Detection of the tidal deformation of WASP-103b at 3 σ with CHEOPS

Author(s): S. C.C. Barros, B. Akinsanmi, G. Boué, A. M.S. Smith, J. Laskar, S. Ulmer-Moll, J. Lillo-Box, D. Queloz, A. Collier Cameron, S. G. Sousa, D. Ehrenreich, M. J. Hooton, G. Bruno, B. O. Demory, A. C.M. Correia, O. D.S. Demangeon, T. G. Wilson, A. Bonfanti, S. Hoyer, Y. Alibert, R. Alonso, G. Anglada Escudé, D. Barbato, T. Bárczy, D. Barrado, W. Baumjohann, M. Beck, T. Beck, W. Benz, M. Bergomi, N. Billot, X. Bonfils, F. Bouchy, A. Brandeker, C. Broeg, J. Cabrera, V. Cessa, S. Charnoz, C. C.V. Damme, M. B. Davies, M. Deleuil, A. Deline, L. Delrez, A. Erikson, A. Fortier, M. Fridlund, D. Gandolfi, A. García Muñoz, M. Gillon, M. Güdel, K. G. Isaak, K. Heng, L. Kiss, A. Lecavelier Des Etangs, M. Lendl, C. Lovis, D. Magrin, V. Nascimbeni, P. F.L. Maxted, G. Olofsson, R. Ottensamer, I. Pagano, E. Pallé, H. Parviainen, G. Peter, G. Piotto, D. Pollacco, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, N. C. Santos, G. Scandariato, D. Ségransan, A. E. Simon, M. Steller, Gy M. Szabó, N. Thomas, S. Udry, B. Ulmer, V. Van Grootel, Luca Fossati, N. A. Walton
Abstract: Context. Ultra-short period planets undergo strong tidal interactions with their host star which lead to planet deformation and orbital tidal decay. Aims. WASP-103b is the exoplanet with the highest expected deformation signature in its transit light curve and one of the shortest expected spiral-in times. Measuring the tidal deformation of the planet would allow us to estimate the second degree fluid Love number and gain insight into the planet's internal structure. Moreover, measuring the tidal decay timescale would allow us to estimate the stellar tidal quality factor, which is key to constraining stellar physics. Methods. We obtained 12 transit light curves of WASP-103b with the CHaracterising ExOplanet Satellite (CHEOPS) to estimate the tidal deformation and tidal decay of this extreme system. We modelled the high-precision CHEOPS transit light curves together with systematic instrumental noise using multi-dimensional Gaussian process regression informed by a set of instrumental parameters. To model the tidal deformation, we used a parametrisation model which allowed us to determine the second degree fluid Love number of the planet. We combined our light curves with previously observed transits of WASP-103b with the Hubble Space Telescope (HST) and Spitzer to increase the signal-to-noise of the light curve and better distinguish the minute signal expected from the planetary deformation. Results. We estimate the radial Love number of WASP-103b to be hf = 1.59-0.53+0.45. This is the first time that the tidal deformation is directly detected (at 3 σ) from the transit light curve of an exoplanet. Combining the transit times derived from CHEOPS, HST, and Spitzer light curves with the other transit times available in the literature, we find no significant orbital period variation for WASP-103b. However, the data show a hint of an orbital period increase instead of a decrease, as is expected for tidal decay. This could be either due to a visual companion star if this star is bound, the Applegate effect, or a statistical artefact. Conclusions. The estimated Love number of WASP-103b is similar to Jupiter's. This will allow us to constrain the internal structure and composition of WASP-103b, which could provide clues on the inflation of hot Jupiters. Future observations with James Webb Space Telescope can better constrain the radial Love number of WASP-103b due to their high signal-to-noise and the smaller signature of limb darkening in the infrared. A longer time baseline is needed to constrain the tidal decay in this system.
Organisation(s): Department of Astrophysics
External organisation(s): Universidade do Porto, Université de Genève, Université de recherche Paris Sciences et Lettres, Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), European Space Astronomy Centre (ESA), University of Cambridge, University of St. Andrews, Universität Bern, INAF-Osservatorio Astrofisico di Catania, Universidade de Coimbra, Österreichische Akademie der Wissenschaften (ÖAW), 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., Osservatorio Astronomico, University of Grenoble Alpes, Stockholm University, Université Paris VII - Paris-Diderot, Science and Operations Department - Science Division (SCI-SC), Lund University, Aix-Marseille Université, Université de Liège, Chalmers University of Technology, Leiden University, University of Turin, Technische Universität Berlin, University of Warwick, Eötvös Loránd Research Network, The University of Sydney, Université Paris VI - Pierre-et-Marie-Curie, Keele University, University of Padova, Freie Universität Berlin (FU), Eötvös Loránd University Budapest, Ingenieurbüro Ulmer
Journal: Astronomy and Astrophysics
Volume: 657
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/202142196
Publication date: 01-2022
Peer reviewed: Yes
Austrian Fields of Science 2012: 103004 Astrophysics, 103003 Astronomy, 103038 Space exploration
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/9cbf6d62-0ff1-489c-8fb9-2d4e410f73e6

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