* Astronomy

Title: KELT-7b: A hot Jupiter transiting a bright V=8.54 rapidly rotating F-star
Author: Allyson Bieryla, Karen Collins, Thomas G. Beatty, Jason Eastman, Robert J. Siverd, Joshua Pepper, B. Scott Gaudi, Keivan G. Stassun, Caleb Canas, David W. Latham, Lars A. Buchhave, Roberto Sanchis-Ojeda, Joshua N. Winn, Eric L. N. Jensen, John F. Kielkopf, Kim K. McLeod, Joao Gregorio, Knicole D. Colon, Rachel Street, Rachel Ross, Matthew Penny, Samuel N. Mellon, Thomas E. Oberst, Benjamin J. Fulton, Ji Wang, Perry Berlind, Michael L. Calkins, Gilbert A. Esquerdo, Darren L. DePoy, Andrew Gould, Jennifer Marshall, Richard Pogge, Mark Trueblood, Patricia Trueblood

We report the discovery of KELT-7b, a transiting hot Jupiter with a mass of 1.28±0.18 MJ, radius of 1.53+0.046-0.047 RJ, and an orbital period of 2.7347749±0.0000039 days. The bright host star (HD33643; KELT-7) is an F-star with V=8.54, Teff =6789+50-49 K, [Fe/H] =0.139+0.075-0.081, and logg=4.149±0.019. It has a mass of 1.535+0.066-0.054 Msun, a radius of 1.732+0.043-0.045 Rsun, and is the fifth most massive, fifth hottest, and the ninth brightest star known to host a transiting planet. It is also the brightest star around which KELT has discovered a transiting planet. Thus, KELT-7b is an ideal target for detailed characterisation given its relatively low surface gravity, high equilibrium temperature, and bright host star. The rapid rotation of the star (73±0.5 km/s) results in a Rossiter-McLaughlin effect with an unusually large amplitude of several hundred m/s. We find that the orbit normal of the planet is likely to be well-aligned with the stellar spin axis, with a projected spin-orbit alignment of \lambda=9.7±5.2 degrees. This is currently the most rapidly rotating star to have a reflex signal (and thus mass determination) due to a planetary companion measured.

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