The geometric albedo of the hot Jupiter HD 189733b measured with CHEOPS

Author(s): A. F. Krenn, M. Lendl, J. A. Patel, L. Carone, M. Deleuil, S. Sulis, A. Collier Cameron, A. Deline, P. Guterman, D. Queloz, L. Fossati, A. Brandeker, K. Heng, B. Akinsanmi, V. Adibekyan, A. Bonfanti, O. D.S. Demangeon, D. Kitzmann, S. Salmon, S. G. Sousa, T. G. Wilson, Y. Alibert, R. Alonso, G. Anglada, T. Bárczy, D. Barrado Navascues, S. C.C. Barros, W. Baumjohann, M. Beck, T. Beck, W. Benz, N. Billot, L. Blecha, X. Bonfils, L. Borsato, C. Broeg, J. Cabrera, S. Charnoz, C. Corral Van Damme, Sz Csizmadia, P. E. Cubillos, M. B. Davies, L. Delrez, B. O. Demory, D. Ehrenreich, A. Erikson, J. Farinato, A. Fortier, M. Fridlund, D. Gandolfi, M. Gillon, M. Güdel, S. Hoyer, K. G. Isaak, L. L. Kiss, E. Kopp, J. Laskar, A. Lecavelier Des Etangs, C. Lovis, D. Magrin, P. F.L. Maxted, C. Mordasini, V. Nascimbeni, G. Olofsson, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, G. Piotto, D. Pollacco, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, N. C. Santos, G. Scandariato, D. Ségransan, A. E. Simon, A. M.S. Smith, M. Steller, Gy M. Szabó, N. Thomas, S. Udry, B. Ulmer, V. Van Grootel, J. Venturini, N. A. Walton
Abstract: 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.
Organisation(s): Department of Astrophysics
External organisation(s): Österreichische Akademie der Wissenschaften (ÖAW), Université de Genève, Stockholm University, Aix-Marseille Université, University of St. Andrews, National Institute for Earth Sciences & Astronomy (INSU-CNRS), Eidgenössische Technische Hochschule Zürich, University of Cambridge, Ludwig-Maximilians-Universität München, University of Warwick, Universität Bern, Universidade do Porto, Institute of Astrophysics of the Canary Islands, University of La Laguna, Spanish National Research Council (CSIC), Institute of Space Studies of Catalonia (IEEC), Admatis Ltd., European Space Astronomy Centre (ESA), Almatech SA, University of Grenoble Alpes, Osservatorio Astronomico, Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Université de Paris, Science and Operations Department - Science Division (SCI-SC), INAF-Osservatorio Astrofisico di Torino, Lund University, Université de Liège, Leiden University, Chalmers University of Technology, Università degli Studi di Torino, Eötvös Loránd Research Network, Eötvös Loránd University Budapest, Technische Universität Berlin, Freie Universität Berlin (FU), Université de recherche Paris Sciences et Lettres, Université Paris VI - Pierre-et-Marie-Curie, Keele University, INAF-Osservatorio Astrofisico di Catania, University of Padova
Journal: Astronomy and Astrophysics
Volume: 672
No. of pages: 16
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/202245016
Publication date: 04-2023
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics, 103038 Space exploration
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Sustainable Development Goals: SDG 3 - Good Health and Well-being
Portal url: https://ucrisportal.univie.ac.at/en/publications/0b56bf80-dba9-4711-bef4-2ef3454bd243

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