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, logg =
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⊙ and radius R∗ =
1.209−0.035+0.047 R⊙. The planet has a radius RP =
1.399−0.049+0.069 RJ and mass MP = 0.679−0.038+0.039
MJ. 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 T0 = 2457066.72045±0.00027 BJDTDB and P =
4.1662739±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 Teq = 1377−23+28 K, assuming zero
albedo and perfect heat redistribution. KELT-10b receives an estimated
insolation of 0.817−0.054+0.068× 109 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
∼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.Comment: 20 pages, 13 figures, 7 tables, accepted for publication in MNRA