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K2-31b, a grazing transiting hot Jupiter on an 1.26-day orbit around a bright G7V star

We report the discovery of K2-31b, the first confirmed transiting hot Jupiter detected by the K2 space mission. We combined K2 photometry with FastCam lucky imaging and FIES and HARPS high-resolution spectroscopy to confirm the planetary nature of the transiting object and derived the system parameters. K2-31b is a 1.8-Jupiter-mass planet on an 1.26-day-orbit around a G7\,V star ($M_\star=0.91$~\Msun, $R_\star=0.78$~\Rsun). The planetary radius is poorly constrained (0.7$<$$R_\mathrm{p}$$<$1.4~\Rjup), owing to the grazing transit and the low sampling rate of the K2 photometry.