Parameter space of T_eff and log(L/L_⊙), which we used for the determination of τ_c by matching them with the Yale-Potsdam Stellar Isochrones. The gray circles are the stars of our sample. The τ_c isocontours are shown as solid colored lines. The red dashed lines mark the ZAMS and TAMS. The stellar mass from 0.4 M_⊙ to 2 M_⊙ are marked at the beginning of each isochrone. The typical uncertainty for the solar mass is plotted at the bottom. Note the isochrones are plotted at metallicilty [Fe/H] = 0.