文章基本信息

标题：H- and Dissociation in Ultra-hot Jupiters: A Retrieval Case Study of WASP-18b
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作者：Siddharth Gandhi ; Nikku Madhusudhan ; Avi Mandell 等
期刊名称：The Astronomical journal
印刷版ISSN：0004-6256
电子版ISSN：1538-3881
出版年度：2020
卷号：159
期号：5
页码：3152-3166
DOI：10.3847/1538-3881/ab845e
语种：English
出版社：American Institute of Physics
摘要：Atmospheres of a number of ultra-hot Jupiters (UHJs) with temperatures gsim2000 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 μm) even though this spectral range contains strong H2O opacity.Recent works have proposed the possibility of H- opacity masking the H2O feature and/or thermal dissociation of H2O 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 H2O, CO, and H- abundances as well as the pressure–temperature profile of the dayside atmosphere for retrievals with and without H-/dissociation for each data set.We find that the H2O and H- abundances are relatively unconstrained given the featureless WFC3 spectra.We do not conclusively detect H- in the planet, contrary to previous studies that 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 data sets.Our study demonstrates the potential of atmospheric retrievals of UHJs, including the effects of H- and thermal dissociation of molecules.
关键词：Exoplanet atmospheres;Spectroscopy;Radiative transfer;Hot Jupiters;Exoplanets