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 ^ { +50 } _ { -49 } K , a mass of M _ { * } = 1.460 ^ { +0.055 } _ { -0.059 } M _ { \odot } , radius of R _ { * } = 1.506 \pm 0.022 R _ { \odot } , and an age of 0.78 ^ { +0.61 } _ { -0.42 } Gyr .
Its planetary companion ( KELT-24 b ) has a radius of R _ { P } = 1.272 \pm 0.021 R _ { J } , a mass of M _ { P } = 5.18 ^ { +0.21 } _ { -0.22 } 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 ^ { +5.1 } _ { -3.6 } ) .
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 .