Talk

Refining Stellar Rotation Periods by Double-Dipping

Gibor Basri, UC Berkeley

The age of precision space-based light curves has vastly increased the number of rotation periods known for main sequence stars. The primary reference for more than 30,000 rotation periods from the Kepler Prime mission has been McQuillan et al (2013). They utilized an autocorrelation (AC) technique, whose results have largely been agreed with by many other analyses and methodologies. The primary uncertainty in the AC method occurs because stars sometimes exhibit two dips per rotation and sometimes only one. Basri & Nguyen (2017) found that this behavior is systematic with stellar rotation period and stellar temperature (more rapid rotators exhibit more single-dip behavior). We examine whether this issue introduces a systematic error in the AC method (and others with similar results). About 8% of the McQuillan periods are double what they should be, mostly for periods greater than about 20 days. We present a refined method for determining rotation periods which also utilizes the distribution of light curve dip durations, and discuss the criteria by which we determine whether the autocorrelation method finds the right value.