The behavior of O - C curves for contact binaries in the Kepler catalog

Abstract

In this thesis, we study the timing of eclipses for contact binary systems in the Kepler catalog. Observed eclipse times were determined from Kepler long-cadence light curves and "observed minus calculated" (0 - C) curves were generated for both primary and secondary eclipses of the contact binary systems. We found the 0 - C curves of contact binaries to be clearly distinctive from the curves of other binaries. The key characteristics of these curves are random-walk like variations, with typical semi-amplitudes of 200 to 300 seconds, quasi-periodicities, and anti-correlated behavior between the curves of the primary and secondary eclipses. We performed a formal analysis of systems with dominant anti-correlated behavior, calculating correlation coefficients as low as -0.77, with a mean value of -0.42. We dismiss several physical explanations to account for the observed the anti-correlation of the 0 - C curves. Instead, we propose a simple geometric model of a starspot that is continuously visible around the orbit.