Obliquity Measurements of Warm Jupiters around Early-type Stars

Long period planets provide tests for mechanisms that induce primordial misalignment in planetary systems. Star-planet tidal interactions are too weak to modify the orbital obliquity at these orbital distances. We report on two new warm Jupiter systems with obliquity measurements around rapidly rotating, hot host stars (T_eff > 6500 K). The first planet is a 22d warm Jupiter orbiting an F-star in a near circular orbit while the second system hosts a 17d warm Jupiter in an eccentric orbit around an A-star. In both of these systems, the spin-orbit angles are well-aligned. Changes to the spin axes of early-type stars will lead to an apparent spin-orbit misalignment, potentially contributing to the temperature-obliquity gradient seen in the hot Jupiter population. Most proposed mechanisms of misalignment do not have a strong dependence on the host star properties beyond planet-star tidal interactions. There is a paucity of warm Jupiters orbiting hot host stars that have an obliquity measurement. Increasing the obliquity measurements in this parameter space will help test these predictions and motivates full characterization of planets in long period orbits about early-type stars.