Karen A. Collins, University of Louisville
Jason D. Eastman, Las Cumbres Observatory Global Telescope Network, Inc
Thomas G. Beatty, The Ohio State University
Robert J. Siverd, Vanderbilt University
B. Scott Gaudi, The Ohio State University
Joshua Pepper, Vanderbilt University
John F. Kielkopf, University of Louisville
John Asher Johnson, California Institute of Technology
Andrew W. Howard, University Hawaii Institute for Astronomy
Debra A. Fischer, Yale University
Mark Manner, Spot Observatory
Allyson Bieryla, Harvard-Smithsonian Center for Astrophysics
David W. Latham, Harvard-Smithsonian Center for Astrophysics
Benjamin J. Fulton, University Hawaii Institute for Astronomy
Joao Gregorio, Atalaia Group and CROW Observatory
Lars A. Buchhave, Niels Bohr Institutet
Eric L.N. Jensen, Swarthmore College
Keivan G. Stassun, Vanderbilt University
Kaloyan Penev, Princeton University
Justin R. Crepp, University of Notre Dame
Sasha Hinkley, California Institute of Technology
Rachel A. Street, Las Cumbres Observatory Global Telescope Network, Inc
Phillip Cargile, Vanderbilt University
Claude E. MacK, Vanderbilt University
Thomas E. Oberst, Westminster College, New Wilmington
Ryan L. Avril, Westminster College, New Wilmington
Samuel N. Mellon, Westminster College, New Wilmington
Kim K. McLeod, Wellesley College
Matthew T. Penny, The Ohio State University
Robert P. Stefanik, Harvard-Smithsonian Center for Astrophysics
Perry Berlind, Harvard-Smithsonian Center for Astrophysics
Michael L. Calkins, Harvard-Smithsonian Center for Astrophysics
Qingqing Mao, Vanderbilt University

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We report the discovery of KELT-6b, a mildly inflated Saturn-mass planet transiting a metal-poor host. The initial transit signal was identified in KELT-North survey data, and the planetary nature of the occulter was established using a combination of follow-up photometry, high-resolution imaging, high-resolution spectroscopy, and precise radial velocity measurements. The fiducial model from a global analysis including constraints from isochrones indicates that the V = 10.38 host star (BD+31 2447) is a mildly evolved, late-F star with T eff = 6102 ± 43 K, log g* = 4.07 +0.04-0.07, and [Fe/H] = -0.28 ± 0.04, with an inferred mass M· = 1.09 ± 0.04M· and radius R· = 1.58+0.16-0.09 R ·. The planetary companion has mass MP = 0.43 ± 0.05MJup, radius RP = 1.19+0.13-0.08 RJup, surface gravity log gP = 2.86+0.06-0.08, and density .P = 0.31+0.07-0.08 g cm-3. The planet is on an orbit with semimajor axis a = 0.079 ± 0.001 AU and eccentricity e = 0.22+0.12-0.10, which is roughly consistent with circular, and has ephemeris of Tc(BJDTDB) = 2456347.79679 ± 0.00036 and P = 7.845631 ± 0.000046 days. Equally plausible fits that employ empirical constraints on the host-star parameters rather than isochrones yield a larger planet mass and radius by ∼4}-7}. KELT-6b has surface gravity and incident flux similar to HD 209458b, but orbits a host that is more metal poor than HD 209458 by ∼0.3 dex. Thus, the KELT-6 system offers an opportunity to perform a comparative measurement of two similar planets in similar environments around stars of very different metallicities. The precise radial velocity data also reveal an acceleration indicative of a longer-period third body in the system, although the companion is not detected in Keck adaptive optics images. © 2014. The American Astronomical Society. All rights reserved.

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Astronomical Journal