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 mÅ in equivalent width. This corresponds to a mass-loss rate of less than ∼10⁹ g s⁻¹ 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 nondetection of Lyα absorption by Ehrenreich et al., our helium nondetection 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.

我们通过使用Keck / NIRSPEC进行两次穿越，获取1083 nm线的高分辨率光谱，从热的超地球55 Cnc e中逸出氦气。我们无法检测到氦气的吸收量低至过量吸收量250 ppm或等效宽度0.27mÅ的90％上限。这对应于小于〜10 ⁹ gs ^-1的质量损失率假设帕克风模型的大气圈温度为5000–6000 K，尽管精确的约束在很大程度上取决于模型假设。我们同时考虑了氢和氦为主的大气成分，并且在两种情况下都发现了质量损失率的相似界限。我们的流体力学模型表明，如果在55 Cnc e上存在轻质大气，我们的观察将很容易检测到它。加上Ly的回避侦测α吸收埃伦赖希等，我们的氦回避侦测显示，55数控Ë或者从未增生一种原始的气息在首位或气体盘消散后不久失去了其原始的氛围。