WASP-34b: a near-grazing transiting sub-Jupiter-mass exoplanet in a hierarchical triple system^⋆

B. Smalley¹, D. R. Anderson¹, A. Collier Cameron², C. Hellier¹, M. Lendl³, P. F. L. Maxted¹, D. Queloz³, A. H. M. J. Triaud³, R. G. West⁴, S. J. Bentley¹, B. Enoch², M. Gillon^5,3, T. A. Lister⁶, F. Pepe³, D. Pollacco⁷, D. Segransan³, A. M. S. Smith¹, J. Southworth¹, S. Udry³, P. J. Wheatley⁸, P. L. Wood¹ and J. Bento⁸

¹ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
e-mail: bs@astro.keele.ac.uk
² SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife, KY16 9SS, UK
³ Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
⁴ Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
⁵ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août, 17, Bât. B5C, Liège 1, Belgium
⁶ Las Cumbres Observatory, 6740 Cortona Dr. Suite 102, Santa Barbara, CA 93117, USA
⁷ Astrophysics Research Centre, School of Mathematics & Physics, Queen’s University, University Road, Belfast, BT7 1NN, UK
⁸ Department of Physics, University of Warwick, Coventry CV4 7AL, UK

Received: 25 October 2010
Accepted: 9 December 2010

Abstract

We report the discovery of WASP-34b, a sub-Jupiter-mass exoplanet transiting its 10.4-magnitude solar-type host star (1SWASP J110135.89-235138.4; TYC 6636-540-1) every 4.3177 days in a slightly eccentric orbit (e = 0.038 ± 0.012). We find a planetary mass of 0.59 ± 0.01 M_Jup and radius of  R_Jup. There is a linear trend in the radial velocities of 55 ± 4 m s^-1 y^-1 indicating the presence of a long-period third body in the system with a mass  ≳0.45 M_Jup at a distance of  ≳1.2 AU from the host star. This third-body is either a low-mass star, a white dwarf, or another planet. The transit depth ((R_P/R_∗)² = 0.0126) and high impact parameter (b = 0.90) suggest that this could be the first known transiting exoplanet expected to undergo grazing transits, but with a confidence of only  ~80%.