On the orbit of the short-period exoplanet WASP-19b

Abstract

WASP-19b has the shortest orbital period of any known exoplanet, orbiting at only 1.2 times the Roche tidal radius. By observing the Rossiter-McLaughlin effect we show that WASP-19b's orbit is aligned, with λ = 46 52. Using, in addition, a spectroscopic vsin I and the observed rotation period we conclude that the obliquity, ψ, is less than 20°. Further, the eccentricity of the orbit is less than 0.02. We argue that hot Jupiters with orbital periods as short as that of WASP-19b are two orders of magnitude less common than hot Jupiters at the 3-4 day "pileup." We discuss the evolution of WASP-19b's orbit and argue that most likely it was first moved to near twice the Roche limit by third-body interactions, and has since spiralled inward to its current location under tidal decay. This is compatible with a stellar tidal-dissipation quality factor, Q′*, of order 10 7. © 2011. The American Astronomical Society. All rights reserved.