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

Lund, Michael B. and Ciardi, David R. and Gagnon, Patrick and Dressing, Courtney and Patel, Rahul and Calchi Novati, Sebastiano and Fulton, Benjamin J. (2017) KELT-20b: A Giant Planet with a Period of P ~ 3.5 days Transiting the V ~ 7.6 Early A Star HD 185603. Astronomical Journal, 154 (5). Art. No. 194. ISSN 1538-3881.

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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 (ν sin I* ≃ 120 km s^(-1)) A2V star with an effective temperature of T_(eff) = 8730^(+250)_(-260) K, mass of, M* = ^(+0.14)_(-0.20) M⊙ radius of, R* = 1.561^(+0.058)_(-0.064) R⊙ surface gravity of, log g* = 4.292^(+0.017)_(-0.020), and age of ≾600 Myr. The planetary companion has a radius of R_P = 1.735^(+0.070)_(-0.075) R_J, a semimajor axis of a = 0.0542^(+0.0014)_(-0.0021) 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 x 10^9 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 x 10^4 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lund, Michael B.0000-0003-2527-1598
Ciardi, David R.0000-0002-5741-3047
Dressing, Courtney0000-0001-8189-0233
Patel, Rahul0000-0002-5025-6827
Calchi Novati, Sebastiano0000-0002-7669-1069
Fulton, Benjamin J.0000-0003-3504-5316
Additional Information:© 2017 The American Astronomical Society. Received 2017 July 5; revised 2017 September 14; accepted 2017 September 21; published 2017 October 20. We would like to thank the anonymous referee for thorough and useful report. Work performed by J.E.R. was supported by the Harvard Future Faculty Leaders Postdoctoral fellowship. D.J.S. and B.S.G. were partially supported by NSF CAREER grant AST-1056524. Work by S.V.Jr. is supported by the National Science Foundation Graduate Research Fellowship under grant no. DGE-1343012. K.G.S. acknowledges partial support from NSF PAARE grant AST-1358862. This work has made use of NASA's Astrophysics Data System, the Extrasolar Planet Encyclopedia, the NASA Exoplanet Archive, the SIMBAD database operated at CDS, Strasbourg, France, and the VizieR catalog access tool, CDS, Strasbourg, France. We make use of Filtergraph, an online data visualization tool developed at Vanderbilt University through the Vanderbilt Initiative in Data-intensive Astrophysics (VIDA). We also used data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles; the Jet Propulsion Laboratory/California Institute of Technology, which is funded by the National Aeronautics and Space Administration; the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation; and the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. MINERVA is a collaboration among the Harvard-Smithsonian Center for Astrophysics, Pennsylvania State University, the University of Montana, and the University of New South Wales. MINERVA is made possible by generous contributions from its collaborating institutions and the Mt. Cuba Astronomical Foundation, the David & Lucile Packard Foundation, National Aeronautics and Space Administration (EPSCOR grant NNX13AM97A), the Australian Research Council (LIEF grant LE140100050), and the National Science Foundation (grants 1516242 and 1608203). Note added in proof: During the preparation of this paper, our team became aware of another paper by The Multi-site All-Sky CAmeRA (MASCARA) Collaboration (Talens et al. 2017b) reporting the discovery of a planetary companion to the host star discussed here, HD 185603 (Talens et al. 2017a). While we assume that this planetary companion is indeed KELT-20b, no information about the analysis procedure or any results were shared between our groups prior to the submission of both papers. We would like to thank the MASCARA Collaboration for their collegiality and willingness to work with the KELT Collaboration to coordinate our announcements of these discoveries simultaneously.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Harvard Future Faculty Leaders Postdoctoral FellowshipUNSPECIFIED
NSF Graduate Research FellowshipDGE-1343012
Mt. Cuba Astronomical FoundationUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Australian Research CouncilLE140100050
Subject Keywords:methods: observational – planets and satellites: detection – planets and satellites: gaseous planets – stars: individual (HD 185603) – techniques: photometric – techniques: radial velocities
Issue or Number:5
Record Number:CaltechAUTHORS:20171019-080336913
Persistent URL:
Official Citation:Michael B. Lund et al 2017 AJ 154 194
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:82477
Deposited By: Tony Diaz
Deposited On:19 Oct 2017 16:16
Last Modified:03 Oct 2019 18:55

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