Transiting exoplanets from the CoRoT space mission

XXV. CoRoT-27b: a massive and dense planet on a short-period orbit^⋆

¹ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife Spain
e-mail: hannu.parviainen@astro.ox.ac.uk
² Dept. Astrofísica, Universidad de La Laguna (ULL), 38206, La Laguna Tenerife, Spain
³ Department of Physics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁴ INAF-Catania Astrophysical Observatory, via S. Sofia 78, 95123 Catania, Italy
⁵ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁶ IAG, Universidade de São Paulo, 05508-090 Säo Paulo, Brazil
⁷ LESIA, UMR 8109 CNRS, Observatoire de Paris, UVSQ, Université Paris-Diderot, 5 place J. Janssen, 92195 Meudon Cedex, France
⁸ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
⁹ Thüringer Landessternwarte, CoRoT (DLR), Sternwarte 5, Tautenburg, 07778 Tautenburg, Germany
¹⁰ NASA Ames Research Center, MS 244-30, PO Box 1, 94035-0001 Moffett Field, USA
¹¹ Research and Scientific Support Department, ESTEC/ESA, PO Box 299, 2200 AG Noordwijk, The Netherlands
¹² Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
¹³ Rheinisches Institut für Umweltforschung an der Universität zu Köln, Aachener Strasse 209, 50931 Kölen, Germany
¹⁴ Institut d’Astrophysique Spatiale, Université Paris XI, 91405 Orsay, France
¹⁵ Observatoire de Haute-Provence, Saint-Michel-l’Observatoire 04670, France
¹⁶ Institut d’Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
¹⁷ University of Vienna, Institute of Astronomy, Türkenschanzstr. 17, 1180 Vienna, Austria
¹⁸ Observatoire de la Côte d’Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 4, France
¹⁹ School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
²⁰ Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
²¹ Centro de Astrofísica, Universidade do Porto, rua das Estrelas, 4150-762 Porto, Portugal
²² LUTH, Observatoire de Paris, CNRS, Université Paris Diderot; 5 place Jules Janssen, 92195 Meudon, France

Received: 14 November 2013
Accepted: 31 December 2013

Abstract

Aims. We report the discovery of a massive and dense transiting planet CoRoT-27b on a 3.58-day orbit around a 4.2 Gyr-old G2 star. The planet candidate was identified from the CoRoT photometry, and was confirmed as a planet with ground-based spectroscopy.

Methods. The confirmation of the planet candidate is based on radial velocity observations combined with imaging to rule out blends. The characterisation of the planet and its host star was carried out using a Bayesian approach where all the data (CoRoT photometry, radial velocities, and spectroscopic characterisation of the star) are used jointly. The Bayesian analysis included a study whether the assumption of white normally distributed noise holds for the CoRoT photometry and whether the use of a non-normal noise distribution offers advantages in parameter estimation and model selection.

Results. CoRoT-27b has a mass of 10.39 ± 0.55M_Jup, a radius of 1.01 ± 0.04R_Jup, a mean density of $\mathrm{12.}{\mathrm{6}}_{-1.67}^{\mathrm{+}\mathrm{1.92}}$g   cm^-3, and an effective temperature of 1500 ± 130 K. The planet orbits around its host star, a 4.2 Gyr-old G2-star with a mass M_⋆ = 1.06M_⊙ and a radius R_⋆ = 1.05R_⊙, on a 0.048 ± 0.007 AU orbit of 3.58 days. The radial velocity observations allow us to exclude highly eccentric orbits, namely, e < 0.065 with 99% confidence. Given its high mass and density, theoretical modelling of CoRoT-27b is demanding. We identify two solutions with heavy element mass fractions of 0.11 ± 0.08M⊕ and 0.07 ± 0.06M_⊕, but even solutions void of heavy elements cannot be excluded. We carry out a secondary eclipse search from the CoRoT photometry using a method based on Bayesian model selection, but conclude that the noise level is too high to detect eclipses shallower than 9% of the transit depth. Using a non-normal noise model was shown not to affect the parameter estimation results, but led to significant improvement in the sensitivity of the model selection process.