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The Astronomical Journal


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 T eff = ${6509}_{-49}^{+50}$ K, a mass of M * = ${1.460}_{-0.059}^{+0.055}$ M ⊙, a radius of R * = 1.506 ± 0.022 R ⊙, and an age of ${0.78}_{-0.42}^{+0.61}$ Gyr. Its planetary companion (KELT-24 b) has a radius of R P = 1.272 ± 0.021 R J and a mass of M P = ${5.18}_{-0.22}^{+0.21}$ M J, and from Doppler tomographic observations, we find that the planet's orbit is well-aligned to its host star's projected spin axis ($\lambda ={2.6}_{-3.6}^{+5.1}$). 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.


This work is a preprint that is freely available courtesy of IOP Publishing and the American Astronomical Society. The final published version is available online.