WASP-128b: a transiting brown dwarf in the dynamical-tide regime. Issue 4 (14th September 2018) - Hodžić, Vedad
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 $2.2\, \mathrm{d}$ 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 $\log {Q_\star ^{\prime }} = 6.96 \pm 0.19$ . A combined analysis of ground-based photometry and high-resolution spectroscopy reveals a mass and radius of the host, $M_\star = 1.16\pm 0.04\, \mathrm{M}_{\odot }$, $R_\star = 1.16\pm 0.02\, \mathrm{R}_{\odot }$, and for the companion, $M_\mathrm{b} = 37.5\pm 0.8\, M_\mathrm{J}$, $R_\mathrm{b} = 0.94\pm 0.02\, R_\mathrm{J}$, 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.