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The 0.5MJ transiting exoplanet WASP-13b
We report the discovery of WASP-13b, a low-mass Mp = 0.46+0.06 ?0.05 MJ transiting exoplanet with an orbital period of 4.35298 +/- 0.00004 days. The transit has a depth of 9 mmag, and although our follow-up photometry does not allow us to constrain the impact parameter well (0 < b < 0.46), with radius in the range Rp ? 1.06?1.21 RJ the location of WASP-13b in the mass-radius plane is nevertheless consistent with H/He-dominated, irradiated, low core mass and core-free theoretical models. The G1V host star is similar to the Sun in mass (M? = 1.03+0.11 ?0.09 M ) and metallicity ([M/H] = 0.0 + / - 0.2), but is possibly older (8.5+5.5 ?4.9 Gyr).