KELT-6b: A P ∼ 7.9 day hot saturn transiting a metal-poor star with a long-period companion

Karen A. Collins, Jason D. Eastman, Thomas G. Beatty, Robert J. Siverd, B. Scott Gaudi, Joshua Pepper, John F. Kielkopf, John Asher Johnson, Andrew W. Howard, Debra A. Fischer, Mark Manner, Allyson Bieryla, David W. Latham, Benjamin J. Fulton, Joao Gregorio, Lars A. Buchhave, Eric L.N. Jensen, Keivan G. Stassun, Kaloyan Penev, Justin R. CreppSasha Hinkley, Rachel A. Street, Phillip Cargile, Claude E. MacK, Thomas E. Oberst, Ryan L. Avril, Samuel N. Mellon, Kim K. McLeod, Matthew T. Penny, Robert P. Stefanik, Perry Berlind, Michael L. Calkins, Qingqing Mao, Alexander J.W. Richert, Darren L. Depoy, Gilbert A. Esquerdo, Andrew Gould, Jennifer L. Marshall, Ryan J. Oelkers, Richard W. Pogge, Mark Trueblood, Patricia Trueblood

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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* = 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.

Original languageEnglish (US)
Article number39
JournalAstronomical Journal
Volume147
Issue number2
DOIs
StatePublished - Feb 2014

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Collins, K. A., Eastman, J. D., Beatty, T. G., Siverd, R. J., Gaudi, B. S., Pepper, J., Kielkopf, J. F., Johnson, J. A., Howard, A. W., Fischer, D. A., Manner, M., Bieryla, A., Latham, D. W., Fulton, B. J., Gregorio, J., Buchhave, L. A., Jensen, E. L. N., Stassun, K. G., Penev, K., ... Trueblood, P. (2014). KELT-6b: A P ∼ 7.9 day hot saturn transiting a metal-poor star with a long-period companion. Astronomical Journal, 147(2), [39]. https://doi.org/10.1088/0004-6256/147/2/39