HAT-P-25b: A Hot-Jupiter Transiting a Moderately Faint G Star

We report the discovery of HAT-P-25b, a transiting extrasolar planet orbiting the V = 13.19 G5 dwarf star GSC 1788-01237, with a period P = 3.652836 ± 0.000019 days, transit epoch T_c = 2455176.85173 ± 0.00047 (BJD—barycentric Julian dates throughout the paper are calculated from Coordinated Universal Time, UTC), and transit duration 0.1174 ± 0.0017 days. The host star has a mass of 1.01 ± 0.03 M _⊙, radius of 0.96^+0.05 _{- 0.04} R _⊙, effective temperature 5500 ± 80 K, and metallicity [Fe/H] = +0.31 ± 0.08. The planetary companion has a mass of 0.567 ± 0.022 M _J and radius of 1.190^+0.081 _{- 0.056} R _J yielding a mean density of 0.42 ± 0.07 g cm^-3.

Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology. Keck time has been granted by NOAO (A201Hr), NASA (N018Hr and N167Hr), and the NASA Gemini-Keck time-exchange program (G329Hr). Based in part on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.