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arXiv 2007.10262astro-ph.EPastro-ph.SR
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GJ 357 b：一颗围绕极其不活跃的主星运行的超级地球

GJ 357 b: A Super-Earth Orbiting an Extremely Inactive Host Star

D. Modirrousta-Galian, B. Stelzer, E. Magaudda, J. Maldonado, M. Güdel, J. Sanz-Forcada, B. Edwards, G. Micela

备注：
Accepted for publication in A&A
发表信息：
A&A 641, A113 (2020)
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摘要：

在本文中，我们提出了一个深X射线观测附近的M矮星GJ 357，并用它来限制其行星，GJ 357 b的大气演化。我们还分析了GJ 357恒星参数的系统误差，以了解它们如何影响感知的行星性质。我们通过比较观测到的主星X射线光度来估计GJ 357 b的年龄，这些光度来自最近的{ \em XMM-牛顿}观测{（$\log{L_{\rm x}}\,{\rm [erg/s]} = 25.73$），与M矮星的$L_{\rm x} -$年龄关系。我们发现，GJ 357呈现出有史以来测量到的M矮星的最低X射线活动水平之一，我们对它的年龄设定了一个下限$5$，Gyr。使用这个年龄限制，我们执行一个原始的原始大气水库向后重建。此外，通过考虑恒星参数的系统误差，我们找到了一个可能的行星质量，半径和密度的范围。通过对GJ 357 b辐照历史的后向重建，发现其初始原始大气质量的上限为$\sim \rm 38M_{\oplus}$。一个比这大得多的初始大气层储层可能在X射线和紫外线照射的历史中幸存下来，因此与目前的观测结果不一致。尽管目前不可能存在原始包层，但火山活动和释气可能有助于形成次级大气。在此假设下，我们给出了GJ 357 b的三种不同的合成红外光谱，包括$100\%~\rm CO_{2}$、$100\%~\rm SO_{2}$和$75\%~ \rm N_{2}$、$24\%~\rm CO_{2}$和$1\%~\rm H_{2}O$。

英文摘要：

In this paper we present a deep X-ray observation of the nearby M dwarf GJ 357 and use it to put constraints on the atmospheric evolution of its planet, GJ 357 b. We also analyse the systematic errors in the stellar parameters of GJ 357 in order to see how they affect the perceived planetary properties. We estimate the age of GJ 357 b by comparing the observed X-ray luminosity of its host star, derived from a recent {\em XMM-Newton} observation {($\log{L_{\rm x}}\,{\rm [erg/s]} = 25.73$), with $L_{\rm x} -$ age relations for M dwarfs. We find that GJ 357 presents one of the lowest X-ray activity levels ever measured for an M dwarf, and we put a lower limit on its age of $5$\,Gyr.} Using this age limit, we perform a backwards reconstruction of the original primordial atmospheric reservoir. Furthermore, by considering the systematic errors in the stellar parameters, we find a range of possible planetary masses, radii, and densities. From the backwards reconstruction of GJ 357 b's irradiation history we find that the upper limit of its initial primordial atmospheric mass is $\sim \rm 38M_{\oplus}$. An initial atmospheric reservoir significantly larger than this may have survived through the X-ray and ultraviolet irradiation history, hence being inconsistent with current observations that suggest a telluric composition. In spite of the unlikelihood of a currently existing primordial envelope, volcanism and outgassing may have contributed to a secondary atmosphere. Under this assumption, we present three different synthetic infrared spectra for GJ 357 b that one might expect, consisting of $100\%~\rm CO_{2}$, $100\%~\rm SO_{2}$, and $75\%~ \rm N_{2}$, $24\%~\rm CO_{2}$ and $1\%~\rm H_{2}O$.

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