Measurements of mid-transit times from 206Kepler transits. The green filled circles are our selection of 21 low-χ² transits. The line represents a first-order polynomial fit to the error-weighted measurements. The lower panel shows the residuals with outliers cut-off; the variations are primarily caused by deformations of the transit due to starspots. The shaded area contains the transits that previously have been analyzed by Sanchis-Ojeda & Winn (2011). See Sects. 2.1 and 3.1 for detailed explanations.