A Metal - Rich Low - Density Transiting Hot Jupiter

We describe the discovery of HAT-P-4b, a low-density extrasolar planet transiting BD+36 2593, a V = 11.2mag slightly evolved metal-rich late F star. The planet’s orbital period is 3.056536 ± 0.000057d with a mid-transit epoch of 2, 454, 245.8154± 0.0003 (HJD). Based on high-precision photometric and spectroscopic data, and by using transit light curve modeling, spectrum analysis and evolutionary models, we derive the following planet parameters: Mp= 0.68±0.04MJ, Rp= 1.27±0.05RJ, ρp= 0.41±0.06g cm −3 and a = 0.0446±0.0012AU. Because of its relatively large radius, together with its assumed high metallicity of that of its parent star, this planet adds to the theoretical challenges to explain inflated extrasolar planets. Subject headings: planetary systems: individual: HAT-P-4b — stars: individual: BD+36 2593 — techniques: photometric — techniques: spectroscopic