论文标题
迷你北极k2-18 b的高能环境和大气逃逸
The high-energy environment and atmospheric escape of the mini-Neptune K2-18 b
论文作者
论文摘要
K2-18 B是一种过渡的迷你新闻，它在附近的（38 pc）凉爽的M3矮人旋转，位于其温带照射区域内。我们报告使用安装在哈勃太空望远镜（HST）上的空间望远镜成像光谱仪（STIS）仪器（HST）的空间望远镜成像光谱仪（STIS）仪器使用Lyman-$α$ Transit光谱搜索氢从大气中逃脱。我们分析了恒星Lyman-$α$在其蓝色和红移的翅膀中的发射的时间序列。我们发现，在行星过境期间，与前透射发射相比，在行星过境期间，K2-18的平均蓝光发射降低了$ 67 \％\ pm 18 \％$，暂时表明H原子的存在急剧逃脱并被辐射压力吹走。这种解释不是确定的，因为它依赖于一个部分过境。基于重建的Lyman- $α$的K2-18排放，我们估计EUV辐照$ 10^1-10^2 $ ERG S $^{ - 1} $ CM $ $^{ - 2} $和总逃生率，订单为$ 10^8 $ g s $^$ g s $^{ - 1} $。推断的逃逸率表明，地球只会损失其质量的一小部分（<1％），并在其寿命中保留挥发性丰富的气氛。需要更多的观察结果来排除出色的可变性效应，确认透视吸收并更好地评估K2-18 b的大气逃逸和高能环境。
K2-18 b is a transiting mini-Neptune that orbits a nearby (38 pc) cool M3 dwarf and is located inside its region of temperate irradiation. We report on the search for hydrogen escape from the atmosphere K2-18 b using Lyman-$α$ transit spectroscopy with the Space Telescope Imaging Spectrograph (STIS) instrument installed on the Hubble Space Telescope (HST). We analyzed the time-series of the fluxes of the stellar Lyman-$α$ emission of K2-18 in both its blue- and redshifted wings. We found that the average blueshifted emission of K2-18 decreases by $67\% \pm 18\%$ during the transit of the planet compared to the pre-transit emission, tentatively indicating the presence of H atoms escaping vigorously and being blown away by radiation pressure. This interpretation is not definitive because it relies on one partial transit. Based on the reconstructed Lyman-$α$ emission of K2-18, we estimate an EUV irradiation between $10^1-10^2$ erg s$^{-1}$ cm$^{-2}$ and a total escape rate in the order of $10^8$ g s$^{-1}$. The inferred escape rate suggests that the planet will lose only a small fraction (< 1%) of its mass and retain its volatile-rich atmosphere during its lifetime. More observations are needed to rule out stellar variability effects, confirm the in-transit absorption and better assess the atmospheric escape and high-energy environment of K2-18 b.
