Evolutionary tracks for stars with 0.9 M_⊙ from the MS to the tip of the RGB. The left panel shows the effects produced by different metallicities (from left to right: Z = 1.6 × 10^-4, 1.6 × 10^-3, 5.03 × 10^-3, and 1.57 × 10^-2) with Y = 0.245. The effects produced by different helium abundances (Y = 0.245, 0.295, and 0.345) for two metallicities ([Fe/H] = −2.25, and −0.25) are shown in the right panel. In parentheses are labeled the age in Gyr at the RGB tip for each evolutionary track.