MEASUREMENTS OF STELLAR INCLINATIONS FOR<i>KEPLER</i>PLANET CANDIDATES. II. CANDIDATE SPIN-ORBIT MISALIGNMENTS IN SINGLE- AND MULTIPLE-TRANSITING SYSTEMS

Abstract

We present a test for spin-orbit alignment for the host stars of 25 candidate\nplanetary systems detected by the {\\it Kepler} spacecraft. The inclination\nangle of each star's rotation axis was estimated from its rotation period,\nrotational line broadening, and radius. The rotation periods were determined\nusing the {\\it Kepler} photometric time series. The rotational line broadening\nwas determined from high-resolution optical spectra with Subaru/HDS. Those same\nspectra were used to determine the star's photospheric parameters (effective\ntemperature, surface gravity, metallicity) which were then interpreted with\nstellar-evolutionary models to determine stellar radii. We combine the new\nsample with the 7 stars from our previous work on this subject, finding that\nthe stars show a statistical tendency to have inclinations near 90$^\\circ$, in\nalignment with the planetary orbits. Possible spin-orbit misalignments are seen\nin several systems, including three multiple-planet systems (KOI-304, 988,\n2261). Ideally these systems should be scrutinized with complementary\ntechniques---such as the Rossiter-McLaughlin effect, starspot-crossing\nanomalies or asteroseismology---but the measurements will be difficult owing to\nthe relatively faint apparent magnitudes and small transit signals in these\nsystems.\n