HAT-P-24b: An inflated hot-Jupiter on a 3.36d period transiting a hot, metal-poor star

TL;DR

HAT-P-24b is an inflated hot Jupiter orbiting a metal-poor star with a 3.36-day period, and the study provides detailed system parameters, robustness checks of fitting techniques, and insights into its orbital eccentricity and spin-orbit alignment.

Contribution

This paper reports the discovery and detailed characterization of HAT-P-24b, including analysis of fitting techniques and orbital properties, which enhances understanding of hot Jupiter systems.

Findings

HAT-P-24b has a mass of 0.681 MJ and radius of 1.243 RJ.

The planet likely has a small eccentricity of about 0.052.

The Rossiter-McLaughlin effect amplitude is estimated at 95 m/s.

Abstract

We report the discovery of HAT-P-24b, a transiting extrasolar planet orbiting the moderately bright V=11.818 F8 dwarf star GSC 0774-01441, with a period P = 3.3552464 +/- 0.0000071 d, transit epoch Tc = 2455216.97669 +/- 0.00024 (BJD_UTC), and transit duration 3.653 +/- 0.025 hours. The host star has a mass of 1.191 +/- 0.042 Msun, radius of 1.317 +/- 0.068 Rsun, effective temperature 6373 +/- 80 K, and a low metallicity of [Fe/H] = -0.16 +/- 0.08. The planetary companion has a mass of 0.681 +/- 0.031 MJ, and radius of 1.243 +/- 0.072 RJ yielding a mean density of 0.439 +/- 0.069 g cm-3 . By repeating our global fits with different parameter sets, we have performed a critical investigation of the fitting techniques used for previous HAT planetary discoveries. We find that the system properties are robust against the choice of priors. The effects of fixed versus fitted limb darkening are also examined. HAT-P-24b probably maintains a small eccentricity of e = 0.052 +0.022 -0.017, which is accepted over the circular orbit model with false alarm probability 5.8%. In the absence of eccentricity pumping, this result suggests HAT-P-24b experiences less tidal dissipation than Jupiter. Due to relatively rapid stellar rotation, we estimate that HAT-P-24b should exhibit one of the largest known Rossiter-McLaughlin effect amplitudes for an exoplanet (deltaVRM ~ 95 m/s) and thus a precise measurement of the sky-projected spin-orbit alignment should be possible.