Presentation #501.05 in the session Architectures 2.
Observing the Rossiter-McLaughlin effect during a planetary transit allows the determination of the angle λ between the sky projections of the star’s spin axis and the planet’s orbital axis. Such observations have revealed a large population of well-aligned systems and a smaller population of misaligned systems, with values of λ ranging up to 180 degrees. For a subset of 57 systems, we can now go beyond the sky projection and determine the 3-d obliquity Ψ by combining the Rossiter-McLaughlin data with constraints on the line-of-sight inclination of the spin axis. Here we show that the misaligned systems do not span the full range of obliquities; they show a preference for nearly-perpendicular orbits (Ψ = 80–125 degrees) that seems unlikely to be a statistical fluke. If confirmed by further observations, this pile-up of polar orbits is a clue about the unknown processes of obliquity excitation and evolution (Albrecht et al. 2021, ApJ Letters, 916:L1).