2015AJ....150...12B

We report the discovery of KELT-7b, a transiting hot Jupiter with a mass of 1.28 ± 0.18 M_J, radius of 1.533_–0.047^+0.046 R_J, and an orbital period of 2.7347749± 0.00000039 days. The bright host star (HD 33643; KELT-7) is an F-star with V = 8.54, T_eff= 6789_–49⁺⁵⁰ K, [Fe/H] = 0.139_–0.081^+0.075, and log g = 4.149 ± 0.019. It has a mass of 1.535_–0.054^+0.066 M_☉, a radius of 1.732_–0.045^+0.043 R_☉, and is the fifth most massive, fifth hottest, and the ninth brightest star known to host a transiting planet. It is also the brightest star around which Kilodegree Extremely Little Telescope (KELT) has discovered a transiting planet. Thus, KELT-7b is an ideal target for detailed characterization given its relatively low surface gravity, high equilibrium temperature, and bright host star. The rapid rotation of the star (73± 0.5 km/s) results in a Rossiter-McLaughlin effect with an unusually large amplitude of several hundred m/s. We find that the orbit normal of the planet is likely to be well-aligned with the stellar spin axis, with a projected spin-orbit alignment of λ = 9.°7±5.°2. This is currently the second most rapidly rotating star to have a reflex signal (and thus mass determination) due to a planetary companion measured.