  Only a few hot Jupiters are known to orbit around fast rotating stars. These
exoplanets are harder to detect and characterize and may be less common than
around slow rotators. Here, we report the discovery of the transiting hot
Jupiter XO-6b, which orbits a bright, hot, and fast rotating star: V = 10.25,
Teff = 6720 +/- 100 K, v sin i = 48 +/- 3 km/s. We detected the planet from its
transits using the XO instruments and conducted a follow-up campaign. Because
of the fast stellar rotation, radial velocities taken along the orbit do not
yield the planet's mass with a high confidence level, but we secure a 3-sigma
upper limit Mp < 4.4 MJup. We also obtain high resolution spectroscopic
observations of the transit with the SOPHIE spectrograph at the 193-cm
telescope of the Observatoire de Haute-Provence and analyze the stellar lines
profile by Doppler tomography. The transit is clearly detected in the spectra.
The radii measured independently from the tomographic analysis and from the
photometric lightcurves are consistent, showing that the object detected by
both methods is the same and indeed transits in front of XO-6. We find that
XO-6b lies on a prograde and misaligned orbit with a sky-projected obliquity
lambda = -20.7 +/- 2.3 deg. The rotation period of the star is shorter than the
orbital period of the planet: Prot < 2.12 days, Porb = 3.77 days. Thus, this
system stands in a largely unexplored regime of dynamical interactions between
close-in giant planets and their host stars.
