The TRAPPIST survey of southern transiting planets

I. Thirty eclipses of the ultra-short period planet WASP-43 b^{⋆,⋆⋆,⋆⋆⋆}

¹ Université de Liège, Allée du 6 août 17, Sart Tilman, Liège 1, Belgium
e-mail: michael.gillon@ulg.ac.be
² Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
³ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
⁴ Department of Earth, Atmospheric and Planetary Sciences, Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA
⁵ European Southern Observatory, Alonso de Cordova 3107, 19001 Casilla, Santiago, Chile
⁶ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
⁷ School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife, KY16 9SS, UK
⁸ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA

Received: 13 January 2012
Accepted: 26 March 2012

Abstract

We present twenty-three transit light curves and seven occultation light curves for the ultra-short period planet WASP-43 b, in addition to eight new measurements of the radial velocity of the star. Thanks to this extensive data set, we improve significantly the parameters of the system. Notably, the largely improved precision on the stellar density (2.41 ± 0.08 ρ_⊙) combined with constraining the age to be younger than a Hubble time allows us to break the degeneracy of the stellar solution mentioned in the discovery paper. The resulting stellar mass and size are 0.717 ± 0.025 M_⊙ and 0.667 ± 0.011 R_⊙. Our deduced physical parameters for the planet are 2.034 ± 0.052 M_Jup and 1.036 ± 0.019 R_Jup. Taking into account its level of irradiation, the high density of the planet favors an old age and a massive core. Our deduced orbital eccentricity, 0.0035_-0.0025^+0.0060, is consistent with a fully circularized orbit. We detect the emission of the planet at 2.09 μm at better than 11-σ, the deduced occultation depth being 1560 ± 140 ppm. Our detection of the occultation at 1.19 μm is marginal (790 ± 320 ppm) and more observations are needed to confirm it. We place a 3-σ upper limit of 850 ppm on the depth of the occultation at ~0.9 μm. Together, these results strongly favor a poor redistribution of the heat to the night-side of the planet, and marginally favor a model with no day-side temperature inversion.