PF-02-0035

How often do planets form misaligned with their host stars?

Matthew J. Fields, Andrew W. Mann, Jonathan L. Bush, Aurora Y. Kesseli

Over the last few decades, many planetary systems have been discovered misaligned, i.e., the planetary orbital axis is offset from the stellar spin axis. We assume misalignments result from dynamical processes that occur after the formation of the planets. However, it is possible for protoplanetary disks to become quickly misaligned from their hosts due to the presence of wide binary companions, close stellar flybys, and/or localized turbulence within the star-forming cloud. This could happen during the planet-formation process, raising the question: how often do planets form misaligned with their host stars? We aim to characterize the occurrence of disk-star misalignments by deriving statistical alignment distributions for populations of young stars with resolved disks from the Atacama Large Millimeter/submillimeter Array (ALMA). Here, we present several validations of our method to derive the inclination angle of the stellar spin axis, including homogeneously-derived projected rotation velocities, rotation periods, and radii for a sample of ~20 pre-main-sequence systems. We also show how, using a hierarchical Bayesian model, one can extract the statistical alignment distribution from these measurements. With such a model, we will determine the systematic errors of our model framework and account for these systematic effects when we apply our method to real disk-bearing systems.