太阳光球中铪和钍的丰度。来自CO5BOLD 3D流体动力学模型大气的结果
The solar photospheric abundance of hafnium and thorium. Results from CO5BOLD 3D hydrodynamic model atmospheres
摘要：
内容：稳定元素铪（Hf）和放射性元素钍（Th）最近被认为是恒星放射性年代测定的合适配对。这种元素对的适用性需要建立恒星光谱学。目的：利用\cobold三维流体动力学模式大气，对太阳光球中Hf和Th的丰度进行了光谱测定。我们把这纳入一个更广泛的背景下，通过调查的3D丰度校正一组G-和F-型矮星。方法：高分辨率，高信噪比的太阳光谱进行了比较，太阳CO 5 BOLD模型上进行的线合成计算。对于其他大气，我们比较了CO 5 BOLD 3D和相关的1D模型的合成光谱。结果：对于Hf，我们发现光球丰度A（Hf）=0.87+-0.04，与以前的分析，基于一维模型大气。弱Th ii 401.9 nm线构成太阳光谱中唯一可用的Th丰度指示器。它位于镍铁混合物的红翼中，表现出不可忽略的对流不对称性。考虑到与不对称相关的额外吸收，我们得到A（Th）=0.09+-0.03，与陨石丰度一致，比以前的光球丰度测定低约0.1德克斯。结论：据我们所知，只有第二次强调了对流线不对称性对丰度推导的不可忽略的影响。三维流体动力学模拟应采用测量Th丰度的矮星，如果类似的混合存在，在太阳的情况下。相比之下，3D对Hf丰度的影响在G-到中等F-型矮星和次巨星中很小，并且可以方便地使用1D模型大气。
英文摘要：
Context: The stable element hafnium (Hf) and the radioactive element thorium (Th) were recently suggested as a suitable pair for radioactive dating of stars. The applicability of this elemental pair needs to be established for stellar spectroscopy. Aims: We aim at a spectroscopic determination of the abundance of Hf and Th in the solar photosphere based on a \cobold 3D hydrodynamical model atmosphere. We put this into a wider context by investigating 3D abundance corrections for a set of G- and F-type dwarfs. Method: High-resolution, high signal-to-noise solar spectra were compared to line synthesis calculations performed on a solar CO5BOLD model. For the other atmospheres, we compared synthetic spectra of CO5BOLD 3D and associated 1D models. Results: For Hf we find a photospheric abundance A(Hf)=0.87+-0.04, in good agreement with a previous analysis, based on 1D model atmospheres. The weak Th ii 401.9 nm line constitutes the only Th abundance indicator available in the solar spectrum. It lies in the red wing of an Ni-Fe blend exhibiting a non-negligible convective asymmetry. Accounting for the asymmetry-related additional absorption, we obtain A(Th)=0.09+-0.03, consistent with the meteoritic abundance, and about 0.1 dex lower than obtained in previous photospheric abundance determinations. Conclusions: Only for the second time, to our knowledge, has am non-negligible effect of convective line asymmetries on an abundance derivation been highlighted. Three-dimensional hydrodynamical simulations should be employed to measure Th abundances in dwarfs if similar blending is present, as in the solar case. In contrast, 3D effects on Hf abundances are small in G- to mid F-type dwarfs and sub-giants, and 1D model atmospheres can be conveniently used.
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