Transit timing variations in the WASP-4 planetary system*

Southworth, John; Dominik, M.; Jørgensen, U. G.; Andersen, M. I.; Bozza, V.; Burgdorf, M. J.; D’Ago, G.; Dib, S.; Jaimes, R. Figuera; Fujii, Y. I.; Gill, S.; Haikala, L. K.; Hinse, T. C.; Hundertmark, M.; Khalouei, E.; Korhonen, H.; Longa-Peña, P.; Mancini, L.; Peixinho, N.; Rabus, M.; Rahvar, S.; Sajadian, S.; Skottfelt, J.; Snodgrass, C.; Spyratos, P.; Tregloan-Reed, J.; Unda-Sanzana, E. and von Essen, C. (2019). Transit timing variations in the WASP-4 planetary system*. Monthly Notices of the Royal Astronomical Society, 490(3) pp. 4230–4236.



Abstract Transits in the planetary system WASP-4 were recently found to occur 80 s earlier than expected in observations from the TESS satellite. We present 22 new times of mid-transit that confirm the existence of transit timing variations, and are well fitted by a quadratic ephemeris with period decay dP/dt = −9.2 ± 1.1 ms yr−1. We rule out instrumental issues, stellar activity and the Applegate mechanism as possible causes. The light-time effect is also not favoured due to the non-detection of changes in the systemic velocity. Orbital decay and apsidal precession are plausible but unproven. WASP-4 b is only the third hot Jupiter known to show transit timing variations to high confidence. We discuss a variety of observations of this and other planetary systems that would be useful in improving our understanding of WASP-4 in particular and orbital decay in general.

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