The transiting system GJ1214: high-precision defocused transit observations^⋆, and a search for evidence of transit timing variation^⋆⋆

¹ Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, 2100 Copenhagen Ø, Denmark
e-mail: harpsoe@nbi.ku.dk
² Centre for Star and Planet Formation, Natural History Museum of Denmark, Øster Voldgade 5, 1350 Copenhagen, Denmark
³ Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, 305-348 Daejeon, Republic of Korea
⁴ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
⁵ SUPA, University of St Andrews, School of Physics & Astronomy, North Haugh, St Andrews, KY16 9SS UK
⁶ Department of Physics, Sharif University of Technology, PO Box 11155-9161, Tehran, Iran
⁷ Max-Planck-Institute for Solar System Research, Max-Planck Str. 2, 37191 Katlenburg-Lindau, Germany
⁸ Qatar Foundation, Doha, Qatar
⁹ Dipartimento di Fisica “E. R. Caianiello”, Università di Salerno, via Ponte Don Melillo, 84084 Fisciano (SA), Italy
¹⁰ HE Space Operations GmbH, Flughafenallee 24, 28199 Bremen, Germany
¹¹ Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli, Italy
¹² Istituto Internazionale per gli Alti Studi Scientifici (IIASS), 84019 Vietri Sul Mare (SA), Italy
¹³ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹⁴ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
¹⁵ Institut d’Astrophysique et de Géophysique, Université de Liège, 4000 Liège, Belgium
¹⁶ Astronomisches Rechen-Institut, Zentrum für Astronomie, Universität Heidelberg, Mönchhofstraße 12-14, 69120 Heidelberg, Germany
¹⁷ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁸ Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
¹⁹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²⁰ Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
²¹ National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, 650011 Kunming, PR China
²² Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo ON, N2L 2Y5, Canada
²³ Southwest Research Institute, Department of Space Studies, 1050 Walnut St., Suite 400, Boulder, CO 80302, USA

Received: 12 July 2012
Accepted: 5 October 2012

Abstract

Aims. We present 11 high-precision photometric transitobservations of the transiting super-Earth planet GJ 1214 b. Combining these data with observations from other authors, we investigate the ephemeris for possible signs of transit timing variations (TTVs) using a Bayesian approach.

Methods. The observations were obtained using telescope-defocusing techniques, and achieve a high precision with random errors in the photometry as low as 1 mmag per point. To investigate the possibility of TTVs in the light curve, we calculate the overall probability of a TTV signal using Bayesian methods.

Results. The observations are used to determine the photometric parameters and the physical properties of the GJ 1214 system. Our results are in good agreement with published values. Individual times of mid-transit are measured with uncertainties as low as 10 s, allowing us to reduce the uncertainty in the orbital period by a factor of two.

Conclusions. A Bayesian analysis reveals that it is highly improbable that the observed transit times is explained by TTV caused by a planet in the nominal habitable zone, when compared with the simpler alternative of a linear ephemeris.