再次访问Eps Ind Ab：JWST新光度学数据证实了氨并暗示了气态巨行星大气层中厚云
A second visit to Eps Ind Ab with JWST: new photometry confirms ammonia and suggests thick clouds in the exoplanet atmosphere of the closest super-Jupiter
AI总结：
JWST观测证实Eps Ind Ab大气中存在氨并暗示厚云，重新拟合轨道并发现更新的质量和偏心率。
摘要：
利用JWST，我们首次直接成像冷（约200-300K）的太阳年龄巨行星。在这些温度下，许多分子特征会出现，水冰云可能凝结并影响发射光谱；早期的光度学测量已经显示出与无云、太阳金属丰度大气模型预测之间的一些矛盾。在这里，我们呈现了JWST/MIRI冠状仪观测的冷巨行星Eps Ind Ab在11.3um的新观测结果。结合存档数据，我们利用这些新观测研究该冷巨行星的大气，并重新拟合其轨道，发现更新的质量为7.6±0.7Mj和偏心率0.24±0.11。该行星在11.3um处比在10.6um处明亮0.88±0.08mag，表明存在氨。然而，这个氨特征比预期的要浅。这可能表明低金属丰度或氮贫乏的大气层，但我们的首选解释是存在厚水冰云，这些云抑制了氨特征和Eps Ind Ab的近红外发射。对小但逐渐增长的冷巨行星样本的光度学研究显示，它们在3到5um之间普遍比预期更暗，这与水冰云假说一致。该冷巨行星样本在10.6um和11.3um的光度学数据将有助于确定是否抑制的氨特征是普遍的，并提出关于底层物理原因的新开放问题。
英文摘要：
With JWST, we are directly imaging cold (~200-300K), solar-age giant exoplanets for the first time. At these temperatures many molecular features appear and water-ice clouds may condense and affect the emission spectrum; early photometric measurements of cold giant planets are already showing some tension with the predictions of cloud-free, solar-metallicity atmosphere models. Here we present new JWST/MIRI coronagraphic observations of the cold giant exoplanet Eps Ind Ab at 11.3um. Together with archival data, we use these new observations to study the atmosphere of this cold exoplanet, and we also re-fit its orbit, finding an updated mass of $7.6\pm0.7$ Mj and an eccentricity of $0.24^{+0.11}_{-0.08}$. The planet is significantly brighter (by $0.88\pm0.08$ mag) at 11.3um than at 10.6um, indicating the presence of ammonia. However, this ammonia feature is shallower than expected. This could indicate a low-metallicity or nitrogen-depleted atmosphere, but our preferred explanation is the presence of thick water-ice clouds that suppress the ammonia feature and the near-IR emission of Eps Ind Ab. Photometry of the small but growing sample of cold, giant exoplanets demonstrates that they are consistently fainter than expected between 3 to 5um, consistent with the water-ice cloud hypothesis. 10.6um and 11.3um photometry of this cold exoplanet sample would be valuable to determine whether the suppressed ammonia feature is universal, and to frame a new open question about the underlying physical cause.
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