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 +/- 100K, [Fe/H]= -0.05 +/- 0.08). The lightcurve of the star
obtained with the WASP-South instrument shows periodic transit-like features
with a depth of about 1% and a duration of 0.14d. The presence of a
transit-like feature in the lightcurve is confirmed using z-band photometry
obtained with Faulkes Telescope South. High resolution spectroscopy obtained
with the CORALIE and HARPS spectrographs confirm the presence of a planetary
mass companion with an orbital period of 3.533d 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 +/- 0.02)M_Jup and a radius R_p = (1.12 +/- 0.04)R_Jup. In addition,
there is a linear trend of 40m/s/y 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 or a second
 planet.