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arXiv 2004.07252astro-ph.EP
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超高温超导体中的H-与离解--WASP-18 b的反演实例研究

H- and Dissociation in Ultra-hot Jupiters: A Retrieval Case Study of WASP-18b

Siddharth Gandhi, Nikku Madhusudhan, Avi Mandell

备注：
19 pages, 10 figures, accepted for publication in The Astronomical Journal
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摘要：

最近观测到了一些温度为$\gtrsim$ 2000~K的超高温超导体（UHJ）的大气。这些行星中的许多在HST WFC 3摄谱仪观测到的近红外光谱（1.1-1.7~ $μ$ m）中显示出很大程度上没有特征的热光谱，尽管这个光谱范围包含很强的H $_2$ O不透明度。最近的工作提出了H-不透明性掩盖H $_2$ O特征和/或H $_2$ O的热解离导致其在UHJ的高温下明显耗尽的可能性。在这项工作中，我们测试这些假设使用观测的系外行星WASP-18 b作为案例研究。我们报告详细的大气检索的行星使用Hyperion检索代码，扩展到包括H-不透明度和热离解的影响。我们报告的H $_2$ O，CO和H-丰度的限制，以及压力-温度剖面的昼侧大气检索和没有H-/解离每个数据集。我们发现，H $_2$ O和H-丰度是相对不受约束的无特征的WFC 3光谱。我们没有最终检测到H-在地球上相反，以前的研究使用平衡模型来推断它的存在。对CO丰度的限制取决于WFC 3和斯皮策数据的组合，范围从太阳到超级太阳CO值。我们还从两个数据集中看到了热反转的迹象。我们的研究表明了UHJs的大气反演的潜力，包括H-和分子的热解离的影响。

英文摘要：

Atmospheres of a number of ultra-hot Jupiters (UHJs) with temperatures $\gtrsim$2000~K have been observed recently. Many of these planets show largely featureless thermal spectra in the near-infrared observed with the HST WFC3 spectrograph (1.1-1.7~$μ$m) even though this spectral range contains strong H$_2$O opacity. Recent works have proposed the possibility of H- opacity masking the H$_2$O feature and/or thermal dissociation of H$_2$O causing its apparent depletion at the high temperatures of UHJs. In this work we test these hypotheses using observations of the exoplanet WASP-18b as a case study. We report detailed atmospheric retrievals of the planet using the HyDRA retrieval code, extended to include the effects of H- opacity and thermal dissociation. We report constraints on the H$_2$O, CO and H- abundances as well as the pressure-temperature profile of the dayside atmosphere for retrievals with and without H-/dissociation for each dataset. We find that the H$_2$O and H- abundances are relatively unconstrained given the featureless WFC3 spectra. We do not conclusively detect H- in the planet contrary to previous studies which used equilibrium models to infer its presence. The constraint on the CO abundance depends on the combination of WFC3 and Spitzer data, ranging from solar to super-solar CO values. We additionally see signs of a thermal inversion from two of the datasets. Our study demonstrates the potential of atmospheric retrievals of UHJs including the effects of H- and thermal dissociation of molecules.

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