Discovery and characterization of the exoplanets WASP-148b and c

A transiting system with two interacting giant planets^★

¹ Institut d’astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
e-mail: hebrard@iap.fr
² Observatoire de Haute-Provence, CNRS, Université d’Aix-Marseille, 04870 Saint-Michel-l’Observatoire, France
³ International Center for Advanced Studies (ICAS) and ICIFI (CONICET), ECyT-UNSAM, Campus Miguelete, 25 de Mayo y Francia, (1650) Buenos Aires, Argentina
⁴ Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina
⁵ CONICET – Universidad de Buenos Aires. Instituto de Astronomía y Física del Espacio (IAFE), Buenos Aires, Argentina
⁶ CFisUC, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal
⁷ IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL University, Sorbonne Univ., 77 av. Denfert-Rochereau, 75014 Paris, France
⁸ School of Physics and Astronomy, Physical Science Building, North Haugh, St Andrews, UK
⁹ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹⁰ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹¹ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹² Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
¹³ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁴ Laboratoire d’Astrophysique de Marseille, Univ. de Provence, UMR6110 CNRS, 38 r. F. Joliot Curie, 13388 Marseille, cedex 13, France
¹⁵ INAF, Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025, Pino Torinese, Italy
¹⁶ Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
¹⁷ Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Obs. of Athens, 15236 Penteli, Greece
¹⁸ School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
¹⁹ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
²⁰ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 92195 Meudon, France
²¹ Center for Astronomy and Astrophysics, Technical University Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
²² Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
²³ Deptartamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
²⁴ Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK
²⁵ Observatoire Hubert-Reeves, 07320 Mars, France

Received: 29 April 2020
Accepted: 16 June 2020

Abstract

We present the discovery and characterization of WASP-148, a new extrasolar system that includes at least two giant planets. The host star is a slowly rotating inactive late-G dwarf with a V = 12 magnitude. The planet WASP-148b is a hot Jupiter of 0.72 R_Jup and 0.29 M_Jup that transits its host with an orbital period of 8.80 days. We found the planetary candidate with the SuperWASP photometric survey, then characterized it with the SOPHIE spectrograph. Our radial velocity measurements subsequently revealed a second planet in the system, WASP-148c, with an orbital period of 34.5 days and a minimum mass of 0.40 M_Jup. No transits of this outer planet were detected. The orbits of both planets are eccentric and fall near the 4:1 mean-motion resonances. This configuration is stable on long timescales, but induces dynamical interactions so that the orbits differ slightly from purely Keplerian orbits. In particular, WASP-148b shows transit-timing variations of typically 15 min, making it the first interacting system with transit-timing variations that is detected on ground-based light curves. We establish that the mutual inclination of the orbital plane of the two planets cannot be higher than 35°, and the true mass of WASP-148c is below 0.60 M_Jup. We present photometric and spectroscopic observations of this system that cover a time span of ten years. We also provide their Keplerian and Newtonian analyses; these analyses should be significantly improved through future TESS observations.