Physical properties of the WASP-67 planetary system from multi-colour photometry^⋆,⋆⋆

¹ Max-Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: mancini@mpia.de
² Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
³ International Institute for Advanced Scientific Studies (IIASS), 84019 Vietri Sul Mare (SA), Italy
⁴ Department of Physics, University of Salerno, Via Giovanni Paolo II, 84084 Fisciano, Italy
⁵ SUPA, University of St Andrews, School of Physics & Astronomy, North Haugh, St Andrews, KY16 9SS, UK
⁶ Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, 2100 Copenhagen Ø, Denmark
⁷ Centre for Star and Planet Formation, Geological Museum, Øster Voldgade 5-7, 1350 Copenhagen, Denmark
⁸ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
⁹ Astrophysics Group, University of Exeter, Stocker Road, EX4 4QL, Exeter, UK
¹⁰ Qatar Foundation, PO Box 5825, Doha, Qatar
¹¹ Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, 80126 Napoli, Italy
¹² Qatar Environment and Energy Research Institute, Qatar Foundation, Tornado Tower, Floor 19, PO Box 5825, Doha, Qatar
¹³ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
¹⁴ Yunnan Observatories, Chinese Academy of Sciences, 650011 Kunming, PR China
¹⁵ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, 650011 Kunming, PR China
¹⁶ Korea Astronomy and Space Science Institute, Daejeon 305-348, Republic of Korea
¹⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁸ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
¹⁹ Department of Physics, Sharif University of Technology, PO Box 11155-9161 Tehran, Iran
²⁰ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
²¹ Las Cumbres Observatory Global Telescope Network, 6740B Cortona Drive, Goleta, CA 93117, USA
²² Institut d’Astrophysique et de Géophysique, Université de Liège, 4000 Liège, Belgium
²³ School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, UK

Received: 30 April 2014
Accepted: 28 June 2014

Abstract

Context. The extrasolar planet WASP-67 b is the first hot Jupiter definitively known to undergo only partial eclipses. The lack of the second and third contact points in this planetary system makes it difficult to obtain accurate measurements of its physical parameters.

Aims. By using new high-precision photometric data, we confirm that WASP-67 b shows grazing eclipses and compute accurate estimates of the physical properties of the planet and its parent star.

Methods. We present high-quality, multi-colour, broad-band photometric observations comprising five light curves covering two transit events, obtained using two medium-class telescopes and the telescope-defocusing technique. One transit was observed through a Bessel-R filter and the other simultaneously through filters similar to Sloan g′r′i′z′. We modelled these data using jktebop. The physical parameters of the system were obtained from the analysis of these light curves and from published spectroscopic measurements.

Results. All five of our light curves satisfy the criterion for being grazing eclipses. We revise the physical parameters of the whole WASP-67 system and, in particular, significantly improve the measurements of the planet’s radius (R_b = 1.091 ± 0.046 R_Jup) and density (ρ_b = 0.292 ± 0.036 ρ_Jup), as compared to the values in the discovery paper (R_b = 1.4 _-0.2^+0.3 R_Jup and ρ_b = 0.16 ± 0.08 ρ_Jup). The transit ephemeris was also substantially refined. We investigated the variation of the planet’s radius as a function of the wavelength, using the simultaneous multi-band data, finding that our measurements are consistent with a flat spectrum to within the experimental uncertainties.