KELT-9 b, KELT-16 b, WASP-4 b and HD 97658

Making use of newly acquired photometric observations from CHEOPS (CHaracterising ExOplanet Satellite) and TESS (Transiting Exoplanet Survey Satellite), combined with archival transit and occultation data, we use MCMC (Markov chain Monte Carlo) algorithms to fit three models, a constant period model, an orbital decay model, and an apsidal precession model, to the data. We find that the KELT-9 system is best described by an apsidal precession model for now, with an orbital decay trend at over 2{sigma} being a possible solution as well.

A Keplerian orbit model with a constant orbital period fits the transit timings of KELT-16 b the best due to the scatter and scale of their error bars. The WASP-4 system is represented the best by an orbital decay model at a 5{sigma} significance, although apsidal precession cannot be ruled out with the present data. For HD 97658 b, using recently acquired transit observations, we find that a weak quadratic trend with a 1{sigma} deviation from a linear ephemeris describes the data best, ruling out a previously suspected strong quadratic trend.