 18µm while the absorption band due to Si-O bond stretching modes at about 10µm is present. Recently it has been reported (Hony et al. 2009) that exactly this particula r characteristics is observed in a number of S-star spectra. Aims. We demonstrate that this observation may be explained by the formation of solid SiO as a major dust component at C/O abundance ratios close to unity. Methods. The infrared absorption properties of solid SiO are determined by laboratory transmission measurements of thin films of SiO produced by vapour deposition on a Si(111) wafer. From the measured spectra the dielectric function of SiO is derived by using a Brendel-oscillator model, particularly suited for the rep resentation of optical properties of amorphous materials. The results are used in model calculations of radiative transfer in circumstell ar dust shells with solid SiO dust in order to determine the spectral features due to SiO dust. Results. Comparison of synthetic and observed spectra shows that reasonable agreement is obtained between the main spectral characteristics of emission bands due to solid silicon monoxide and an emission band centred on 10µm, but without accompanying 18µm band, observed in some S-stars. We propose that solid SiO is the carrier material of this 10µm spectral feature.