KELT-10b: the first transiting exoplanet from the KELT-South survey - a hot sub-Jupiter transiting a V = 10.7 early G-star

We report the discovery of KELT-10b, the first transiting exoplanet discovered using the KELT-South telescope. KELT-10b is a highly inflated sub-Jupiter mass planet transiting a relatively bright V = 10.7 star (TYC 8378-64-1), with Teff = 5948±74 K, log g = 4.319 -0.030 to +0.020 and [Fe/H] = 0.09 -0.10 to +0.11, an inferred mass M* = 1.112 -0.061 to +0.055 M⊙ and radius R* = 1.209 -0.038 to +0.047 R⊙. The planet has a radius Rp = 1.399 -0.049 to +0.069 RJ and mass Mp = 0.679 -0.038 to +0.039 MJ. The planet has an eccentricity consistent with zero and a semi-major axis a = 0.05250 -0.00097 to +0.00086 au. The best fitting linear ephemeris is T0 = 2457066.720 45±0.00027 BJDTDB and P = 4.1662739 ± 0.0000063 days. This planet joins a group of highly inflated transiting exoplanets with a radius larger and a mass less than that of Jupiter. The planet, which boasts deep transits of 1.4%, has a relatively high equilibrium temperature of Teq = 1377 -23 to +28 K, assuming zero albedo and perfect heat redistribution. KELT-10b receives an estimated insolation of 0.817 -0.054 to +0.068 X10 to the 9 erg s-1 cm-2, which places it far above the insolation threshold above which hot Jupiters exhibit increasing amounts of radius inflation. Evolutionary analysis of the host star suggests that KELT-10b may not survive beyond the current subgiant phase, depending on the rate of in-spiral of the planet over the next few Gyr. The planet transits a relatively bright star and exhibits the third largest transit depth of all transiting exoplanets with V < 11 in the southern hemisphere, making it a promising candidate for future atmospheric characterization studies