Coupling coefficient (q) at ν_max versus ν_max in the RC. The colour scale shows the stellar mass. The points are observed coupling and Δν and the tracks are from modelled stars. From left to right, top to bottom, the model [Fe/H] are −0.5, 0.0, 0.25, and 0.4. Similarly, the ranges for the observed [Fe/H] are −0.75 ≤ [Fe/H] ≤ −0.25, −0.25 ≤ [Fe/H] ≤ 0.125, 0.125 ≤ [Fe/H] ≤ 0.325, 0.325 ≤ [Fe/H].