We present the discovery of KELT-24 b, a massive hot Jupiter orbiting a bright (V = 8.3 mag, K = 7.2 mag) young F-star with a period of 5.6 days. The host star, KELT-24 (HD 93148), has a Teff = 6509-+4950 K, a mass of M* = 1.460-+0.0590.055 Me, a radius of R* = 1.506 ± 0.022 Re, and an age of 0.78-+0.420.61 Gyr. Its planetary companion (KELT-24 b) has a radius of RP = 1.272 ± 0.021 RJ and a mass of MP = 5.18-+0.220.21 MJ, and from Doppler tomographic observations, we find that the planet’s orbit is well-aligned to its host star’s projected spin axis (l = 2.6-+3.65.1). The young age estimated for KELT-24 suggests that it only recently started to evolve from the zero-age main sequence. KELT-24 is the brightest star known to host a transiting giant planet with a period between 5 and 10 days. Although the circularization timescale is much longer than the age of the system, we do not detect a large eccentricity or significant misalignment that is expected from dynamical migration. The brightness of its host star and its moderate surface gravity make KELT-24b an intriguing target for detailed atmospheric characterization through spectroscopic emission measurements since it would bridge the current literature results that have primarily focused on lower mass hot Jupiters and a few brown dwarfs.
Bibliographical noteFunding Information:
We thank Laura Kreidberg, Andrew Vanderburg, and James Kirk for their valuable discussions and insight. J.E.R. was supported by the Harvard Future Faculty Leaders Postdoctoral fellowship. Work by G.Z. is provided by NASA through Hubble Fellowship grant HST-HF2-51402.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. K.G.S. acknowledges support from the Vanderbilt Office of the Provost through the Vanderbilt Initiative in Data-intensive Astrophysics. T.N and A.Y. are also grateful to Mizuki Isogai, Akira Arai, and Hideyo Kawakita for their technical support on observations at Koyama Astronomical Observatory. This work is partly supported by JSPS KAKENHI grant Numbers JP18H01265 and JP18H05439, and JST PRESTO grant No. JPMJPR1775. J.L.-B. acknowledges support from FAPESP (grant 2017/ 23731-1). K.P. acknowledges support from NASA grants 80NSSC18K1009 and NNX17AB94G.
The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium.
The ASAS-SN observations are used to help vet exoplanet candidates from KELT. ASAS-SN would like to thank Las Cumbres Observatory and its staff for their continued support. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University, NSF grant AST-1515927, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and Astro-Particle Physics (CCAPP) at OSU, the Chinese Academy of Sciences South America Center for Astronomy (CASSACA), and the Villum Fonden (Denmark).
This work makes use of observations from the LCOGT network. This research has made use of SAO/NASA’s Astrophysics Data System Bibliographic Services. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. This work has made use of data from the European Space Agency (ESA) mission Gaia (https:// www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC,https://www. cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular, the institutions participating in the Gaia Multilateral Agreement. This work makes use of observations from the LCO network. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.
MINERVA is a collaboration among the Harvard-Smithsonian Center for Astrophysics, The Pennsylvania State University, the University of Montana, and the University of Southern Queensland. MINERVA is made possible by generous contributions from its collaborating institutions and 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). Any opinions, findings, and conclusions or recommendations expressed are those of the author and do not necessarily reflect the views of the National Science Foundation. Funding for MINERVA data-analysis software development is provided through a subaward under NASA award MT-13-EPSCoR-0011.
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