论文标题
没有55 CNC E的逃避氦气
No escaping helium from 55 Cnc e
论文作者
论文摘要
我们使用KECK/NIRSPEC在两次过渡过程中捕获了1083 nm线的高分辨率光谱，从而从热地超过55 CNC E中搜索逃避氦气。我们检测到氦气吸收降至90 \％的上限为250 ppm的多余吸收或等效宽度为0.27毫秒。这对应于质量损失率小于$ \ sim10^9 $ g/s，假设Parker风模型具有合理的外流温度为5000-6000 K，尽管精确的约束很大程度上取决于模型假设。我们考虑氢和氦气的大气组成，并在两种情况下都在质量损失率上找到相似的界限。我们的流体动力学模型表明，如果在55 CNC E上存在轻巧的气氛，我们的观察结果将很容易检测到。加上Ehrenreich等人2012年Lyman $α$吸收的未检测，我们的氦气非检测表明，首先，55 CNC E要么从未产生原始气氛，要么在散发煤气盘耗散后不久就失去了原始气氛。
We search for escaping helium from the hot super Earth 55 Cnc e by taking high-resolution spectra of the 1083 nm line during two transits using Keck/NIRSPEC. We detect no helium absorption down to a 90\% upper limit of 250 ppm in excess absorption or 0.27 milli-Angstrom in equivalent width. This corresponds to a mass loss rate of less than $\sim10^9$ g/s assuming a Parker wind model with a plausible exosphere temperature of 5000-6000 K, although the precise constraint is heavily dependent on model assumptions. We consider both hydrogen- and helium-dominated atmospheric compositions, and find similar bounds on the mass loss rate in both scenarios. Our hydrodynamical models indicate that if a lightweight atmosphere exists on 55 Cnc e, our observations would have easily detected it. Together with the non-detection of Lyman $α$ absorption by Ehrenreich et al 2012, our helium non-detection indicates that 55 Cnc e either never accreted a primordial atmosphere in the first place, or lost its primordial atmosphere shortly after the dissipation of the gas disk.
