Are crystalline silicates and amorphous silicates spatially separated in protoplanetary disks ?
首发时间:2017-05-16
Abstract:Crystalline silicates have been found in comets, in protoplanetary disks around young pre-main sequence stars, in debris disks around main-sequence stars, and in dust shells around evolved stars. Their infrared (IR) emission spectra indicate that they are predominantly magnesium (Mg)-rich and iron (Fe)-poor or even Fe-free. The Stardust cometary samples of crystalline silicate minerals are also predominantly Fe-poor. The Fe content of crystalline silicates not only affects the peak wavelength, width and strength of their vibrational features in the IR, but also affects their ultraviolet (UV) and visual absorptivities. Taking the young Herbig Ae star HD 142527 as a test case, we quantitatively demonstrate that, as a consequence of the latter effect, the crystallinity degree of silicate dust might have been substantially underestimated in various astrophysical regions, and the non-detection of the crystalline silicate emission features does not necessarily imply the absence of crystalline silicate dust; instead, crystalline silicates could be present but are just not heated sufficiently to emit at their characteristic IR vibrational bands.
keywords: Astrophysics Interstellar medium Interstellar dust Circumstellar matter
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原行星尘埃盘结晶硅酸盐和非结晶硅酸盐的空间分布
摘要:结晶硅酸盐已经在彗星、主序前恒星的原行星盘、主序星的碎片盘和演化晚期恒星的星周尘埃包层中探测到。 尘埃的红外发射光谱表明结晶硅酸盐是富Mg贫Fe或者不含Fe。"星尘号"宇宙飞船带回的彗星尘埃样本也揭示了结晶硅酸盐尘粒是贫Fe。结晶硅酸盐化学组分中的Fe含量不仅影响了红外波段光谱的峰值波长、谱线宽度和强度,而且也影响了其紫外波段的吸收。以Herbig Ae HD 142527为例,本文通过定量计算揭示不同含Fe量的硅酸盐在紫外和光学波段吸收率差异将导致对硅酸盐结晶度的低估。天文观测中未观测到结晶硅酸盐的尖锐谱线不能证明该天体物理环境不存在结晶硅酸盐,结晶硅酸盐由于在紫外较弱的吸收能力导致无法在红外波段显现发射特征谱。
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No.4732592119564714****
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原行星尘埃盘结晶硅酸盐和非结晶硅酸盐的空间分布
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