Eccentricity as a function of period for BiCeps in standard models (magenta) and control models (black). The thick lines show the mean eccentricity for given period, and the coloured areas represent the interquartile range. The figure quantitatively shows the boost of eccentricity for Cepheids which are subjected to cluster dynamics. The mean eccentricity at time t₀ (identical for both models) is shown by the yellow line.