KELT-24b: A 5M J Planet on a 5.6 day Well-aligned Orbit around the Young V = 8.3 F-star HD 93148

Abstract

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-circle dot, a radius of R-* = 1.506 +/- 0.022 R-circle dot, 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.