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 T$_{ eff}$ = $5948\pm74$ K, $\log{ g}$ = $4.319_{ -0.030}^{ +0.020}$ and [Fe/H] = $0.09_{ -0.10}^{ +0.11}$, an inferred mass M$_{ *}$ = $1.112_{ -0.061}^{ +0.055}$ M$_{ \odot}$ and radius R$_{ *}$ = $1.209_{ -0.035}^{ +0.047}$ R$_{ \odot}$. The planet has a radius R$_{ P}$ = $1.399_{ -0.049}^{ +0.069}$ R$_{ J}$ and mass M$_{ P}$ = $0.679_{ -0.038}^{ +0.039}$ M$_{ J}$. The planet has an eccentricity consistent with zero and a semi-major axis $a$ = $0.05250_{ -0.00097}^{ +0.00086}$ AU. The best fitting linear ephemeris is $T_{ 0}$ = 2457066.72045$\pm$0.00027 BJD$_{ TDB}$ and P = 4.1662739$\pm$0.0000063 days. This planet joins a group of highly inflated transiting exoplanets with a radius much larger and a mass much less than those of Jupiter. The planet, which boasts deep transits of 1.4%, has a relatively high equilibrium temperature of T$_{ eq}$ = $1377_{ -23}^{ +28}$ K, assuming zero albedo and perfect heat redistribution. KELT-10b receives an estimated insolation of $0.817_{ -0.054}^{ +0.068}$ $\times$ 10$^9$ 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 is unlikely to survive beyond the current subgiant phase, due to a concomitant in-spiral of the planet over the next $\sim$1 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.
Categories: astro-ph.EP