We report the discovery of a low-density exoplanet transiting an 11th magnitude star in the Southern hemisphere .
WASP-15b , which orbits its host star with a period P = 3.7520656 \pm 0.0000028 d has a mass M _ { p } = 0.542 \pm 0.050 M _ { J } and radius R _ { p } = 1.428 \pm 0.077 R _ { J } , and is therefore the one of least dense transiting exoplanets so far discovered ( \rho _ { p } = 0.247 \pm 0.035 g cm ^ { -3 } ) .
An analysis of the spectrum of the host star shows it to be of spectral type around F5 , with an effective temperature T _ { eff } = 6300 \pm 100 K and [ { Fe / H } ] = -0.17 \pm 0.11 .