From dense hot Jupiter to low-density Neptune: The discovery of WASP-127b, WASP-136b, and WASP-138b^⋆

¹ University of Warwick, Department of Physics, Gibbet Hill Road, Coventry, CV4 7AL, UK
e-mail: w.f.lam@warwick.ac.uk
² Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
³ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Aout, 17 Bât. B5C, Liège 1, Belgium
⁴ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁵ Observatoire de Haute-Provence, Université d’Aix-Marseille & CNRS, 04870 Saint-Michel-l’ Observatoire, France
⁶ Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
⁷ Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
⁸ Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg, Germany
⁹ Centre for Planetary Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada
¹⁰ Department of Astronomy & Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada
¹¹ Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK
¹² SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife KY16 9SS, UK
¹³ ARC, School of Mathematics & Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN, UK
¹⁴ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁵ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
¹⁶ INAF–Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
¹⁷ Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, 15236 Penteli, Greece
¹⁸ Instituto de Astrofisica de Canarias, via Lactea sn, 38200 La Laguna, Tenerife, Spain
¹⁹ Cavendish Laboratory, J J Thomson Avenue, Cambridge, CB3 0HE, UK

Received: 22 July 2016
Accepted: 20 October 2016

Abstract

We report three newly discovered exoplanets from the SuperWASP survey. WASP-127b is a heavily inflated super-Neptune of mass 0.18±0.02 M_J and radius 1.37±0.04 R_J. This is one of the least massive planets discovered by the WASP project. It orbits a bright host star (V_mag = 10.16) of spectral type G5 with a period of 4.17 days. WASP-127b is a low-density planet that has an extended atmosphere with a scale height of 2500 ± 400 km, making it an ideal candidate for transmission spectroscopy. WASP-136b and WASP-138b are both hot Jupiters with mass and radii of 1.51 ± 0.08 M_J and 1.38 ± 0.16 R_J, and 1.22 ± 0.08 M_J and 1.09 ± 0.05 R_J, respectively. WASP-136b is in a 5.22-day orbit around an F9 subgiant star with a mass of 1.41 ± 0.07 M_⊙ and a radius of 2.21 ± 0.22 R_⊙. The discovery of WASP-136b could help constrain the characteristics of the giant planet population around evolved stars. WASP-138b orbits an F7 star with a period of 3.63 days. Its radius agrees with theoretical values from standard models, suggesting the presence of a heavy element core with a mass of ~ 10 M_⊕. The discovery of these new planets helps in exploring the diverse compositional range of short-period planets, and will aid our understanding of the physical characteristics of both gas giants and low-density planets.