KELT-6b: A P~7.9 d Hot Saturn Transiting a Metal-Poor Star with a Long-Period Companion

• Published in: arXiv.org
• Main Authors: Collins, Karen A, Eastman, Jason D, Beatty, Thomas G, Siverd, Robert J, Gaudi, B Scott, Pepper, Joshua, Kielkopf, John F, John Asher Johnson, Howard, Andrew W, Fischer, Debra A, Manner, Mark, Bieryla, Allyson, Latham, David W, Fulton, Benjamin J, Gregorio, Joao, Buchhave, Lars A, Jensen, Eric L N, Stassun, Keivan G, Penev, Kaloyan, Crepp, Justin R, Hinkley, Sasha, Street, Rachel A, Cargile, Phillip, Mack, Claude E, Oberst, Thomas E, Avril, Ryan L, Mellon, Samuel N, McLeod, Kim K, Penny, Matthew T, Stefanik, Robert P, Berlind, Perry, Calkins, Michael L, Mao, Qingqing, Richert, Alexander J W, DePoy, Darren L, Esquerdo, Gilbert A, Gould, Andrew, Marshall, Jennifer L, Oelkers, Ryan J, Pogge, Richard W, Trueblood, Mark, Trueblood, Patricia
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 16.01.2014
• Subjects: Acceleration; Adaptive optics; Adaptive systems; Constraint modelling; Empirical analysis; Extrasolar planets; F stars; Gas giant planets; Gravitation; High resolution; Image detection; Image resolution; Metallicity; Photometry; Physics - Earth and Planetary Astrophysics; Planet detection; Planetary orbits; Radial velocity; Saturn; Stellar evolution
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1308.2296

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 \pm 43 K, log(g_*)=4.07_{-0.07}^{+0.04} and [Fe/H]=-0.28 \pm 0.04, with an inferred mass M_*=1.09 \pm 0.04 M_sun and radius R_star=1.58_{-0.09}^{+0.16} R_sun. The planetary companion has mass M_P=0.43 \pm 0.05 M_J, radius R_P=1.19_{-0.08}^{+0.13} R_J, surface gravity log(g_P)=2.86_{-0.08}^{+0.06}, and density rho_P=0.31_{-0.08}^{+0.07} g~cm^{-3}. The planet is on an orbit with semimajor axis a=0.079 \pm 0.001 AU and eccentricity e=0.22_{-0.10}^{+0.12}, which is roughly consistent with circular, and has ephemeris of T_c(BJD_TDB)=2456347.79679 \pm 0.00036 and P=7.845631 \pm 0.000046 d. 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 HD209458b, but orbits a host that is more metal poor than HD209458 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.