WASP-78b and WASP-79b: two highly-bloated hot Jupiter-mass exoplanets orbiting F-type stars in Eridanus^⋆,⋆⋆

¹ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
e-mail: b.smalley@keele.ac.uk
² SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife, KY16 9SS, UK
³ Université de Liège, Allée du 6 août 17, Sart Tilman, Liège 1, Belgium
⁴ Observatoire de Genève, Université de Genève, Chemin des maillettes 51, 1290 Sauverny, Switzerland
⁵ Astrophysics Research Centre, School of Mathematics & Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN, UK
⁶ Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK

Received: 1 June 2012
Accepted: 28 September 2012

Abstract

We report the discovery of WASP-78b and WASP-79b, two highly-bloated Jupiter-mass exoplanets orbiting F-type host stars. WASP-78b orbits its V = 12.0 host star (TYC 5889-271-1) every 2.175 days and WASP-79b orbits its V = 10.1 host star (CD-30 1812) every 3.662 days. Planetary parameters have been determined using a simultaneous fit to WASP and TRAPPIST transit photometry and CORALIE radial-velocity measurements. For WASP-78b a planetary mass of 0.89  ±  0.08 M_Jup and a radius of 1.70  ±  0.11 R_Jup is found. The planetary equilibrium temperature of T_P = 2350 ± 80 K for WASP-78b makes it one of the hottest of the currently known exoplanets. WASP-79b its found to have a planetary mass of 0.90  ±  0.08 M_Jup, but with a somewhat uncertain radius due to lack of sufficient TRAPPIST photometry. The planetary radius is at least 1.70  ±  0.11 R_Jup, but could be as large as 2.09  ±  0.14 R_Jup, which would make WASP-79b the largest known exoplanet.