WASP-54b, WASP-56b, and WASP-57b: Three new sub-Jupiter mass planets from SuperWASP^⋆,⋆⋆

¹ Department of PhysicsUniversity of Warwick, Coventry, CV4 7AL UK
e-mail: f.faedi@warwick.ac.uk
² Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN, UK
³ Aix Marseille Universit, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁴ School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, UK
⁵ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
⁶ Université de Liège, Allée du 6 août 17, Sart Tilman, Liège 1, Belgium
⁷ Physics and Astronomy Department, Vanderbilt University, Nashville, Tennessee, USA
⁸ Institut d’Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, France
⁹ Observatoire de Haute-Provence, CNRS/OAMP, 04870 St Michel l’Observatoire, France
¹⁰ Observatoire astronomique de l’Université de Genève, 51 ch. des Maillettes, 1290 Sauverny, Switzerland
¹¹ Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
¹² Qatar Foundation, PO Box 5825, Doha, Qatar
¹³ Department of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
¹⁴ Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hgel 71, 53121 Bonn, Germany
¹⁵ Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de Palma, Spain

Received: 8 October 2012
Accepted: 23 December 2012

Abstract

We present three newly discovered sub-Jupiter mass planets from the SuperWASP survey: WASP-54b is a heavily bloated planet of mass 0.636^+0.025_-0.024M_J and radius 1.653^+0.090_-0.083R_J. It orbits a F9 star, evolving off the main sequence, every 3.69 days. Our MCMC fit of the system yields a slightly eccentric orbit (e = 0.067^+0.033_-0.025) for WASP-54b. We investigated further the veracity of our detection of the eccentric orbit for WASP-54b, and we find that it could be real. However, given the brightness of WASP-54 V = 10.42 mag, we encourage observations of a secondary eclipse to draw robust conclusions on both the orbital eccentricity and the thermal structure of the planet. WASP-56b and WASP-57b have masses of 0.571^+0.034_-0.035M_J and 0.672^+0.049_-0.046M_J, respectively; and radii of 1.092^+0.035_-0.033R_J for WASP-56b and 0.916^+0.017_-0.014R_J for WASP-57b. They orbit main sequence stars of spectral type G6 every 4.67 and 2.84 days, respectively. WASP-56b and WASP-57b show no radius anomaly and a high density possibly implying a large core of heavy elements; possibly as high as ~50 M_⊕ in the case of WASP-57b. However,the composition of the deep interior of exoplanets remains still undetermined. Thus, more exoplanet discoveries such as the ones presented in this paper, are needed to understand and constrain giant planets’ physical properties.