Departure from the constant-period ephemeris for the transiting exoplanet WASP-12 b^⋆,⋆⋆

¹ Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland
e-mail: gmac@umk.pl
² Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko Chausse Blvd., 1784 Sofia, Bulgaria
³ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía 3, 18008 Granada, Spain
⁴ Instituto de Astrofísica de Canarias, C/ vía Láctea, s/n, 38205 La Laguna, Tenerife, Spain
⁵ Departamento de Astrofísica, Universidad de La Laguna, Av. Astrofísico Francisco Sánchez, s/n, 38206 La Laguna, Tenerife, Spain
⁶ Michael Adrian Observatorium, Astronomie Stiftung Trebur, 65428 Trebur, Germany
⁷ University of Applied Sciences, Technische Hochschule Mittelhessen, 61169 Friedberg, Germany
⁸ Korea Astronomy & Space Science Institute (KASI), 305-348 Daejeon, Republic of Korea
⁹ Stellar Astrophysics Centre, Institut for Fysik og Astronomi, Åarhus Universitet, Ny Munkegade 120, 8000 Åarhus C, Denmark
¹⁰ Department of Physics, Shumen University, 9700 Shumen, Bulgaria

Received: 15 February 2016
Accepted: 27 February 2016

Abstract

Aims. Most hot Jupiters are expected to spiral in toward their host stars because the angular momentum of the orbital motion is transferred to the stellar spin. Their orbits can also precess as a result of planet-star interactions. Calculations show that both effects might be detected for the very-hot exoplanet WASP-12 b using the method of precise transit-timing over a time span of about 10 yr.

Methods. We acquired new precise light curves for 29 transits of WASP-12 b, spannning four observing seasons from November 2012 to February 2016. New mid-transit times, together with those from the literature, were used to refine the transit ephemeris and analyze the timing residuals.

Results. We find that the transit times of WASP-12 b do not follow a linear ephemeris with a 5σ confidence level. They may be approximated with a quadratic ephemeris that gives a change rate in the orbital period of (−2.56 ± 0.40) × 10^-2 s yr^-1. The tidal quality parameter of the host star was found to be equal to 2.5 × 10⁵, which is similar to theoretical predictions for Sun-like stars. We also considered a model in which the observed timing residuals are interpreted as a result of the apsidal precession. We find, however, that this model is statistically less probable than the orbital decay.