The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS^★

¹ Observatoire de Genève, Université de Genève, Chemin des maillettes 51, 1290 Sauverny, Switzerland
e-mail: Monika.Lendl@unige.ch
² Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
³ Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstr. 2, 12489, Berlin, Germany
⁴ Center for Space and Habitability, Gesellsschaftstr. 6, 3012 Bern, Switzerland
⁵ Laboratoire d’Astrophysique de Marseille, Univ. de Provence, UMR6110 CNRS, 38 r. F. Joliot Curie, 13388 Marseille, France
⁶ Physikalisches Institut, University of Bern, Gesellschaftsstr. 6, 3012 Bern, Switzerland
⁷ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium
⁸ Astrophysics Group, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
⁹ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
¹⁰ Department of Astronomy, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden
¹¹ School of Physics and Astronomy, Physical Science Building, North Haugh, St Andrews, UK
¹² Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
¹³ Center for Astronomy and Astrophysics, Technical University Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
¹⁴ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
¹⁵ Deptartamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
¹⁶ ESTEC, European Space Agency, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹⁷ Admatis, Miskolc, Hungary
¹⁸ Depto. de Astrofísica, Centro de Astrobiología (CSIC-INTA), ESAC campus, 28692 Villanueva de la Cãda (Madrid), Spain
¹⁹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
²⁰ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
²¹ INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
²² Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
²³ Institut de Physique du Globe de Paris (IPGP), 1 rue Jussieu, 75005 Paris, France
²⁴ Lund Observatory, Department of Astronomy & Theoretical Physics, Lund University, Box 43, Lund 22100, Sweden
²⁵ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
²⁶ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
²⁷ INAF, Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
²⁸ Division Technique INSU, BP 330, 83507 La Seyne cedex, France
²⁹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, 1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
³⁰ Institut d’astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis blvd. Arago, 75014 Paris, France
³¹ University of Vienna, Department of Astrophysics, Türkenschanzstr. 17, 1180 Vienna, Austria
³² IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL Univ., Sorbonne Univ., 77 av. Denfert-Rochereau, 75014 Paris, France
³³ INAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
³⁴ Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstr. 2, 12489 Berlin, Germany
³⁵ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Universita’ degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
³⁶ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
³⁷ Institut für Geologische Wissenschaften, Freie Universität Berlin, 12249 Berlin, Germany
³⁸ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, C/CanMagrans s/n, 08193 Bellaterra, Spain
³⁹ Institut d’Estudis Espacials de Catalunya (IEEC), Gran Capità 2-4, 08034 Barcelona, Spain
⁴⁰ ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, Szombathely, Hungary
⁴¹ MTA-ELTE Exoplanet Research Group, 9700 Szombathely, Szent Imre h. u. 112, Hungary
⁴² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

Received: 16 June 2020
Accepted: 17 September 2020

Abstract

The CHEOPS space mission dedicated to exoplanet follow-up was launched in December 2019, equipped with the capacity to perform photometric measurements at the 20 ppm level. As CHEOPS carries out its observations in a broad optical passband, it can provide insights into the reflected light from exoplanets and constrain the short-wavelength thermal emission for the hottest of planets by observing occultations and phase curves. Here, we report the first CHEOPS observation of an occultation, namely, that of the hot Jupiter WASP-189 b, a M_P ≈ 2M_J planet orbiting an A-type star. We detected the occultation of WASP-189 b at high significance in individual measurements and derived an occultation depth of dF = 87.9 ± 4.3 ppm based on four occultations. We compared these measurements to model predictions and we find that they are consistent with an unreflective atmosphere heated to a temperature of 3435 ± 27 K, when assuming inefficient heat redistribution. Furthermore, we present two transits of WASP-189 b observed by CHEOPS. These transits have an asymmetric shape that we attribute to gravity darkening of the host star caused by its high rotation rate. We used these measurements to refine the planetary parameters, finding a ~25% deeper transit compared to the discovery paper and updating the radius of WASP-189 b to 1.619 ± 0.021R_J. We further measured the projected orbital obliquity to be λ = 86.4_−4.4^+2.9°, a value that is in good agreement with a previous measurement from spectroscopic observations, and derived a true obliquity of Ψ = 85.4 ± 4.3°. Finally, we provide reference values for the photometric precision attained by the CHEOPS satellite: for the V = 6.6 mag star, and using a 1-h binning, we obtain a residual RMS between 10 and 17 ppm on the individual light curves, and 5.7 ppm when combining the four visits.