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Abstract

As new exoplanetary systems have been discovered, it has become clear that our Solar System’s architecture is not the only possible result of planetary system formation, and, in fact, may not be the dominant architecture for systems with otherwise similar characteristics. One key difference is the angle between the stellar axis of rotation and the orbital axis of the planet(s) around a star: the stellar obliquity. Stellar obliquities ranging from 0◦ to 180◦ have been observed. This is different than what might be expected based upon the Sun, which is aligned with the planets to within 6◦. The exoplanetary systems whose obliquities have been previously measured tend to be those with giant close-in planets, because the signals in those cases are larger and easier to detect. As a result, very few investigations have been done into the obliquities of Kepler planet-hosting stars. Using a new control sample of stars and data from the California-Kepler Survey, we seek to fill in this gap in understanding and investigate the obliquity distribution of Kepler planet hosts. We analyzed the observed distribution of projected rotation velocity (v sin i) of the planet hosts and the control stars, finding that the hosts have typical inclinations of 60◦ to 70◦, corresponding to minimum obliquities of 20◦ to 30◦. These results suggest that planet-hosts were misaligned with the protoplanetary disk or later misaligned by dynamical heating.