KELT-20b: A Giant Planet with a Period of P ∼ 3.5 days Transiting the v ∼ 7.6 Early A Star HD 185603

Michael B. Lund, Joseph E. Rodriguez, George Zhou, B. Scott Gaudi, Keivan G. Stassun, Marshall C. Johnson, Allyson Bieryla, Ryan J. Oelkers, Daniel J. Stevens, Karen A. Collins, Kaloyan Penev, Samuel N. Quinn, David W. Latham, Steven Villanueva, Jason D. Eastman, John F. Kielkopf, Thomas E. Oberst, Eric L.N. Jensen, David H. Cohen, Michael D. JonerDenise C. Stephens, Howard Relles, Giorgio Corfini, Joao Gregorio, Roberto Zambelli, Gilbert A. Esquerdo, Michael L. Calkins, Perry Berlind, David R. Ciardi, Courtney Dressing, Rahul Patel, Patrick Gagnon, Erica Gonzales, Thomas G. Beatty, Robert J. Siverd, Jonathan Labadie-Bartz, Rudolf B. Kuhn, Knicole D. Colón, David James, Joshua Pepper, Benjamin J. Fulton, Kim K. McLeod, Christopher Stockdale, Sebastiano Calchi Novati, D. L. DePoy, Andrew Gould, Jennifer L. Marshall, Mark Trueblood, Patricia Trueblood, John A. Johnson, Jason Wright, Nate McCrady, Robert A. Wittenmyer, Samson A. Johnson, Anthony Sergi, Maurice Wilson, David H. Sliski

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We report the discovery of KELT-20b, a hot Jupiter transiting a V ∼7.6 early A star, HD 185603, with an orbital period of P ≃3.47 days. Archival and follow-up photometry, Gaia parallax, radial velocities, Doppler tomography, and AO imaging were used to confirm the planetary nature of KELT-20b and characterize the system. From global modeling we infer that KELT-20 is a rapidly rotating (v sin I∗ ≃ 120 km s-1 ) A2V star with an effective temperature of Teff=8730 -260 +250 K, mass of M∗+1.76-0.20 +0.14MO, radius of R∗= 1.561-0.064+0.058RO,surface gravity of log g ∗=4.292-0.020+0.017, and age of ≳600 Myr. The planetary companion has a radius of Rp=1.735 -0.075 +0.070Rj, a semimajor axis of a =0.0542-0.0021+0.0014 au, and a linear ephemeris of BJDTDB=2457503.120049 ± 0.000190+E(3.4741070± 0.0000019). We place a 3s upper limit of ∼ 3.5 MJ on the mass of the planet. Doppler tomographic measurements indicate that the planetary orbit normal is well aligned with the projected spin axis of the star (l = 3 °.4± 2 °.1). The inclination of the star is constrained to 24°.4 > I ∗ > 155 °.6, implying a three-dimensional spin-orbit alignment of 1°.3 > ψ > 69°.8. KELT-20b receives an insolation flux of∼8× 109 erg s-1cm-2, implying an equilibrium temperature of of ∼ 2250 K, assuming zero albedo and complete heat redistribution. Due to the high stellar Teff, KELT-20b also receives an ultraviolet (wavelength d ≤ 91.2 nm) insolation flux of ∼9.1×104erg s-1 cm-2, possibly indicating significant atmospheric ablation. Together with WASP-33, Kepler-13 A, HAT-P-57, KELT-17, and KELT-9, KELT-20 is the sixth A star host of a transiting giant planet, and the thirdbrightest host (in V) of a transiting planet.

Original languageEnglish
Article number194
JournalAstronomical Journal
Issue number5
StatePublished - Nov 2017


  • methods: observational
  • planets and satellites: detection
  • planets and satellites: gaseous planets
  • stars: individual (HD 185603)
  • techniques: photometric
  • techniques: radial velocities


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