Robert J. Siverd, Las Cumbres Observatory Global Telescope Network, Inc
Karen A. Collins, Harvard-Smithsonian Center for Astrophysics
George Zhou, Harvard-Smithsonian Center for Astrophysics
Samuel N. Quinn, Harvard-Smithsonian Center for Astrophysics
B. Scott Gaudi, The Ohio State University
Keivan G. Stassun, Vanderbilt University
Marshall C. Johnson, The Ohio State University
Allyson Bieryla, Harvard-Smithsonian Center for Astrophysics
David W. Latham, Harvard-Smithsonian Center for Astrophysics
David R. Ciardi, California Institute of Technology
Joseph E. Rodriguez, Harvard-Smithsonian Center for Astrophysics
Kaloyan Penev, The University of Texas at Dallas
Marc Pinsonneault, The Ohio State University
Joshua Pepper, Lehigh University
Jason D. Eastman, Harvard-Smithsonian Center for Astrophysics
Howard Relles, Harvard-Smithsonian Center for Astrophysics
John F. Kielkopf, University of Louisville
Joao Gregorio, Atalaia Group and CROW Observatory
Thomas E. Oberst, Westminster College, New Wilmington
Giulio Francesco Aldi, Università degli Studi di Salerno
Gilbert A. Esquerdo, Harvard-Smithsonian Center for Astrophysics
Michael L. Calkins, Harvard-Smithsonian Center for Astrophysics
Perry Berlind, Harvard-Smithsonian Center for Astrophysics
Courtney D. Dressing, Division of Geological and Planetary Sciences
Rahul Patel, Infrared Processing & Analysis Center
Daniel J. Stevens, The Ohio State University
Thomas G. Beatty, Pennsylvania State University
Michael B. Lund, Vanderbilt University
Jonathan Labadie-Bartz, Lehigh University
Rudolf B. Kuhn, South African Astronomical Observatory
Knicole D. Colón, NASA Goddard Space Flight Center
David James, University of Washington
Xinyu Yao, Lehigh University

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We present the discovery of the giant planet KELT-19Ab, which transits the moderately bright (V ∼ 9.9) A8V star TYC 764-1494-1 with an orbital period of 4.61 days. We confirm the planetary nature of the companion via a combination of radial velocities, which limit the mass to ≳4.1 MJ (3s), and a clear Doppler tomography signal, which indicates a retrograde projected spin-orbit misalignment of λ = -179.7-3.8+3.7 degrees. Global modeling indicates that the Teff = 7500 ±110 K host star has M M = 1.62+0.20-0.25 and R = 1.83 0.10 R. The planet has a radius of RP = 1.91 0.11 RJ and receives a stellar insolation flux of ∼ 3.2 10 erg s-1 cm-2, leading to an inferred equilibrium temperature of Teq ∼ 1935 K assuming zero albedo and complete heat redistribution. With a v I sin 84.8 ±2.0 km s = -1, the host is relatively slowly rotating compared to other stars with similar effective temperatures, and it appears to be enhanced in metallic elements but deficient in calcium, suggesting that it is likely an Am star. KELT-19A would be the first detection of an Am host of a transiting planet of which we are aware. Adaptive optics observations of the system reveal the existence of a companion with late-G9V/early-K1V spectral type at a projected separation of »160 au. Radial velocity measurements indicate that this companion is bound. Most Am stars are known to have stellar companions, which are often invoked to explain the relatively slow rotation of the primary. In this case, the stellar companion is unlikely to have caused the tidal braking of the primary. However, it may have emplaced the transiting planetary companion via the Kozai-Lidov mechanism.

Publication Source (Journal or Book title)

Astronomical Journal