WASP-22 b: A TRANSITING HOT JUPITER PLANET IN A HIERARCHICAL TRIPLE SYSTEM

We report the discovery of a transiting planet orbiting the star TYC 6446-326-1. The star, WASP-22, is a moderately bright (V = 12.0) solar-type star (T-eff = 6000 +/- 100 K, [Fe/H]= -0.05 +/- 0.08). The light curve of the star obtained with the WASP-South instrument shows periodic transit-like features with a depth of about 1% and a duration of 0.14 days. The presence of a transit-like feature in the light curve is confirmed using z-band photometry obtained with Faulkes Telescope South. High-resolution spectroscopy obtained with the CORALIE and HARPS spectrographs confirms the presence of a planetary mass companion with an orbital period of 3.533 days in a near-circular orbit. From a combined analysis of the spectroscopic and photometric data assuming that the star is a typical main-sequence star we estimate that the planet has a mass M-P = 0.56 +/- 0.02M(Jup) and a radius R-P = 1.12 +/- 0.04R(Jup). In addition, there is a linear trend of 40 m s(-1) yr(-1) in the radial velocities measured over 16 months, from which we infer the presence of a third body with a long-period orbit in this system. The companion may be a low mass M-dwarf, a white dwarf, or a second planet.