Top panels. Isochrones with different contents of helium, carbon, nitrogen, and oxygen in the H_E vs. Y_E − H_E (left) and H_E vs. I_E − J_E (right) CMDs. The right panel shows the ChM for the M-dwarfs highlighted in the insets of the left and middle panels. All isochrones in the top panels have [Fe/H]=−1.5 with the exception of the isochrones I 6, which are enhanced in iron abundance by 0.1 dex with respect to the other isochrones. Bottom panels represent the H_E vs. Y_E − H_E (left) and H_E vs. I_E − Y_E (right) CMDs, and the ChM derived from these CMDs for the M-dwarfs plotted in the CMD insets (right). The isochrones I1–I5 in the bottom panels share the same iron to hydrogen ratios, [Fe/H]=−0.75, while isochrones I6 have [Fe/H]=−0.65.