干旱或多云：使用高分辨率光谱学表征超级地球55 Cancri e的大气
Arid or Cloudy: Characterizing the Atmosphere of the super-Earth 55 Cancri e using High-Resolution Spectroscopy
摘要：
附近的超级地球55 Cnc e围绕着一颗明亮的（V = 5.95等）恒星运行，周期约为18小时，质量约为8个地球质量。它的大气层可能富含水，并且有很大的高度，尽管试图描述它的特征已经产生了模糊的结果。在这里，我们提出了一个敏感的搜索水和TiO在其大气中的高光谱分辨率使用双子座北望远镜和GRACES摄谱仪。我们将观测结果与斯巴鲁和CFHT先前的观测结果相结合，改进了对水蒸气存在的约束。我们采用参数模型更新的行星半径的基础上最近的测量，并使用互相关技术，以最大限度地提高灵敏度。我们的研究结果是一致的，是多云或含有少量的水和TiO的大气。使用这些参数模型，我们排除了平均分子量<= 15 g/mol的富水大气（VMR >= 0.1%），在3 sigma置信水平下，比以前的限制有了显着的改善。对于TiO，当VMR大于10^-8时，我们排除了平均分子量小于等于5 g/mol的可能性，置信度为3 sigma;当VMR大于10^-7时，我们的限值上升到平均分子量小于等于10 g/mol。我们可以排除低平均分子量的化学平衡模型，包括和排除TiO/VO在非常高的置信水平（> 10西格玛）。总的来说，我们的结果与具有高平均分子量和/或云，或没有大气的大气是一致的。
英文摘要：
The nearby super-Earth 55 Cnc e orbits a bright (V = 5.95 mag) star with a period of ~ 18 hours and a mass of ~ 8 Earth masses. Its atmosphere may be water-rich and have a large scale-height, though attempts to characterize it have yielded ambiguous results. Here we present a sensitive search for water and TiO in its atmosphere at high spectral resolution using the Gemini North telescope and the GRACES spectrograph. We combine observations with previous observations from Subaru and CFHT, improving the constraints on the presence of water vapor. We adopt parametric models with an updated planet radius based on recent measurements, and use a cross-correlation technique to maximize sensitivity. Our results are consistent with atmospheres that are cloudy or contain minimal amounts of water and TiO. Using these parametric models, we rule out a water-rich atmosphere (VMR >= 0.1%) with a mean molecular weight of <= 15 g/mol at a 3 sigma confidence level, improving on the previous limit by a significant margin. For TiO, we rule out a mean molecular weight of <= 5 g/mol with a 3 sigma confidence level for a VMR greater than 10^-8; for a VMR of greater than 10^-7, the limit rises to a mean molecular weight of <= 10 g/mol. We can rule out low mean-molecular-weight chemical equilibrium models both including and excluding TiO/VO at very high confidence levels (> 10 sigma). Overall, our results are consistent with an atmosphere with a high mean molecular weight and/or clouds, or no atmosphere.
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