A search for transit timing variations in the HATS-18 planetary system

Funding: AJB was supported by STFC grants ST/S000275/1 and ST/W000873/1. UGJ acknowledges funding from the Novo Nordisk Foundation Interdisciplinary Synergy Programme grant no. NNF19OC0057374 and from the European Union H2020-MSCA-ITN-2019 under Grant no. 860470 (CHAMELEON). PLP was partly funded by Programa de Iniciación en Investigación-Universidad de Antofagasta, INI-17-03. NP’s work was supported by Fundacaão para a Ciência e a Tecnologia (FCT) through the research grants UIDB/04434/2020 and UIDP/04434/2020. This research has received funding from the Europlanet 2024 Research Infrastructure (RI) programme. RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 871149. This research received financial support from the National Research Foundation (NRF; No. 2019R1I1A1A01059609).HATS-18 b is a transiting planet with a large mass and a short orbital period, and is one of the best candidates for the detection of orbital decay induced by tidal effects. We present extensive photometry of HATS-18 from which we measure 27 times of mid-transit. Two further transit times were measured from data from the Transiting Exoplanet Survey Satellite (TESS) and three more taken from the literature. The transit timings were fitted with linear and quadratic ephemerides and an upper limit on orbital decay was determined. This corresponds to a lower limit on the modified stellar tidal quality factor of Q*′ > 105.11±0.04. This is at the cusp of constraining the presence of enhanced tidal dissipation due to internal gravity waves. We also refine the measured physical properties of the HATS-18 system, place upper limits on the masses of third bodies, and compare the relative performance of TESS and the 1.54 m Danish Telescope in measuring transit times for this system.Publisher PDFPeer reviewe