Left : differences between observed and predicted eclipse times based on the ephemerides of Table A.2. The data for the deeper eclipse are shown by blue dots, and the data for the shallower eclipse are shown as red circles. Close-ups are provided for TYC 1881-933-1. Right : Fourier spectrum of the O − C values of the times of primary minimum of TYC 1881-933-1 (top panel) and the associated spectral window (bottom panel).