HAT-P-24b: AN INFLATED HOT JUPITER ON A 3.36 DAY PERIOD TRANSITING A HOT, METAL-POOR STAR

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 days, transit epoch T c = 2455216.97669 ± 0.00024 (BJD)11, and transit duration 3.653 ± 0.025 hr. The host star has a mass of 1.191 ± 0.042 M ☉ , radius of 1.317 ± 0.068 R ☉ , 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 M J and radius of 1.243 ± 0.072 R J 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 Hungarian-made Automated Telescope 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 that 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 (Δ V RM ≃ 95 m s −1 ) and thus a precise measurement of the sky-projected spin–orbit alignment should be possible.