We report the discovery by the HATSouth network of HATS-18 b: a 1.980 +/- 0.077 Mj, 1.337 +0.102 -0.049 Rj planet in a 0.8378 day orbit, around a solar analog star (mass 1.037 +/- 0.047 Msun, and radius 1.020 +0.057 -0.031 Rsun) with V=14.067 +/- 0.040 mag. 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 6.5 <= lg(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.
@article{arxiv.1606.00848,
title = {HATS-18 b: An Extreme Short--Period Massive Transiting Planet Spinning Up Its Star},
author = {Kaloyan M. Penev and Joel D. Hartman and Gaspar A. Bakos and Simona Ciceri and Rafael Brahm and Daniel Bayliss and Joao Bento and Andr'es Jord'an and Zoltan Csubry and W. Bhatti and Miguel de Val-Borro and Néstor Espinoza and George Zhou and Luigi Mancini and Markus Rabus and Vincent Suc and Thomas Henning and Brian P. Schmidt and Robert W. Noyes and J. L'az'ar and Istvan Papp and P. S'ari},
journal= {arXiv preprint arXiv:1606.00848},
year = {2016}
}