Circularization timescale vs. orbital period in binary star systems. The black, red, blue, and green curves denote different laws of fast-tide suppression effects: in absence of suppression, and with linear, 5/3, and square laws, respectively. The horizontal dashed lines from bottom to top denote one-third of the age of the four open clusters from young to old: M 35 of 150 Myr, M 67 of 4 Gyr, NGC 188 of 7 Gyr, and Halo of 10 Gyr.