论文标题
Europium作为LODESTAR：陆地系外运动中放射热产生的诊断
Europium as a lodestar: diagnosis of radiogenic heat production in terrestrial exoplanets
论文作者
论文摘要
长期寿命的放射性核素，例如$^{40} $ k，$^{232} $ th，$^{235} $ u和$^{238} $ u，在地面型星球的地幔中持续热量产生。作为难治性元素，陆地系外行星中Th和U的浓度被隐式地反映在恒星宿主的光球丰度中。但是，由于相关光谱特征的普遍缺乏和弱点，在实践中很难确定这些恒星丰度。我们提请人们注意耐火材料，$ r- $过程元素europium，这可以用作方便且实用的代理，用于在系外行星系统中进行放射性加热的种群分析。作为一个案例研究，我们介绍了$α$ CEN A和B的欧盟的丰度的确定，我们发现Europium耗尽了$ \ sim $ 0.1 dex和$ \ sim $ \ sim $ 0.15 $ 0.15 DEX与两个binary组件相比，$ \ sim $ 0.15。首先，可以将测量的欧盟丰度转换为$^{232} $ th，$^{235} $ u和$^{238} $ u具有观察性约束，而$^{40} $ k的丰富度与银河化学化学进化模型独立近似。 We find that the radiogenic heat budget in an $α$-Cen-Earth is $73.4^{+8.3}_{-6.9}$ TW upon its formation and $8.8^{+1.7}_{-1.3}$ TW at the present day, respectively $23\pm5$ % and $54\pm5$ % lower than that in the Hadean and modern Earth.结果，预计$α$ cen-Erth中的地幔对流总体比地球弱（假设其他条件是相同的），因此，这样的行星在地质上会较少，从而抑制其长期恢复其外壳和挥发物的长期潜力。由于欧盟的丰度可用于大量类似阳光的恒星，因此提出的方法可以扩展我们对其他岩石世界的性质进行预测的能力。
Long-lived radioactive nuclides, such as $^{40}$K, $^{232}$Th, $^{235}$U and $^{238}$U, contribute to persistent heat production in the mantle of terrestrial-type planets. As refractory elements, the concentrations of Th and U in a terrestrial exoplanet are implicitly reflected in the photospheric abundances in the stellar host. However, a robust determination of these stellar abundances is difficult in practice owing to the general paucity and weakness of the relevant spectral features. We draw attention to the refractory, $r-$process element europium, which may be used as a convenient and practical proxy for the population analysis of radiogenic heating in exoplanetary systems. As a case study, we present a determination of Eu abundances in the photospheres of $α$ Cen A and B. We find that europium is depleted with respect to iron by $\sim$ 0.1 dex and to silicon by $\sim$ 0.15 dex compared to solar in both binary components. To first order, the measured Eu abundances can be converted to the abundances of $^{232}$Th, $^{235}$U and $^{238}$U with observational constraints while the abundance of $^{40}$K is approximated independently with a Galactic chemical evolution model. We find that the radiogenic heat budget in an $α$-Cen-Earth is $73.4^{+8.3}_{-6.9}$ TW upon its formation and $8.8^{+1.7}_{-1.3}$ TW at the present day, respectively $23\pm5$ % and $54\pm5$ % lower than that in the Hadean and modern Earth. As a consequence, mantle convection in an $α$-Cen-Earth is expected to be overall weaker than that of the Earth (assuming other conditions are the same) and thus such a planet would be less geologically active, suppressing its long-term potential to recycle its crust and volatiles. With Eu abundances being available for a large sample of Sun-like stars, the proposed approach can extend our ability to make predictions about the nature of other rocky worlds.
