Multi-site campaign for transit timing variations of WASP-12 b: possible detection of a long-period signal of planetary origin^{⋆,⋆⋆,⋆⋆⋆}

¹ Toruń Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87100 Toruń, Poland
e-mail: gm@astri.umk.pl
² Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko Chausse Blvd., 1784 Sofia, Bulgaria
³ Astrophysikalisches Institut und Universitäts-Sternwarte, Schillergässchen 2–3, 07745 Jena, Germany
⁴ Michael Adrian Observatorium, Astronomie Stiftung Trebur, Trebur, Germany
⁵ University of Applied Sciences, Technische Hochschule Mittelhessen, Friedberg, Germany
⁶ Advanced Astronomy and Space Science Division, Korea Astronomy and Space Science Institute, Daejeon 305-348, Republic of Korea
⁷ Chungbuk National University Observatory, Cheongju 365-863, Republic of Korea
⁸ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁹ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
¹⁰ INAF – Astronomical Observatory of Capodimonte Salita Moiariello 16, 80131 Napoli, Italy
¹¹ Societá Astronomica Lunae, Castelnuovo Magra, 19030 La Spezia, Italy
¹² Unione Astrofili Italiani, Sezione Stelle Variabili – GRAV, Italy
¹³ Institute of Astronomy, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
¹⁴ Joint ALMA Observatory, Alonso de C’rdova 3107, Vitacura, Santiago, Chile
¹⁵ National Astronomical Observatory of Japan, 2-21-1, Osawa, Miaka, Tokyo, 181-8588, Japan
¹⁶ MTA CSFK, Konkoly Observatory, Konkoly-Thege Mikloś út 15−17, 1121 Budapest, Hungary
¹⁷ ELTE Gothard–Lendület Research Group, 9700 Szombathely, Hungary
¹⁸ Dept. of Exp. Physics & Astronomical Observatory, University of Szeged, 6720 Szeged, Hungary
¹⁹ Department of Physics, Eötvös University, Pázmány Péter Sétány 1/A, 1117 Budapest, Hungary
²⁰ Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranská Lomnica, Slovakia
²¹ Aryabhatta Research Institute of Observational Sciences(ARIES), Manora Peak, Nainital 263129, India
²² Institute of Astronomy, National Central University, 300 Jhongda Rd., Jhongli 32001, Taiwan

Received: 15 November 2012
Accepted: 18 January 2013

Abstract

Aims. The transiting planet WASP-12 b was identified as a potential target for transit-timing studies because a departure from a linear ephemeris has been reported in the literature. Such deviations could be caused by an additional planet in the system. We attempt to confirm the claimed variations in transit timing and interpret their origin.

Methods. We organised a multi-site campaign to observe transits by WASP-12 b in three observing seasons, using 0.5–2.6-metre telescopes.

Results. We obtained 61 transit light curves, many of them with sub-millimagnitude precision. The simultaneous analysis of the best-quality datasets allowed us to obtain refined system parameters, which agree with values reported in previous studies. The residuals versus a linear ephemeris reveal a possible periodic signal that may be approximated by a sinusoid with an amplitude of 0.00068 ± 0.00013 d and period of 500 ± 20 orbital periods of WASP-12 b. The joint analysis of timing data and published radial velocity measurements results in a two-planet model that explains observations better than do single-planet scenarios. We hypothesise that WASP-12 b might not be the only planet in the system, and there might be the additional 0.1 M_Jup body on a 3.6-d eccentric orbit. A dynamical analysis indicates that the proposed two-planet system is stable on long timescales.