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ARES I: WASP-76 b, A Tale of Two HST Spectra

Billy Edwards 1 Quentin Changeat 1 Robin Baeyens 2 Angelos Tsiaras 1 Ahmed Al-Refaie 1 Jake Taylor 3 Kai Hou Yip 1 Michelle Fabienne Bieger 4 Doriann Blain 5 Amélie Gressier 5, 6, 7 Gloria Guilluy 8, 9 Adam Yassin Jaziri 10 Flavien Kiefer 6 Darius Modirrousta-Galian 11, 12 Mario Morvan 1 Lorenzo Mugnai 13 William Pluriel 14 Mathilde Poveda 15, 16 Nour Skaf 1, 5 Niall Whiteford 17, 18 Sam Wright 1 Tiziano Zingales 10 Benjamin Charnay 5 Pierre Drossart 5 Jérémy Leconte 10 Olivia Venot 15 Ingo Waldmann 1 Jean-Philippe Beaulieu 6, 19
Abstract : We analyze the transmission and emission spectra of the ultra-hot Jupiter WASP-76 b, observed with the G141 grism of the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3). We reduce and fit the raw data for each observation using the open-source software Iraclis before performing a fully Bayesian retrieval using the publicly available analysis suite TauREx 3. Previous studies of the WFC3 transmission spectra of WASP-76 b found hints of titanium oxide (TiO) and vanadium oxide (VO) or non-gray clouds. Accounting for a fainter stellar companion to WASP-76, we reanalyze this data and show that removing the effects of this background star changes the slope of the spectrum, resulting in these visible absorbers no longer being detected, eliminating the need for a non-gray cloud model to adequately fit the data but maintaining the strong water feature previously seen. However, our analysis of the emission spectrum suggests the presence of TiO and an atmospheric thermal inversion, along with a significant amount of water. Given the brightness of the host star and the size of the atmospheric features, WASP-76 b is an excellent target for further characterization with HST, or with future facilities, to better understand the nature of its atmosphere, to confirm the presence of TiO and to search for other optical absorbers.
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Submitted on : Saturday, June 13, 2020 - 6:56:00 PM
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Billy Edwards, Quentin Changeat, Robin Baeyens, Angelos Tsiaras, Ahmed Al-Refaie, et al.. ARES I: WASP-76 b, A Tale of Two HST Spectra. Astronomical Journal, American Astronomical Society, 2020, 160 (1), pp.8. ⟨10.3847/1538-3881/ab9225⟩. ⟨insu-02867199⟩



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