HAT - P - 10 b : A LIGHT AND MODERATELY HOT JUPITER TRANSITING A K DWARF

We report on the discovery of HAT-P-10b, the lowest mass (0.46 ± 0.03MJ) transiting extrasolar planet (TEP) discovered to date by transit searches. HAT-P-10b orbits the moderately bright V=11.89 K dwarf GSC 02340-01714, with a period P = 3.7224690 ± 0.0000067 d, transit epoch Tc = 2454729.90631± 0.00030 (BJD) and duration 0.1100 ± 0.0015d. HAT-P-10b has a radius of 1.05 −0.03RJ yielding a mean density of 0.498± 0.064 g cm. Comparing these observations with recent theoretical models we find that HAT-P-10 is consistent with a ∼ 4.5Gyr, coreless, pure hydrogen and helium gas giant planet. With an equilibrium temperature of Teq = 1030 +26 −19K, HAT-P-10b is one of the coldest TEPs. Curiously, its Safronov number θ = 0.047± 0.003 falls close to the dividing line between the two suggested TEP populations. Subject headings: planetary systems — stars: individual (HAT-P-10, GSC 02340-01714) techniques: spectroscopic, photometric