The light-curve intrinsic variability in 47 Kepler contact binary stars

This work studies the significance of light-curve intrinsic variability in the numerical modelling of contact binaries. Using synthetic light curves, we show that the starspot-based intrinsic variability increases the apparent mass ratio by Delta q = 5 per cent. For systems with orbital period P > 0.3 d, the effects of intrinsic variability averaged over a long time are compensated by Kepler-mission-like phase smearing. Further, we analyse 47 totally eclipsing Kepler mission contact binaries. We find a sharp cut-off of the intrinsic variability at P = 0.45 d. With light-curve numerical modelling and observational relations, we derive the physical parameters of 47 systems. At least 53 per cent of binaries have a possible third companion. 21 binaries show the O'Connell effect in the averaged phase curve. 19 of them have a primary maximum lower than the secondary, suggesting a stationary dark region on the trailing side. Using the P = 0.45 d cut-off, we propose a new approach to the period-colour relation. The only parameter correlating with the magnitude of the intrinsic variability is the apparent effective temperature ratio. We conclude that, instead of describing the system parameters, the A/W subtype division should be applicable only to the light curves, as a tentative phenomenon.