WASP-25b: a 0.6 M_J planet in the Southern hemisphere

We report the detection of a 0.6 M_J extrasolar planet by WASP-South, WASP-25b, transiting its solar-type host star every 3.76 days. A simultaneous analysis of the WASP and FTS photometry and CORALIE spectroscopy yields a planet of R_p = 1.26 R_J and M p = 0.58 M_J around a slightly metal-poor solar-type host star, [Fe/H] = -0.05±0.10, of R_∗ = 0.95 R_⊙ and M_∗ = 1.00 M_⊙ . WASP-25b is found to have a density of ρ_p = 0.29 ρ_J , a low value for a sub-Jupiter mass planet. We investigate the relationship of planetary radius to planetary equilibrium temperature and host star metallicity for transiting exoplanets with a similar mass to WASP-25b. We find that the relation R_p = 0.3691 − 0.3481[Fe/H] + 6.309(Teq /1000) matches the observed radii of these planets.