Stellar Spin-Orbit Alignment for Kepler-9, a Multi-transiting Planetary system with Two Outer Planets Near 2:1 Resonance

摘要

We present spectroscopic measurements of the Rossiter-McLaughlin effect forthe planet b of Kepler-9 multi-transiting planet system. The resultingsky-projected spin-orbit angle is $\lambda=-13^{\circ} \pm 16^{\circ}$, whichfavors an aligned system and strongly disfavors highly misaligned, polar, andretrograde orbits. Including Kepler-9, there are now a total of 4Rossiter-McLaughlin effect measurements for multiplanet systems, all of whichare consistent with spin-orbit alignment.