Abstract
Stellar obliquity---the angle between a star's rotation axis and the orbital angular momentum vector of its planets---provides valuable insight into the formation and evolutionary history of planetary systems. However, it is unclear whether the origin of observed stellar obliquities is primordial (i.e., inherited from the protoplanetary disk) or generated by dynamical processes after the epoch of planet formation. We present the first comprehensive analysis of primordial stellar obliquities from an exhaustive compilation of young disk-bearing stars with resolved submillimeter imaging from ALMA together with new stellar inclination constraints using projected rotational velocities and stellar rotation periods. We find that modest levels of misalignment are common, which is consistent with a scenario of late anisotropic infall and delivery of a distinct source of angular momentum to the outer disk, perhaps along accretion streamers. These results contextualize the observed spin-orbit orientations of planetary systems, including the Solar System.
