Skip to main content# A Bayesian Analysis of Light Curves for 783 Kepler (Near)Contact Binary Stars: Extreme-Mass-Ratio Systems and a New Mass Ratio versus Period Lower Limit

Presentation #308.06 in the session Binaries at Different Evolutionary Stages.

Published onJun 29, 2022

A Bayesian Analysis of Light Curves for 783 Kepler (Near)Contact Binary Stars: Extreme-Mass-Ratio Systems and a New Mass Ratio versus Period Lower Limit

Contact binary star systems are the most common type of eclipsing binary. Their evolution culminates with merger, producing a luminous red nova, of which V1309 Sco is the prototype. Detailed studies of large populations are now possible, shedding light on the evolutionary pathways of close binaries. We present a Bayesian light curve analysis of 783 candidate contact binaries drawn from the Kepler catalog of close binaries having periods 0.2-2.0 days and light curve morphology consistent with contact or near-contact systems. We tabulate probabilistic system inclinations, fillout factors, mass ratios, third-light fractions, and ratio of component temperatures T2/T1 for these systems. At the exquisite precision of the Kepler measurements, all systems display light curves inconsistent with the basic five-parameter models — real physical features such as spots are ubiquitous at levels that are large relative to the photometric precision. Nevertheless, the Bayesian analysis yields good constraints on all the primary system parameters in the majority of cases. We find that true contact systems are rare at periods P>0.7 days. The distribution of mass ratio versus orbital period shows a distinct lower limit near q=M2/M1~0.1, consistent with revised theoretical predictions (Molnar et al. at this meeting) that the onset of a Darwin instability rapidly instigates a merger once systems reach these extreme mass ratios. These results are consistent with a predicted limiting mass ratio that varies with orbital period from q~0.05 for P<0.8 d, rising to q~0.15 for P>1.2 d. We also identify a dearth of q>0.7 systems, supporting the additional prediction that a previously unidentified instability precipitates rapid mass exchange when high mass ratio systems first come into contact, persisting until the mass ratio is below the instability limit. Implications for binary evolution pathways are discussed.