KELT-7b: A Hot Jupiter Transiting a Bright V = 8.54 Rapidly Rotating F-Star

We report the discovery of KELT-7b, a transiting hot Jupiter with a mass of 1.28 ± 0.18 MJ, radius of 1.533^(+0.046)_(-0.047) R_J, and an orbital period of 2.7347749 ± 0.0000039 days. The bright host star (HD 33643; KELT-7) is an F-star with V = 8.54, T_(eff) = 6789^(+50)_(-49)K, [Fe/H] = 0.139^(+0.075)_(-0.081), and log g = 4.149 ± 0.019. It has a mass of 1.535^(+0.066)_(-0. 054) M⊙, a radius of 1.732^(+0.043)_(-0.045) 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^(−1)) results in a Rossiter–McLaughlin effect with an unusually large amplitude of several hundred m s−1. 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