We announce the discovery of a highly inflated transiting hot Jupiter discovered by the KELT-North survey .
A global analysis including constraints from isochrones indicates that the V = 10.8 host star ( HD 343246 ) is a mildly evolved , G dwarf with T _ { eff } = 5754 _ { -55 } ^ { +54 } K , \log { g } = 4.078 _ { -0.054 } ^ { +0.049 } , [ Fe / H ] = 0.272 \pm 0.038 , an inferred mass M _ { * } = 1.211 _ { -0.066 } ^ { +0.078 } M _ { \odot } , and radius R _ { * } = 1.67 _ { -0.12 } ^ { +0.14 } R _ { \odot } .
The planetary companion has mass M _ { P } = 0.867 _ { -0.061 } ^ { +0.065 } M _ { J } , radius R _ { P } = 1.86 _ { -0.16 } ^ { +0.18 } R _ { J } , surface gravity \log { g _ { P } } = 2.793 _ { -0.075 } ^ { +0.072 } , and density \rho _ { P } = 0.167 _ { -0.038 } ^ { +0.047 } g cm ^ { -3 } .
The planet is on a roughly circular orbit with semimajor axis a = 0.04571 _ { -0.00084 } ^ { +0.00096 } AU and eccentricity e = 0.035 _ { -0.025 } ^ { +0.050 } .
The best-fit linear ephemeris is T _ { 0 } = 2456883.4803 \pm 0.0007 BJD _ { TDB } and P = 3.24406 \pm 0.00016 days .
This planet is one of the most inflated of all known transiting exoplanets , making it one of the few members of a class of extremely low density , highly-irradiated gas giants .
The low stellar \log { g } and large implied radius are supported by stellar density constraints from follow-up light curves , plus an evolutionary and space motion analysis .
We also develop a new technique to extract high precision radial velocities from noisy spectra that reduces the observing time needed to confirm transiting planet candidates .
This planet boasts deep transits of a bright star , a large inferred atmospheric scale height , and a high equilibrium temperature of T _ { eq } = 1675 ^ { +61 } _ { -55 } K , assuming zero albedo and perfect heat redistribution , making it one of the best targets for future atmospheric characterization studies .