The discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert^★

¹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
e-mail: olivier.demangeon@astro.up.pt
² University of Warwick, Department of Physics, Gibbet Hill Road, Coventry CV4 7AL, UK
³ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁴ Observatoire de Haute-Provence, Université d'Aix-Marseille & CNRS, 04870 Saint Michel l'Observatoire, France
⁵ Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
⁶ Astrophysics Research Centre, Queen's University Belfast, University Road, Belfast BT7 1NN, UK
⁷ Centre for Exoplanet Science, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, UK
⁸ INAF–Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
⁹ INAF–Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
¹⁰ Cavendish Laboratory, JJ Thompson Avenue, CB3 0HE Cambridge, UK
¹¹ Institute of Astronomy, Madingley Road, CB3 0HA Cambridge, UK
¹² Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
¹³ School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
¹⁴ Instituto de Astrosfísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
¹⁵ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La laguna, Tenerife, Spain
¹⁶ Max Planck Institue for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁷ School of Physical Sciences, The Open University, Milton Keynes MK7 6 AA, UK
¹⁸ Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, 15236 Penteli, Greece
¹⁹ Department of Physics, University of Rome Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
²⁰ Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
²¹ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 17, Bat. B5C, 4000 Liège, Belgium

Received: 7 August 2017
Accepted: 16 October 2017

Abstract

To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets' mass and radius with a good precision (≲10%) is essential. To achieve this purpose the discovery of transiting exoplanets around bright stars is of prime interest. In this paper, we report the discovery of three transiting exoplanets by the SuperWASP survey and the SOPHIE spectrograph with mass and radius determined with a precision better than 15%. WASP-151b and WASP-153b are two hot Saturns with masses, radii, densities and equilibrium temperatures of 0.31_−0.03^+0.04 M_J, 1.13_−0.03^+0.03 R_J, 0.22_−0.02^+0.03 ρ_J and 1290₋₁₀⁺²⁰ K, and 0.39_−0.02^+0.02 M_J, 1.55_−0.08^+0.10 R_J, 0.11_−0.02^+0.02 ρ_J and 1700_−0.40^+0.40 K, respectively. Their host stars are early G type stars (with mag V ~ 13) and their orbital periods are 4.53 and 3.33 days, respectively. WASP-156b is a super-Neptune orbiting a K type star (mag V = 11.6). It has a mass of 0.128_−0.009^+0.010 M_J, a radius of 0.51_−0.02^+0.02 R_J, a density of 1.0_−0.1^+0.1 ρ_J, an equilibrium temperature of 970₋₂₀⁺³⁰ K and an orbital period of 3.83 days. The radius of WASP-151b appears to be only slightly inflated, while WASP-153b presents a significant radius anomaly compared to a recently published model. WASP-156b, being one of the few well characterized super-Neptunes, will help to constrain the still debated formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms an already observed tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages. We propose that high eccentricity migration could partially explain this behavior for stars hosting a short period planet. Finally, these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert. Their characteristics support that the ultra-violet irradiation plays an important role in this depletion of planets observed in the exoplanet population.