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Description
We present the discovery of a hot Jupiter transiting the V=9.23mag main-sequence A-star KELT-17 (BD+14 1881). KELT-17b is a 1.31_-0.29_^+0.28^M_J_, 1.525_-0.060_^+0.065^R_J_ hot-Jupiter in a 3.08-day period orbit misaligned at -115.9{deg}+/-4.1{deg} to the rotation axis of the star. The planet is confirmed via both the detection of the radial velocity orbit, and the Doppler tomographic detection of the shadow of the planet during two transits. The nature of the spin-orbit misaligned transit geometry allows us to place a constraint on the level of differential rotation in the host star; we find that KELT-17 is consistent with both rigid-body rotation and solar differential rotation rates ({alpha}<0.30 at 2{sigma} significance). KELT-17 is only the fourth A-star with a confirmed transiting planet, and with a mass of 1.635_-0.061_^+0.066^M_{Sun}_, an effective temperature of 7454+/-49K, and a projected rotational velocity of vsinI_*_=44.2_-1.3_^+1.5^km/s; it is among the most massive, hottest, and most rapidly rotating of known planet hosts.
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