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 10 sigma). Overall, our results are consistent with an atmosphere with a high mean molecular weight and/or clouds, or no atmosphere.

中文翻译：

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使用高分辨率地基光谱表征超级地球 55 Cancri e 的大气层

附近的超级地球 55 Cnc e 围绕一颗明亮的（V = 5.95 mag）恒星运行，周期约为 18 小时，质量约为地球质量的 8。它的大气层可能富含水并且具有很大的尺度高度，尽管试图描述它的特征已经产生了模棱两可的结果。在这里，我们使用 Gemini North 望远镜和 GRACES 光谱仪以高光谱分辨率对大气中的水和二氧化钛进行了敏感搜索。我们将观察结果与之前斯巴鲁和 CFHT 的观察结果相结合，改善了对水蒸气存在的限制。我们采用基于最近测量结果更新行星半径的参数模型，并使用互相关技术来最大化灵敏度。我们的结果与多云或含有少量水和二氧化钛的大气一致。使用这些参数模型，我们排除了平均分子量为 10 西格玛的富含水的大气（VMR >= 0.1%）。总体而言，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一致。