Photodynamical analysis of the nearly resonant planetary system WASP-148

Accurate transit-timing variations and mutual orbital inclination

¹ Observatoire de Genève, Département d’Astronomie, Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
e-mail: Jose-Manuel.Almenara-Villa@univ-grenoble-alpes.fr
³ Institut d’astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁴ Observatoire de Haute-Provence, 04670 Saint Michel l’Observatoire, France
⁵ International Center for Advanced Studies (ICAS) and ICIFI (CON-ICET), ECyT-UNSAM, Campus Miguelete, 25 de Mayo y Francia, (1650) Buenos Aires, Argentina
⁶ IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL University, Sorbonne Univ., 77 av. Denfert-Rochereau, 75014 Paris, France
⁷ CFisUC, Departamento de Física, Universidade de Coimbra, 3004–516 Coimbra, Portugal
⁸ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁹ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹⁰ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
¹¹ Laboratoire d’Astrophysique de Marseille, Univ. de Provence, UMR6110 CNRS, 38 r. F. Joliot Curie, 13388 Marseille cedex 13, France
¹² Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía 3, 18008 Granada, Spain
¹³ School of Physics and Astronomy, Physical Science Building, North Haugh, St Andrews, UK
¹⁴ NASA Ames Research Center, Moffett Field, CA 94035 USA
¹⁵ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 92195 Meudon, France
¹⁶ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87–100 Toruń, Poland
¹⁷ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
¹⁸ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
¹⁹ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
²⁰ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139 USA
²¹ Observatoire Hubert-Reeves, 07320 Mars, France
²² Department of Astrophysical Sciences, Princeton University, NJ 08544 USA

Received: 21 December 2021
Accepted: 6 April 2022

Abstract

WASP-148 is a recently announced extra-solar system harbouring at least two giant planets. The inner planet transits its host star. The planets travel on eccentric orbits and are near the 4:1 mean-motion resonance, which implies significant mutual gravitational interactions. In particular, this causes transit-timing variations of a few minutes, which were detected based on ground-based photometry. This made WASP-148 one of the few cases where such a phenomenon was detected without space-based photometry. Here, we present a self-consistent model of WASP-148 that takes into account the gravitational interactions between all known bodies in the system. Our analysis simultaneously fits the available radial velocities and transit light curves. In particular, we used the photometry secured by the Transiting Exoplanet Survey Satellite (TESS) and made public after the WASP-148 discovery announcement. The TESS data confirm the transit-timing variations, but only in combination with previously measured transit times. The system parameters we derived agree with those previously reported and have a significantly improved precision, including the mass of the non-transiting planet. We found a significant mutual inclination between the orbital planes of the two planets: I = 41.0^+6.2°_-7.6 based on the modelling of the observations, although we found I = 20.8 ± 4.6° when we imposed a constraint on the model enforcing long-term dynamical stability. When a third planet was added to the model – based on a candidate signal in the radial velocity – the mutual inclination between planets b and c changed significantly allowing solutions closer to coplanar. We conclude that more data are needed to establish the true architecture of the system. If the significant mutual inclination is confirmed, WASP-148 would become one of the only few candidate non-coplanar planetary systems. We discuss possible origins for this misalignment.