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 ( \mbox { $T _ { eff } $ } = 6000 \pm 100 K , [ Fe/H ] = -0.05 \pm 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 0.14 d. 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 3.533 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 \pm 0.02 M _ { Jup } and a radius R _ { p } = 1.12 \pm 0.04 R _ { Jup } .
In addition , there is a linear trend of 40 m s ^ { -1 } y ^ { -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 .