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

November 2017 • 2017AJ....154..194L

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

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 T_eff= 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 R_P= 1.735_-0.075^+0.070 R_J, a semimajor axis of a=0.0542_-0.0021^+0.0014 au, and a linear ephemeris of BJD_TDB=2457503.120049± 0.000190 +E(3.4741070± 0.0000019). We place a 3σ upper limit of ∼ 3.5 M_J 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 T_eff, 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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2017AJ....154..194L
• PDF https://iopscience.iop.org/article/10.3847/1538-3881/aa8f95/pdf
• PDF https://stacks.iop.org/1538-3881/154/194/pdf
• PREPRINT http://arxiv.org/abs/1707.01518
• DATA http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?type=REFERENCE&bibcode=2017AJ....154..194L
• DATA https://irsa.ipac.caltech.edu/bibdata/2017/L/2017AJ....154..194L.html
• ELECTR https://doi.org/10.3847%2F1538-3881%2Faa8f95