An Unusual Transmission Spectrum for the Sub-Saturn KELT-11b Suggestive of a Subsolar Water Abundance
An Unusual Transmission Spectrum for the Sub-Saturn KELT-11b Suggestive of a Subsolar Water Abundance
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DOI：
10.3847/1538-3881/abc1e9
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发表时间：
2020-05
期刊：
影响因子：
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通讯作者：
K. Colón;L. Kreidberg;L. Welbanks;M. Line;N. Madhusudhan;T. Beatty;P. Tamburo;K. Stevenson;
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文献类型：
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作者：
K. Colón;L. Kreidberg;L. Welbanks;M. Line;N. Madhusudhan;T. Beatty;P. Tamburo;K. Stevenson;
我们提出了一个膨胀的sub-Saturn KELT-11b的光学到红外透射光谱测量凌日系外行星调查卫星（TESS），哈勃太空望远镜（HST）宽视场相机3 G141分光棱镜，和斯皮策太空望远镜（斯皮策）在3.6 μm，除了斯皮策4.5 μm的二次日食。精确的HST透射光谱显着揭示了一个不寻常的形状低振幅的水功能。基于不同的分子丰度的免费检索分析，我们发现强有力的证据吸水。根据模型的假设，我们还发现其他吸收剂（HCN，TiO和AlO）的初步证据。反演的水丰度一般为0.001-0.7倍太阳能（在一系列模型假设中为0.001-0.7倍太阳能），比基于太阳系金属丰度趋势的行星形成模型的预期低几个数量级。我们还考虑了化学平衡和自洽的一维辐射-对流平衡模型拟合，发现它们也倾向于低金属丰度（[M/H] m −2，与自由检索结果一致）。然而，所有的检索都应谨慎解释，因为它们要么需要远远超出化学平衡的额外吸收剂来解释光谱的形状，要么只是与数据拟合不佳。最后，我们发现，斯皮策二次日食是充分的热量重新分配从KELT-11b的昼侧到夜侧的指示，假设一个明确的昼侧。KELT-11b组成的这些可能不寻常的结果表明，面对越来越精确的系外行星光谱测量，大气和形成模型面临着新的挑战。
We present an optical-to-infrared transmission spectrum of the inflated sub-Saturn KELT-11b measured with the Transiting Exoplanet Survey Satellite (TESS), the Hubble Space Telescope (HST) Wide Field Camera 3 G141 spectroscopic grism, and the Spitzer Space Telescope (Spitzer) at 3.6 μm, in addition to a Spitzer 4.5 μm secondary eclipse. The precise HST transmission spectrum notably reveals a low-amplitude water feature with an unusual shape. Based on free-retrieval analyses with varying molecular abundances, we find strong evidence for water absorption. Depending on model assumptions, we also find tentative evidence for other absorbers (HCN, TiO, and AlO). The retrieved water abundance is generally ≲0.1× solar (0.001–0.7× solar over a range of model assumptions), several orders of magnitude lower than expected from planet formation models based on the solar system metallicity trend. We also consider chemical-equilibrium and self-consistent 1D radiative-convective equilibrium model fits and find that they, too, prefer low metallicities ([M/H] ≲ −2, consistent with the free-retrieval results). However, all of the retrievals should be interpreted with some caution because they either require additional absorbers that are far out of chemical equilibrium to explain the shape of the spectrum or are simply poor fits to the data. Finally, we find that the Spitzer secondary eclipse is indicative of full heat redistribution from KELT-11b’s dayside to nightside, assuming a clear dayside. These potentially unusual results for KELT-11b’s composition are suggestive of new challenges on the horizon for atmosphere and formation models in the face of increasingly precise measurements of exoplanet spectra.