On the orbit of the short-period exoplanet WASP-19b
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 lambda = 4.6 +/- 5.2 degrees. Further, the eccentricity of the orbit is less than 0.02. We discuss the evolution of WASP-19b's orbit and argue that most likely it was moved to near twice the Roche limit by third-body interactions, and has since spiralled inwards to its current location. This is compatible with a stellar tidal-dissipation quality factor, Q_star, of order 10^7.
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