KELT-8b: a Highly Inflated hot Jupiter

KELT-8b: A highly inflated transiting hot Jupiter and a new technique for extracting high-precision radial velocities from noisy spectra

Authors:

Fulton et al

Abstract:

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 Teff=5754+54−55 K, logg=4.078+0.049−0.054, [Fe/H]=0.272±0.038, an inferred mass M∗=1.211+0.078−0.066 M⊙, and radius R∗=1.67+0.14−0.12 R⊙. The planetary companion has mass MP=0.867+0.065−0.061 MJ, radius RP=1.86+0.18−0.16 RJ, surface gravity loggP=2.793+0.072−0.075, and density ρP=0.167+0.047−0.038 g cm−3. The planet is on a roughly circular orbit with semimajor axis a=0.04571+0.00096−0.00084 AU and eccentricity e=0.035+0.050−0.025. The best-fit linear ephemeris is T0=2456883.4803±0.0007 BJDTDB and P=3.24406±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 logg 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 Teq=1675+61−55 K, assuming zero albedo and perfect heat redistribution, making it one of the best targets for future atmospheric characterization studies.