对GJ 504基本性能的重新评估：化学成分和年龄
A critical reassessment of the fundamental properties of GJ 504: Chemical composition and age
摘要：
近年来，新的观测技术和理论模型的发展极大地推动了系外行星研究领域的发展。尽管已经取得了重大成就，可以探测到数千个太阳系外系统，但仍然需要全面了解行星的形成和演化机制。一个相关的限制是由行星恒星年龄测量的准确性给出的。恒星GJ 504被发现拥有一个亚恒星伴星，其性质存在强烈争议。由于该系统年龄的不确定性，最近在文献中出现了不同的观点：$\sim$ 1.6亿年的年轻年龄意味着一颗巨行星作为伴星，但最近的一次修订指出太阳年龄（$\sim$ 4 Gyr），而不是棕矮星。为了阐明这一有争议的话题，我们对GJ 504进行了高分辨率光谱研究，以获得恒星参数，金属丰度以及轻元素和重元素的丰度，提供完整的化学表征。主要目的是推断这个系统的进化阶段（因此年龄）的线索。我们对GJ 504相对于两颗参考星进行了严格的差分（逐行）分析，这两颗参考星是行星宿主矮$ι$ Hor和亚巨星HIP 84827。前者在这方面至关重要，因为它的恒星参数（因此演化阶段）受到星震观测的很好约束。无论零点偏移，我们的差分方法使我们能够把严格的限制年龄的GJ 504相对于$ι$霍尔，从而最大限度地减少内部的不确定性。我们发现GJ 504的表面重力比主序星$ι$ Hor低0.2 $\pm$ 0.07 dex，这表明过去的关闭演化[.]
英文摘要：
The recent development of brand new observational techniques and theoretical models have greatly advanced the exoplanet research field. Despite significant achievements, which have allowed the detection of thousands extrasolar systems, a comprehensive understanding of planetary formation and evolution mechanisms is still desired. One relevant limitation is given by the accuracy in the measurements of planet-host star ages. The star GJ 504 has been found to host a substellar companion whose nature is strongly debated. There has been a recent difference of opinion in the literature owing to the uncertainty on the age of the system: a young age of $\sim$ 160 Myr would imply a giant planet as a companion, but a recent revision pointing to a solar age ($\sim$ 4 Gyr) instead suggests a brown dwarf. With the aim of shedding light on this debated topic, we have carried out a high-resolution spectroscopic study of GJ 504 to derive stellar parameters, metallicity, and abundances of both light and heavy elements, providing a full chemical characterisation. The main objective is to infer clues on the evolutionary stage (hence the age) of this system. We performed a strictly differential (line-by-line) analysis of GJ 504 with respect to two reference stars, that is the planet-host dwarf $ι$ Hor and the subgiant HIP 84827. The former is crucial in this context because its stellar parameters (hence the evolutionary stage) is well constrained from asteroseismic observations. Regardless of the zero point offsets, our differential approach allows us to put tight constraints on the age of GJ 504 with respect to $ι$ Hor, thereby minimising the internal uncertainties. We found that the surface gravity of GJ 504 is 0.2 $\pm$ 0.07 dex lower than that of the main-sequence star $ι$ Hor, suggesting a past turn-off evolution[...]
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