The atmosphere and architecture of WASP-189 b probed by its CHEOPS phase curve^★

¹ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
e-mail: adrien.deline@unige.ch
² Physikalisches Institut, University of Bern, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
³ Center for Space and Habitability, University of Bern, Gesellsschaftstrasse 6, 3012 Bern, Switzerland
⁴ Department of Astronomy, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden
⁵ Aix-Marseille Université, CNRS, CNES, Laboratoire d’Astrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388 Marseille, France
⁶ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
⁷ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁸ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
⁹ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹⁰ University Observatory Munich, Ludwig Maximilian University, Scheinerstraße 1, Munich 81679, Germany
¹¹ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
¹² Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹³ Dipartimento di Fisica, Università degli Studi di Torino, Via Pietro Giuria 1, 10125, Torino, Italy
¹⁴ INAF, Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
¹⁵ Space Research Institute, Austrian Academy of Sciences, Schmiedlstraße 6, 8042 Graz, Austria
¹⁶ Centre for Exoplanet Science, SUPA School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
¹⁷ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Barcelona, Spain
¹⁸ Admatis, Kandó Kálmán út 5, 3534 Miskolc, Hungary
¹⁹ Departamento de Astrofísica, Centro de Astrobiología (CSIC-INTA), ESAC campus, 28692 Villanueva de la Cañada, Spain
²⁰ Université Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble, 38000 Grenoble, France
²¹ Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstraße 2, 12489 Berlin, Germany
²² Université de Paris, Institut de Physique du Globe de Paris, CNRS, 75005 Paris, France
²³ European Space Research and Technology Centre (ESTEC), European Space Agency (ESA), Keplerlaan 1, 2201-AZ Noordwijk, The Netherlands
²⁴ Centre for Mathematical Sciences, Lund University, Box 118, 22100 Lund, Sweden
²⁵ Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
²⁶ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
²⁷ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
²⁸ Department of Astrophysics, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria
²⁹ Division Technique, Institut National des Sciences de l’Univers (INSU), CS 20330, 83507 La Seyne-sur-Mer, France
³⁰ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
³¹ IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL Université, Sorbonne Université, 77 avenue Denfert-Rochereau, 75014 Paris, France
³² Institut d’astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98 bis boulevard Arago, 75014 Paris, France
³³ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
³⁴ INAF, Osservatorio Astrofisico di Catania, Via Santa Sofia 78, 95123 Catania, Italy
³⁵ Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstraße 2, 12489 Berlin, Germany
³⁶ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università degli Studi di Padova, Vicolo Osservatorio 3, 35122 Padova, Italy
³⁷ Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
³⁸ Department of Physics, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
³⁹ Center for Astronomy and Astrophysics, Technical University Berlin, Hardenberstraße 36, 10623 Berlin, Germany
⁴⁰ Institut für Geologische Wissenschaften, Freie Universität Berlin, 12249 Berlin, Germany
⁴¹ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
⁴² ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, Szent Imre herceg utca 112, 9700 Szombathely, Hungary
⁴³ MTA-ELTE Exoplanet Research Group, Szent Imre herceg utca 112, 9700 Szombathely, Hungary
⁴⁴ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

Received: 8 October 2021
Accepted: 24 December 2021

Abstract

Context. Gas giants orbiting close to hot and massive early-type stars can reach dayside temperatures that are comparable to those of the coldest stars. These ‘ultra-hot Jupiters’ have atmospheres made of ions and atomic species from molecular dissociation and feature strong day-to-night temperature gradients. Photometric observations at different orbital phases provide insights on the planet’s atmospheric properties.

Aims. We aim to analyse the photometric observations of WASP-189 acquired with the Characterising Exoplanet Satellite (CHEOPS) to derive constraints on the system architecture and the planetary atmosphere.

Methods. We implemented a light-curve model suited for an asymmetric transit shape caused by the gravity-darkened photosphere of the fast-rotating host star. We also modelled the reflective and thermal components of the planetary flux, the effect of stellar oblateness and light-travel time on transit-eclipse timings, the stellar activity, and CHEOPS systematics.

Results. From the asymmetric transit, we measure the size of the ultra-hot Jupiter WASP-189 b, R_p = 1.600_−0.016^+0.017 R_J, with a precision of 1%, and the true orbital obliquity of the planetary system, Ψ_p = 89.6 ± 1.2deg (polar orbit). We detect no significant hotspot offset from the phase curve and obtain an eclipse depth of δ_ecl = 96.5_−5.0^+4.5 ppm, from which we derive an upper limit on the geometric albedo: A_g < 0.48. We also find that the eclipse depth can only be explained by thermal emission alone in the case of extremely inefficient energy redistribution. Finally, we attribute the photometric variability to the stellar rotation, either through superficial inhomogeneities or resonance couplings between the convective core and the radiative envelope.

Conclusions. Based on the derived system architecture, we predict the eclipse depth in the upcoming Transiting Exoplanet Survey Satellite (TESS) observations to be up to ~165 ppm. High-precision detection of the eclipse in both CHEOPS and TESS passbands might help disentangle reflective and thermal contributions. We also expect the right ascension of the ascending node of the orbit to precess due to the perturbations induced by the stellar quadrupole moment J₂ (oblateness).