标题： 詹姆斯韦伯空间望远镜（JWST）对超级地球GJ 357b的近红外成像光谱仪（NIRISS）透射光谱：一个有利于大气保留的有利目标 显示英文标题

标题： JWST NIRISS Transmission Spectroscopy of the Super-Earth GJ 357b, a Favourable Target for Atmospheric Retention

摘要： 我们展示了詹姆斯韦伯太空望远镜（JWST）NIRISS/SOSS对该超级地球GJ 357 b的传输光谱：这是对该系外行星的首次大气观测。 尽管由于使用过时的星历表错过了前 $\sim$40% 的凌星，但我们仍然恢复了一个没有显示任何明确大气特征的传输光谱。 我们在数据中寻找高斯形状的吸收特征，但发现这种分析得到的结果与一条水平线拟合观察到的现象相当。 我们将传输光谱与一组大气模型网格进行比较，并以 3-$\sigma$置信度拒绝了金属丰度 $\lesssim$高于100$\times$太阳金属丰度（$\sim$4 g/mol）且云层延伸至0.01巴的压力范围内的大气。 我们分析了为什么GJ 357 b上可能存在次生大气，这可能与其较高的逃逸速度以及相对于其他M2.5V恒星而言其宿主恒星的异常不活跃有关。 该恒星的XUV亮度在足够早的时间内下降到快速大气逃逸阈值以下，使得几巴的CO$_2$大气的火山复兴成为可能，尽管存在相当大的不确定性。 最后，我们模拟了使用MIRI/LRS、MIRI测光和NIRSpec/G395H探测GJ 357 b上大气的可能性。 我们发现，通过两次掩食，可以检测到指示存在大气或表面的特征。 此外，通过3到4次凌星，可以检测到含有1000 ppm CO$_2$的1巴氮气丰富的大气。 显示英文摘要

摘要： We present a JWST NIRISS/SOSS transmission spectrum of the super-Earth GJ 357 b: the first atmospheric observation of this exoplanet. Despite missing the first $\sim$40 % of the transit due to using an out-of-date ephemeris, we still recover a transmission spectrum that does not display any clear signs of atmospheric features. We perform a search for Gaussian-shaped absorption features within the data but find that this analysis yields comparable fits to the observations as a flat line. We compare the transmission spectrum to a grid of atmosphere models and reject, to 3-$\sigma$ confidence, atmospheres with metallicities $\lesssim$100$\times$ solar ($\sim$4 g/mol) with clouds at pressures down to 0.01 bar. We analyse how the retention of a secondary atmosphere on GJ 357 b may be possible due to its higher escape velocity compared to an Earth-sized planet and the exceptional inactivity of its host star relative to other M2.5V stars. The star's XUV luminosity decays below the threshold for rapid atmospheric escape early enough that the volcanic revival of an atmosphere of several bars of CO$_2$ is plausible, though subject to considerable uncertainty. Finally, we model the feasibility of detecting an atmosphere on GJ 357 b with MIRI/LRS, MIRI photometry, and NIRSpec/G395H. We find that, with two eclipses, it would be possible to detect features indicative of an atmosphere or surface. Further to this, with 3-4 transits, it would be possible to detect a 1 bar nitrogen-rich atmosphere with 1000 ppm of CO$_2$.