Helium abundance Y versus metallicity Z (left panels), and stellar mass versus Age (right panels) for stars listed in C06. Circles and triangles represent stars with ages younger and older than 13.5 Gyr, respectively. The Sun’s properties (Z = 0.0167, Y = 0.262, Age = 4.6 Gyr, and M = 1   M_⊙) are represented by the symbol of the Sun. Open and filled symbols are the extrapolated and interpolated results, respectively. The dotted line represents the reference Y–Z relation Y = 0.240 + 2.0 × Z. Upper panels: FSPs determined using the method from C07. Middle panels: FSPs determined using the method proposed in this paper. Lower panels: similar to the middle panels, except theoretical evolutionary tracks have a variable [α/Fe] value (see text for more details).