A multi-colour phase-polarization curve of asteroid (3200) Phaethon has been obtained during the December 2017 apparition by merging measurements taken at the observing station of Calern (France) and at the Rhozen observatory (Bulgaria). All the observations were obtained in the positive polarization branch, the phase angle ranging from 36 • to 116 • . The measured values of linear polarization are among the highest ever observed for a Solar system body. The covered interval of phase angle was not sufficiently extended to derive a firm determination of the P max parameter, but this appears to occur at a phase angle around 130 • and reaches more than 45% of linear polarization. Phaethon is the parent body of the Geminid meteor shower, and the real physical nature of this object (asteroid or comet) has been a long-debated subject. Our polarimetric measurements seem to support the asteroid hypothesis with a phasepolarization curve similar to the asteroid (2) Pallas, but further observations at smaller phase angles are needed to draw definitive conclusions.
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.
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