KELT-20b: A Giant Planet with a Period of P ∼ 3.5 days Transiting the V ∼ 7.6 Early A Star HD 185603
Bieryla, Allyson; Latham, David W.; Quinn, Samuel N.; Berlind, Perry; Calkins, Michael L.; Esquerdo, Gilbert A.; Pepper, Joshua; Stassun, Keivan G.; Siverd, Robert J.; Zhou, George; James, David; Kuhn, Rudolf B.; Wittenmyer, Robert A.; Fulton, Benjamin J.; Gould, Andrew; Collins, Karen A.; Ciardi, David R.; Lund, Michael B.; Rodriguez, Joseph E.; Oelkers, Ryan J.; Stevens, Daniel J.; Beatty, Thomas G.; Gaudi, B. Scott; Labadie-Bartz, Jonathan; Penev, Kaloyan; Johnson, Marshall C.; Colón, Knicole D.; Relles, Howard; Eastman, Jason D.; Cohen, David H.; Gregorio, Joao; Jensen, Eric L. N.; Johnson, John A.; Johnson, Samson A.; Joner, Michael D.; Kielkopf, John F.; McCrady, Nate; McLeod, Kim K.; Oberst, Thomas E.; Sliski, David H.; Stephens, Denise C.; Villanueva, Steven, Jr.; Zambelli, Roberto; Calchi Novati, Sebastiano; Patel, Rahul; DePoy, D. L.; Dressing, Courtney; Gonzales, Erica; Sergi, Anthony; Wright, Jason; Stockdale, Christopher; Marshall, Jennifer L.; Trueblood, Mark; Trueblood, Patricia; Corfini, Giorgio; Gagnon, Patrick; Wilson, Maurice
United States, Italy, Portugal, Sweden, South Africa, Australia
Abstract
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+0.14 M⊙, radius of R* = 1.561-0.064+0.058 R⊙, 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+0.070 RJ, 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 3σ 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 (λ =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-1 cm-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× 104 erg 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 third-brightest host (in V) of a transiting planet.