The geometric albedo of the hot Jupiter HD 189733b measured with CHEOPS
Journal article, 2023
Context. Measurements of the occultation of an exoplanet at visible wavelengths allow us to determine the reflective properties of a planetary atmosphere. The observed occultation depth can be translated into a geometric albedo. This in turn aids in characterising the structure and composition of an atmosphere by providing additional information on the wavelength-dependent reflective qualities of the aerosols in the atmosphere. Aims. Our aim is to provide a precise measurement of the geometric albedo of the gas giant HD 189733b by measuring the occultation depth in the broad optical bandpass of CHEOPS (350-1100 nm). Methods. We analysed 13 observations of the occultation of HD 189733b performed by CHEOPS utilising the Python package PyCHEOPS. The resulting occultation depth is then used to infer the geometric albedo accounting for the contribution of thermal emission from the planet. We also aid the analysis by refining the transit parameters combining observations made by the TESS and CHEOPS space telescopes. Results. We report the detection of an 24.7 ± 4.5 ppm occultation in the CHEOPS observations. This occultation depth corresponds to a geometric albedo of 0.076 ± 0.016. Our measurement is consistent with models assuming the atmosphere of the planet to be cloud-free at the scattering level and absorption in the CHEOPS band to be dominated by the resonant Na doublet. Taking into account previous optical-light occultation observations obtained with the Hubble Space Telescope, both measurements combined are consistent with a super-stellar Na elemental abundance in the dayside atmosphere of HD 189733b. We further constrain the planetary Bond albedo to between 0.013 and 0.42 at 3σconfidence. Conclusions. We find that the reflective properties of the HD 189733b dayside atmosphere are consistent with a cloud-free atmosphere having a super-stellar metal content. When compared to an analogous CHEOPS measurement for HD 209458b, our data hint at a slightly lower geometric albedo for HD 189733b (0.076 ± 0.016) than for HD 209458b (0.096 ± 0.016), or a higher atmospheric Na content in the same modelling framework. While our constraint on the Bond albedo is consistent with previously published values, we note that the higher-end values of ∼0.4, as derived previously from infrared phase curves, would also require peculiarly high reflectance in the infrared, which again would make it more difficult to disentangle reflected and emitted light in the total observed flux, and therefore to correctly account for reflected light in the interpretation of those phase curves. Lower reported values for the Bond albedos are less affected by this ambiguity.
Techniques: photometric
Planets and satellites: atmospheres
Planets and satellites: individual: HD 189733b
Author
A. Krenn
University of Geneva
Institut fur Weltraumforschung
M. Lendl
University of Geneva
J. A. Patel
Stockholm University
L. Carone
Institut fur Weltraumforschung
M. Deleuil
Laboratoire d'Astrophysique de Marseille
S. Sulis
Laboratoire d'Astrophysique de Marseille
A. Collier Cameron
University of St Andrews
A. Deline
University of Geneva
P. Guterman
Laboratoire d'Astrophysique de Marseille
Institut National des Sciences de l'Univers
D. Queloz
Swiss Federal Institute of Technology in Zürich (ETH)
University of Cambridge
L. Fossati
Institut fur Weltraumforschung
A. Brandeker
Stockholm University
Kevin Heng
The University of Warwick
Ludwig Maximilian University of Munich (LMU)
University of Bern
B. Akinsanmi
University of Geneva
V. Adibekyan
University of Porto
A. Bonfanti
Institut fur Weltraumforschung
O. Demangeon
University of Porto
D. Kitzmann
University of Bern
S. Salmon
University of Geneva
S. G. Sousa
University of Porto
T. G. Wilson
University of St Andrews
Y. Alibert
University of Bern
R. Alonso
University of La Laguna
Instituto de Astrofísica de Canarias
G. Anglada
Spanish National Research Council (CSIC)
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
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
L. Blecha
ALMATECH SA
X. Bonfils
Institut de Planétologie et d’Astrophysique de Grenoble (IPAG)
L. Borsato
Istituto nazionale di astrofisica (INAF)
C. Broeg
University of Bern
J. Cabrera
German Aerospace Center (DLR)
S. Charnoz
Institut de Physique du Globe de Paris
C. Corral Van Damme
European Space Agency (ESA)
Szilard Csizmadia
German Aerospace Center (DLR)
P. E. Cubillos
Institut fur Weltraumforschung
Istituto nazionale di astrofisica (INAF)
M. B. Davies
Lund University
L. Delrez
University of Liège
B.O. Demory
University of Bern
D. Ehrenreich
University of Geneva
Anders Erikson
German Aerospace Center (DLR)
J. Farinato
Istituto nazionale di astrofisica (INAF)
A. Fortier
University of Bern
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
S. Hoyer
Laboratoire d'Astrophysique de Marseille
K. Isaak
European Space Agency (ESA)
L.L. Kiss
Eötvös Loránd University (ELTE)
Hungarian Academy of Sciences
E. Kopp
Freie Universität Berlin
German Aerospace Center (DLR)
Technische Universität Berlin
J. Laskar
Paris Observatory
A. L. des Etangs
Institut d 'Astrophysique de Paris
C. Lovis
University of Geneva
D. Magrin
Istituto nazionale di astrofisica (INAF)
P. Maxted
Keele University
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)
E. Palle
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
Roberto Ragazzoni
Istituto nazionale di astrofisica (INAF)
University of Padua
N. Rando
European Space Agency (ESA)
H. Rauer
Technische Universität Berlin
German Aerospace Center (DLR)
Freie Universität Berlin
I. Ribas
Spanish National Research Council (CSIC)
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)
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)
Manfred B. Steller
Institut fur Weltraumforschung
Gy M. Szabó
Eötvös Loránd University (ELTE)
N. Thomas
University of Bern
S. Udry
University of Geneva
B. Ulmer
German Aerospace Center (DLR)
Technische Universität Berlin
Freie Universität Berlin
V. Van Grootel
University of Liège
J. Venturini
University of Geneva
N. A. Walton
University of Cambridge
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 672 A24Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
Other Physics Topics
DOI
10.1051/0004-6361/202245016