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arXiv 1808.08201astro-ph.EP
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极端条件下SiC的状态方程:对富碳系外行星内部的新认识

Equation of state of SiC at extreme conditions: new insight into the interior of carbon rich exoplanets

F. Miozzi, G. Morard, D. Antonangeli, A. N. Clark, M. Mezouar, C. Dorn, A. Rozel, G. Fiquet

摘要:

主恒星的成分与围绕其运行的行星的成分之间有着直接的关系。因此,最近发现的具有不寻常化学成分的恒星,特别是富含碳而不是氧的恒星,支持了以碳化物而不是氧化物为主的系外行星的存在。因此,近年来人们对高温高压下的Si-C二元系进行了一些研究。尽管如此,在系外行星内部的PT条件下的碳化物的性质仍然没有得到充分的约束,有效地阻碍了可靠的行星建模。在这里,我们提出了一个原位X射线衍射研究的Si-C二元系统高达200 GPa和3500 K,显着扩大了以前的实验研究探索的压力范围。收集的大量数据使我们能够适当地研究相图,并细化从锌矿床到岩盐结构的过渡线的克拉珀龙斜率。高压相具有低压缩性和低热膨胀的特点,并给出了高压相的压力-体积-温度状态方程。我们的研究结果被用来模拟理想的富C系外行星的最终成员组成。特别是,我们推导出质量半径的关系,并进行了数值模拟,定义流变参数和初始条件,导致在这样的SiC行星对流发病。我们证明,如果限制到富含硅酸盐的地幔成分,质量半径关系的解释可能会低估系外行星的内部多样性。

英文摘要:

There is a direct relation between the composition of a host star and that of the planets orbiting around it. As such, the recent discovery of stars with unusual chemical composition, notably enriched in carbon instead of oxygen, support the existence of exoplanets with a chemistry dominated by carbides instead of oxides. Accordingly several studies have been recently conducted on the Si C binary system at high pressure and temperature. Nonetheless, the properties of carbides at the P T conditions of exoplanets interiors are still inadequately constrained, effectively hampering reliable planetary modeling. Here we present an in situ X ray diffraction study of the Si C binary system up to 200 GPa and 3500 K, significantly enlarging the pressure range explored by previous experimental studies. The large amount of collected data allows us to properly investigate the phase diagram and to refine the Clapeyron slope of the transition line from the zinc blende to the rock salt structure. Furthermore the pressure volume temperature equation of state are provided for the high pressure phase, characterized by low compressibility and thermal expansion. Our results are used to model idealized C rich exoplanets of end members composition. In particular, we derived mass radius relations and performed numerical simulations defining rheological parameters and initial conditions which lead to onset of convection in such SiC planets. We demonstrate that if restrained to silicate rich mantle compositions, the interpretation of mass radius relations may underestimate the interior diversity of exoplanets.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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