T_eff − log ₁₀g probability distribution of all stars in our simulation computed with model set A. Darker colours indicate regions of higher probability. The grey solid and magenta dotted lines show the isochrones computed with detailed stellar-evolution models at 10 Gyr and 13.7 Gyr, respectively. The isochrones computed for the same ages with a detailed model that includes gravitational settling are shown as light-blue dashed and blue dot-dashed lines, respectively. The black dotted lines indicate the ranges of T_eff and log ₁₀g in which Lee et al. (2013) select the SEGUE stars. Black circles indicate all SEGUE stars with −2.4 ≤ [Fe/H] < − 2.2.