Description
We report the discovery by the HATSouth network of HATS-18b: a 1.980+/-0.077M_J_, 1.337_-0.049_^+0.102^R_J_ planet in a 0.8378day orbit, around a solar analog star (mass 1.037+/-0.047M_{Sun}_ and radius 1.020_-0.031_^+0.057^R_{Sun}_) with V=14.067+/-0.040mag. The high planet mass, combined with its short orbital period, implies strong tidal coupling between the planetary orbit and the star. In fact, given its inferred age, HATS-18 shows evidence of significant tidal spin up, which together with WASP-19 (a very similar system) allows us to constrain the tidal quality factor for Sun-like stars to be in the range of 6.5<~log_10_(Q^*^/k_2_)<~7 even after allowing for extremely pessimistic model uncertainties. In addition, the HATS-18 system is among the best systems (and often the best system) for testing a multitude of star-planet interactions, be they gravitational, magnetic, or radiative, as well as planet formation and migration theories.
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