WASP-128b: a transiting brown dwarf in the dynamical-tide regime
Smalley, Barry; Hellier, Coel; Triaud, Amaury H. M. J.; Anderson, David R.; Lendl, Monika; Udry, Stéphane; Gillon, Michaël; Delrez, Laetitia; Jehin, Emmanuël; Queloz, Didier; Bouchy, François; Maxted, Pierre F. L.; Pepe, Francesco; Pollacco, Don; Ségransan, Damien; Collier Cameron, Andrew; West, Richard; Hodžić, Vedad
United Kingdom, Switzerland, Belgium, Austria
Abstract
Massive companions in close orbits around G dwarfs are thought to undergo rapid orbital decay due to runaway tidal dissipation. We report here the discovery of WASP-128b, a brown dwarf discovered by the WASP survey transiting a G0V host on a 2.2 d orbit, where the measured stellar rotation rate places the companion in a regime where tidal interaction is dominated by dynamical tides. Under the assumption of dynamical equilibrium, we derive a value of the stellar tidal quality factor log {Q_\star ^' }} = 6.96 ± 0.19. A combined analysis of ground-based photometry and high-resolution spectroscopy reveals a mass and radius of the host, M_\star = 1.16± 0.04 M_{⊙}, R_\star = 1.16± 0.02 R_{⊙}, and for the companion, M_b = 37.5± 0.8 M_J, R_b = 0.94± 0.02 R_J, placing WASP-128b in the driest parts of the brown dwarf desert, and suggesting a mild inflation for its age. We estimate a remaining lifetime for WASP-128b similar to that of some ultra-short period massive hot Jupiters, and note it may be a propitious candidate for measuring orbital decay and testing tidal theories.