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Scientific article
Open access
English

Asymmetry in the atmosphere of the ultra-hot Jupiter WASP-76 b

Published inAstronomy & astrophysics, vol. 684, p. 1-35; A27
Publication date2024-04-05
First online date2024-04-05
Abstract

Context: WASP-76 b has been a recurrent subject of study since the detection of a signature in high-resolution transit spectroscopy data indicating an asymmetry between the two limbs of the planet. The existence of this asymmetric signature has been confirmed by multiple studies, but its physical origin is still under debate. In addition, it contrasts with the absence of asymmetry reported in the infrared (IR) phase curve.

Aims: We provide a more comprehensive dataset of WASP-76 b with the goal of drawing a complete view of the physical processes at work in this atmosphere. In particular, we attempt to reconcile visible high-resolution transit spectroscopy data and IR broadband phase curves.

Methods: We gathered 3 phase curves, 20 occultations, and 6 transits for WASP-76 b in the visible with the CHEOPS space telescope. We also report the analysis of three unpublished sectors observed by the TESS space telescope (also in the visible), which represents 34 phase curves.

Results: WASP-76 b displays an occultation of 260 ± 11 and 152 ± 10 ppm in TESS and CHEOPS bandpasses respectively. Depending on the composition assumed for the atmosphere and the data reduction used for the IR data, we derived geometric albedo estimates that range from 0.05 ± 0.023 to 0.146 ± 0.013 and from <0.13 to 0.189 ± 0.017 in the CHEOPS and TESS bandpasses, respectively. As expected from the IR phase curves, a low-order model of the phase curves does not yield any detectable asymmetry in the visible either. However, an empirical model allowing for sharper phase curve variations offers a hint of a flux excess before the occultation, with an amplitude of ~40 ppm, an orbital offset of ~ −30°, and a width of ~20º. We also constrained the orbital eccentricity of WASP-76 b to a value lower than 0.0067, with a 99.7% confidence level. This result contradicts earlier proposed scenarios aimed at explaining the asymmetry observed in high-resolution transit spectroscopy.

Conclusions: In light of these findings, we hypothesise that WASP-76 b could have night-side clouds that extend predominantly towards its eastern limb. At this limb, the clouds would be associated with spherical droplets or spherically shaped aerosols of an unknown species, which would be responsible for a glory effect in the visible phase curves.

eng
Keywords
  • Techniques: photometric
  • Planets and satellites: atmospheres
  • Planets and satellites: composition
Funding
  • Fundação para a Ciência e a Tecnologia, I.P. - Characterisation of Earth-size transiting planets [IF/01312/2014/CP1215/CT0004]
  • UK Research and Innovation - Astronomy at St Andrews 2018-2021 [ST/R000824/1]
  • UK Research and Innovation - Astronomy at St Andrews 2021 - 2024 [ST/V000861/1]
  • Fundação para a Ciência e a Tecnologia, I.P. - Institute of Astrophysics and Space Sciences [UIDP/04434/2020]
  • European Commission - Alexander von Humboldt and the Globalization of Science: Networks of Knowledge between Germany and the United States in the 19th Century [327127]
  • Fundação para a Ciência e a Tecnologia, I.P. - Star-exoplanet compositional link: towards realistic characterization of terrestrial planets [2022.06962.PTDC]
  • UK Research and Innovation - Astrophysics at Keele: planets, stars and galaxies. [ST/M001040/1]
  • European Commission - FInding ExoeaRths: tackling the ChallengEs of stellar activity [101052347]
  • Fundação para a Ciência e a Tecnologia, I.P. - Institute of Astrophysics and Space Sciences [UIDB/04434/2020]
  • European Commission - Virtual Laboratories for Exoplanets and Planet Forming Disks [860470]
  • European Commission - Future of upper atmospheric characterisation of exoplanets with spectroscopy [724427]
Citation (ISO format)
DEMANGEON, Olivier D.S. et al. Asymmetry in the atmosphere of the ultra-hot Jupiter WASP-76 b. In: Astronomy & astrophysics, 2024, vol. 684, p. 1–35. doi: 10.1051/0004-6361/202348270
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Article (Published version)
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ISSN of the journal0004-6361
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