KELT-6b: A P ~ 7.9 Day Hot Saturn Transiting a Metal-poor Star with a Long-period Companion

February 2014 • 2014AJ....147...39C

Authors • Collins, Karen A. • Eastman, Jason D. • Beatty, Thomas G. • Siverd, Robert J. • Gaudi, B. Scott • Pepper, Joshua • Kielkopf, John F. • Johnson, John Asher • 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

Abstract • 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_\star =4.07_{-0.07}^{+0.04}, and [Fe/H] = -0.28 ± 0.04, with an inferred mass M sstarf = 1.09 ± 0.04 M and radius R_\star =1.58_{-0.09}^{+0.16} \,R_\odot. The planetary companion has mass MP = 0.43 ± 0.05 M Jup, radius R_{P}=1.19_{-0.08}^{+0.13} \,R_Jup, 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 ± 0.001 AU and eccentricity e=0.22_{-0.10}^{+0.12}, which is roughly consistent with circular, and has ephemeris of T c(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.

KELT is a joint project of The Ohio State University, Vanderbilt University, and Lehigh University.


IPAC Authors


Benjamin Fulton

Assistant Scientist