Atmospheric studies of spectroscopically accessible terrestrial exoplanets lay the groundwork for comparative planetology between these worlds and the Solar System terrestrial planets. LHS 3844b is a highly-irradiated terrestrial exoplanet (R=1.303+/-0.022R_Earth) orbiting a mid-M dwarf 15 parsecs away. Work based on near-infrared Spitzer phase curves ruled out atmospheres with surface pressures >/=10 bars on this planet. We present 13 transit observations of LHS 3844b taken with the Magellan Clay telescope and the LDSS3C multi-object spectrograph covering 620-1020 nm. We analyze each of the 13 data sets individually using a Gaussian process regression, and present both white and spectroscopic light curves. In the combined white light curve we achieve an RMS precision of 65 ppm when binning to 10-minutes. The mean white light curve value of (Rp/Rs)^2 is 0.4170+/-0.0046%. To construct the transmission spectrum, we split the white light curves into 20 spectrophotometric bands, each spanning 20 nm, and compute the mean values of (Rp/Rs)^2 in each band. We compare the transmission spectrum to two sets of atmospheric models. We disfavor a clear, solar composition atmosphere (mu=2.34) with surface pressures >/=0.1 bar to 5.2-sigma confidence. We disfavor a clear, H2O steam atmosphere (mu=18) with surface pressures >/=0.1 bar to low confidence (2.9-sigma). Our observed transmission spectrum favors a flat line. For solar composition atmospheres with surface pressures >/=1 bar we rule out clouds with cloud-top pressures of 0.1 bar (5.3-sigma), but we cannot address high-altitude clouds at lower pressures. Our results add further evidence that LHS 3844b is devoid of an atmosphere.

中文翻译：

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来自 13 个地面传输观测的类地系外行星 LHS 3844b 的光学传输光谱

对光谱可用的类地系外行星的大气研究为这些世界与太阳系类地行星之间的比较行星学奠定了基础。LHS 3844b 是一颗受到高度辐射的类地系外行星 (R=1.303+/-0.022R_Earth)，它围绕 15 秒差距外的中 M 矮星运行。基于近红外斯皮策相位曲线的工作排除了这个星球上表面压力 >/=10 巴的大气。我们展示了用麦哲伦粘土望远镜和 LDSS3C 多目标光谱仪对 LHS 3844b 进行的 13 次凌日观测，覆盖范围为 620-1020 nm。我们使用高斯过程回归分别分析了 13 个数据集的每一个，并呈现了白色和光谱光曲线。在组合白光曲线中，当分档到 10 分钟时，我们实现了 65 ppm 的 RMS 精度。(Rp/Rs)^2 的平均白光曲线值为 0.4170+/-0.0046%。为了构建透射光谱，我们将白光曲线分成 20 个分光光度波段，每个波段跨越 20 nm，并计算每个波段中 (Rp/Rs)^2 的平均值。我们将传输光谱与两组大气模型进行比较。我们不喜欢表面压力 >/=0.1 bar 至 5.2-sigma 置信度的清晰的太阳组成大气 (mu=2.34)。我们不喜欢表面压力 >/=0.1 bar 的清澈 H2O 蒸汽气氛 (mu=18) 至低置信度 (2.9-sigma)。我们观察到的透射光谱有利于一条平坦的线。对于表面压力 >/=1 bar 的太阳组成大气，我们排除了云顶压力为 0.1 bar (5.3-sigma) 的云，但我们无法解决低压下的高空云。