WASP-4 mid-transit times

Theoretical considerations indicate that such efficient dissipation is possible due to internal gravity waves in the radiative core of WASP-4, but only in our models with a more evolved host star, possibly near the end of its main-sequence lifetime, and with a larger radius than the observed one. Our main-sequence models produce only about a third of the required dissipation (Q'_*r_~2-5x10^5^). Therefore, the observed orbital decay can only be explained by a slightly larger or more evolved host, resembling the case for WASP-12.

Our findings highlight the need for further stellar modelling and improvement in our current understanding of tidal dissipation mechanisms driving orbital decay in close-in exoplanetary systems.