Revisiting TrES-5 b: departure from a linear ephemeris instead of short-period transit timing variation

Aims. The orbital motion of the transiting hot Jupiter TrES-5 b was reported to be perturbed by a planetary companion on a nearby orbit. Such compact systems do not frequently occur in nature, and investigating their orbital architecture could shed some light on the formation processes of hot Jupiters. Methods. We acquired 15 new precise photometric time-series for 12 transits of TrES-5 b between June 2019 and October 2020 using 0.9-2.0 m telescopes. The method of precise transit timing was employed to verify the deviation of the planet from the Keplerian motion. Results. Although our results show no detectable short-time variation in the orbital period of TrES-5 b and the existence of the additional nearby planet is not confirmed, the new transits were observed about two minutes earlier than expected. We conclude that the orbital period of the planet could vary on a long timescale. We found that the most likely explanation of the observations is the line-of-sight acceleration of the system's barycentre caused by the orbital motion induced by a massive, wide-orbiting companion.