Asymmetry in the atmosphere of the ultra-hot Jupiter WASP-76 b***
Journal article, 2024
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 We also report the analysis of three unpublished sectors observed by the TESS space telescope (also in the visible), which represents 34 phase curves.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 ∼20◦. 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.
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 ∼20◦. 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.
planets and satellites: atmospheres
planets
satellites: composition
techniques: photometric
Author
O. Demangeon
University of Porto
P. E. Cubillos
Istituto nazionale di astrofisica (INAF)
Institut fur Weltraumforschung
V. Singh
Istituto nazionale di astrofisica (INAF)
T.G. Wilson
The University of Warwick
L. Carone
Institut fur Weltraumforschung
A. Bekkelien
University of Geneva
A. Deline
University of Geneva
D. Ehrenreich
University of Geneva
P. Maxted
Keele University
B.O. Demory
University of Bern
Tiziano Zingales
Istituto nazionale di astrofisica (INAF)
University of Padua
M. Lendl
University of Geneva
A. Bonfanti
Institut fur Weltraumforschung
S. G. Sousa
University of Porto
A. Brandeker
Stockholm University
Y. Alibert
University of Bern
R. Alonso
University of La Laguna
Instituto de Astrofísica de Canarias
J. Asquier
European Space Research and Technology Centre (ESA ESTEC)
T. Bárczy
Admatis
D. Barrado Navascues
Centro de Astrobiologia (CAB)
S.C.C. Barros
University of Porto
W. Baumjohann
Institut fur Weltraumforschung
M. Beck
University of Geneva
T. Beck
University of Bern
W. Benz
University of Bern
N. Billot
University of Geneva
F. Biondi
Istituto nazionale di astrofisica (INAF)
Max Planck Society
L. Borsato
Istituto nazionale di astrofisica (INAF)
C. Broeg
University of Bern
M. Buder
German Aerospace Center (DLR)
A. Collier Cameron
University of St Andrews
Szilard Csizmadia
German Aerospace Center (DLR)
M. B. Davies
Lund University
M. Deleuil
Laboratoire d'Astrophysique de Marseille
L. Delrez
University of Liège
Anders Erikson
German Aerospace Center (DLR)
A. Fortier
University of Bern
L. Fossati
Institut fur Weltraumforschung
Malcolm Fridlund
Leiden University
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
D. Gandolfi
University of Turin
Michaël Gillon
University of Liège
M. Gudel
University of Vienna
Maximilian N. Günther
European Space Research and Technology Centre (ESA ESTEC)
A. Heitzmann
University of Geneva
Ch. Helling
Institut fur Weltraumforschung
Technische Universität Graz
S. Hoyer
Laboratoire d'Astrophysique de Marseille
K. Isaak
European Space Research and Technology Centre (ESA ESTEC)
L. L. Kiss
Eötvös Loránd University (ELTE)
Hungarian Academy of Sciences
K. W.F. Lam
German Aerospace Center (DLR)
J. Laskar
Paris Observatory
A. L. des Etangs
Institut d 'Astrophysique de Paris
D. Magrin
Istituto nazionale di astrofisica (INAF)
M. Mecina
University of Vienna
C. Mordasini
University of Bern
Valerio Nascimbeni
Istituto nazionale di astrofisica (INAF)
G. Olofsson
Stockholm University
R. Ottensamer
University of Vienna
I. Pagano
Istituto nazionale di astrofisica (INAF)
Enric Palle
University of La Laguna
Instituto de Astrofísica de Canarias
G. Peter
German Aerospace Center (DLR)
Giampaolo P. Piotto
Istituto nazionale di astrofisica (INAF)
University of Padua
D. Pollacco
The University of Warwick
D. Queloz
Swiss Federal Institute of Technology in Zürich (ETH)
University of Cambridge
R. Ragazzoni
Istituto nazionale di astrofisica (INAF)
University of Padua
N. Rando
European Space Research and Technology Centre (ESA ESTEC)
H. Rauer
German Aerospace Center (DLR)
Freie Universität Berlin
Technische Universität Berlin
I. Ribas
Institute of Space Studies of Catalonia (IEEC)
Institute of Space Sciences (ICE) - CSIC
M. Rieder
University of Bern
S. Salmon
University of Geneva
N. C. Santos
University of Porto
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
D. Segransan
University of Geneva
A.E. Simon
University of Bern
A. M.S. Smith
German Aerospace Center (DLR)
M. Stalport
University of Liège
G.M. Szabó
HUN-REN-ELTE Exoplanet Research Group
Eötvös Loránd University (ELTE)
Nicolas Thomas
University of Bern
S. Udry
University of Geneva
V. Van Grootel
University of Liège
J. Venturini
University of Geneva
E. Villaver
Instituto de Astrofísica de Canarias
University of La Laguna
N. A. Walton
University of Cambridge
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 684 A27Subject Categories
Astronomy, Astrophysics and Cosmology
Infrastructure
Onsala Space Observatory
DOI
10.1051/0004-6361/202348270