Stellar evolution of a binary corresponding to β Lyr A. The component radii R₁, R₂ vs. the primary mass M₁ are plotted (top), with observed values indicated by full circles, together with the distance a and R₁, R₂ vs. time t (middle); see horizontal dashed lines, and surface abundances X, Y, A_C12, A_O16 vs. time t (bottom). At t = 19.613 × 10⁶ yr, the mass ratio q corresponds to the observed one.