KELT-7b: A HOT JUPITER TRANSITING A BRIGHT V = 8.54 RAPIDLY ROTATING F-STAR

Abstract

We report the discovery of KELT-7b, a transiting hot Jupiter with a mass of 1.28 ± 0.18 M[subscript J], radius of 1.533[+0.046 over -0.047] R[subscript 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[subscript eff] = 6789[+50 over -49] K, [Fe/H] = 0.139[+0.075 over -0.081], and log g = 4.149 ± 0.019]. It has a mass of 1.535 [+0.066 over -0.054] M[subscript ⊙], a radius of 1.732[+0.043 over -0.045] R[subscript ⊙], 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[superscript −1]) results in a Rossiter–McLaughlin effect with an unusually large amplitude of several hundred m s[superscript −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[° over .]7 ± 5[° over .]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.