Measurements of Stellar Inclinations for Kepler Planet Candidates Ii: Candidate Spin-orbit Misalignments in Single and Multiple-transiting Systems

We present a test for spin-orbit alignment for the host stars of 25 candidate planetary systems detected by the Kepler spacecraft. The inclination angle of each star’s rotation axis was estimated from its rotation period, rotational line broadening, and radius. The rotation periods were determined using the Kepler photometric time series. The rotational line broadening was determined from high-resolution optical spectra with Subaru/HDS. Those same spectra were used to determine the star’s photospheric parameters (effective temperature, surface gravity, metallicity) which were then interpreted with stellar-evolutionary models to determine stellar radii. We combine the new sample with the 7 stars from our previous work on this subject, finding that the stars show a statistical tendency to have inclinations near 90◦, in alignment with the planetary orbits. Possible spin-orbit misalignments are seen in several systems, including three multiple-planet systems (KOI-304, 988, 2261). Ideally these systems should be scrutinized with complementary techniques—such as the RossiterMcLaughlin effect, starspot-crossing anomalies or asteroseismology—but the measurements will be difficult owing to the relatively faint apparent magnitudes and small transit signals in these systems. Subject headings: planets and satellites: general – planets and satellites: formation – stars: rotation – techniques: spectroscopic