* Astronomy

Title: KELT-8b: A highly inflated transiting hot Jupiter and a new technique for extracting high-precision radial velocities from noisy spectra
Author: Benjamin J. Fulton, Karen A. Collins, B. Scott Gaudi, Keivan G. Stassun, Joshua Pepper, Thomas G. Beatty, Robert J. Siverd, Kaloyan Penev, Andrew W. Howard, Christoph Baranec, Giorgio Corfini, Jason D. Eastman, Joao Gregorio, Nicholas M. Law, Michael B. Lund, Thomas E. Oberst, Matthew T. Penny, Reed Riddle, Joseph E. Rodriguez, Daniel J. Stevens, Roberto Zambelli, Carl Ziegler, Allyson Bieryla, Giuseppe D`Ago, Darren L. DePoy, Eric L. N. Jensen, John F. Kielkopf, David W. Latham, Mark Manner, Jennifer Marshall, Kim K. McLeod, Phillip A. Reed

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, logg=4.078_{-0.054}^{+0.049}, [Fe/H]=0.272±0.038, an inferred mass M_*=1.211_{-0.066}^{+0.078} solar masses, and radius R_*=1.67_{-0.12}^{+0.14} solar radii. 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±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 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.

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