TOI-4641b: an aligned warm Jupiter orbiting a bright (V=7.5) rapidly rotating F-star

We report the discovery of TOI-4641b, a warm Jupiter transiting a rapidly rotating F-type star with a stellar effective temperature of 6560 K. The planet has a radius of 0.73 R-Jup, a mass smaller than 3.87 M-Jup(3 sigma), and a period of 22.09 d. It is orbiting a bright star (V=7.5 mag) on a circular orbit with a radius and mass of 1.73 R-circle dot and 1.41 M-circle dot. Follow-up ground-based photometry was obtained using the Tierras Observatory. Two transits were also observed with the Tillinghast Reflector Echelle Spectrograph, revealing the star to have a low projected spin-orbit angle (lambda=1.41-0.76+0.76 degrees). Such obliquity measurements for stars with warm Jupiters are relatively few, and may shed light on the formation of warm Jupiters. Among the known planets orbiting hot and rapidly rotating stars, TOI-4641b is one of the longest period planets to be thoroughly characterized. Unlike hot Jupiters around hot stars which are more often misaligned, the warm Jupiter TOI-4641b is found in a well-aligned orbit. Future exploration of this parameter space can add one more dimension to the star-planet orbital obliquity distribution that has been well sampled for hot Jupiters.