KELT-21b: A Hot Jupiter Transiting the Rapidly Rotating Metal-poor Late-A Primary of a Likely Hierarchical Triple System

Johnson, Marshall C. and Rodriguez, Joseph E. and Zhou, George ORCID: and Gonzales, Erica J. and Cargile, Phillip A. and Crepp, Justin R. and Penev, Kaloyan and Stassun, Keivan G. and Gaudi, B. Scott and Colon, Knicole D. and Stevens, Daniel J. and Strassmeier, Klaus G. and Ilyin, Ilya and Collins, Karen A. and Kielkopf, John F. and Oberst, Thomas E. and Maritch, Luke and Reed, Phillip A. and Gregorio, Joao and Bozza, Valerio and Calchi Novati, Sebastiano and D'Ago, Giuseppe and Scarpetta, Gaetano and Zambelli, Roberto and Latham, David W. and Bieryla, Allyson and Cochran, William D. and Endl, Michael and Tayar, Jamie and Serenelli, Aldo and Aguirre, Victor Silva and Clarke, Seth P. and Martinez, Maria and Spencer, Michelle and Trump, Jason and Joner, Michael D. and Bugg, Adam G. and Hintz, Eric G. and Stephens, Denise C. and Arredondo, Anicia and Benzaid, Anissa and Yazdi, Sormeh and McLeod, Kim K. and Jensen, Eric L. N. and Hancock, Daniel A. and Sorber, Rebecca L. and Kasper, David H. and Jang-Condell, Hannah and Beatty, Thomas G. and Carroll, Thorsten and Eastman, Jason and James, David and Kuhn, Rudolf B. and Labadie-Bartz, Jonathan and Lund, Michael B. and Mallonn, Matthias and Pepper, Joshua and Siverd, Robert J. and Yao, Xinyu and Cohen, David H. and Curtis, Ivan A. and DePoy, D. L. and Fulton, Benjamin J. and Penny, Matthew T. and Relles, Howard and Stockdale, Christopher and Tan, Thiam-Guan and Villanueva, Steven, Jr. (2018) KELT-21b: A Hot Jupiter Transiting the Rapidly Rotating Metal-poor Late-A Primary of a Likely Hierarchical Triple System. The Astronomical Journal, 155 (2):100. pp. 1-20. ISSN 0004-6256

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We present the discovery of KELT-21b, a hot Jupiter transiting the V = 10.5 A8V star HD 332124. The planet has an orbital period of P = 3.6127647 ± 0.0000033 days and a radius of 1.586-0.040+0.039 RJ. We set an upper limit on the planetary mass of at confidence. We confirmed the planetary nature of the transiting companion using this mass limit and Doppler tomographic observations to verify that the companion transits HD 332124. These data also demonstrate that the planetary orbit is well-aligned with the stellar spin, with a sky-projected spin-orbit misalignment of λ = -5.6-1.91.7. The star has Teff = 7598-8481 K, Mz.ast; = 1.458-0.028+0.029 M⊙, Rz.ast; = 1.638 ± 0.034 R⊙ and v sin I∗ = 146 km s-1, the highest projected rotation velocity of any star known to host a transiting hot Jupiter. The star also appears to be somewhat metal poor and α-enhanced, with [Fe/H] = -405-0.033+0.032 and [α/Fe] = 0.145 ± 0.053; these abundances are unusual, but not extraordinary, for a young star with thin-disk kinematics like KELT-21. High-resolution imaging observations revealed the presence of a pair of stellar companions to KELT-21, located at a separation of 1.″2 and with a combined contrast of ΔKs = 6.39 ± 0.06 with respect to the primary. Although these companions are most likely physically associated with KELT-21, we cannot confirm this with our current data. If associated, the candidate companions KELT-21 B and C would each have masses of ∼0.12 M⊙, a projected mutual separation of ∼20 au, and a projected separation of ∼500 au from KELT-21. KELT-21b may be one of only a handful of known transiting planets in hierarchical triple stellar systems.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 08 Feb 2022 03:44
Last Modified: 04 Apr 2022 08:03
Uncontrolled Keywords: methods: observational; planets and satellites: detection; planets and satellites: gaseous planets; stars: individual (HD 332124); techniques: photometric; techniques: radial velocities; Astrophysics - Earth and Planetary Astrophysics; Astrophysics - Astrophysics of Galaxies
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
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