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 (10) , Mathilde Poveda (14, 15) , Nour Skaf (1, 5) , Niall Whiteford (16, 17) , Sam Wright (1) , Tiziano Zingales (10) , Benjamin Charnay (5) , Pierre Drossart (5) , Jérémy Leconte (10) , Olivia Venot (14) , Ingo Waldmann (1) , Jean-Philippe Beaulieu (6, 18)

1 Department of Physics and Astronomy [UCL London]
2 Instituut voor Sterrenkunde [Leuven]
3 AOPP - Department of Atmospheric, Oceanic and Planetary Physics [Oxford]
4 EMPS - College of Engineering, Mathematics and Physical Sciences [Exeter]
5 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics
6 IAP - Institut d'Astrophysique de Paris
7 PLANETO - LATMOS
8 Dipartimento di Fisica [Torino]
9 OATo - INAF - Osservatorio Astrofisico di Torino
10 ECLIPSE 2020
11 OAPa - INAF - Osservatorio Astronomico di Palermo
12 DiFC - Dipartimento di Fisica e Chimica [Palermo]
13 Dipartimento di Fisica [Roma La Sapienza]
14 LISA (UMR_7583) - Laboratoire Interuniversitaire des Systèmes Atmosphériques
15 MDLS - Maison de la Simulation
16 IfA - Institute for Astronomy [Edinburgh]
17 Centre for Exoplanet Science
18 School of Physical Sciences [Hobart]

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.

Domaines: Planète et Univers [physics]; Astrophysique [astro-ph]

Billy Edwards, Quentin Changeat, Robin Baeyens, Angelos Tsiaras, Ahmed Al-Refaie, et al.. ARES I: WASP-76 b, A Tale of Two HST Spectra. The Astronomical Journal, 2020, 160 (1), pp.8. ⟨10.3847/1538-3881/ab9225⟩. ⟨insu-02867199⟩