Stellar structure and oscillations of a 1.0 M_⊙ star from the single-star model (red) and a mass-donor model (black). Left panels: Profiles of the Lamb frequency, log S​_l = 1 (solid lines: left y axis), and the hydrogen mass fraction, X (dashed lines: right y axis), in the mass co-ordinates (x axis). Middle panels: Corresponding acoustic-model frequency separation ratios, r₀₁, r₁₀, and r₀₂ (squares, triangles, and circles), between small and large frequency separations, respectively, which are calculated with Equations (7). Right panels: Normalized large-frequency separation (Δν_l/⟨Δν_l⟩) (l = 0, 1, 2, corresponding to squares, triangles, and circles) as a function of radial order (n).