Curvature 10³ α_obs as a function of n_max = ν_max/Δν. The thick line corresponds to the fit in established for red giants, and the dotted line to its extrapolation towards larger n_max. The dashed line provides an acceptable fit in valid for main-sequence stars. Error bars indicate the typical 1-σ uncertainties in three different domains. The color code of the symbols provides an estimate of the stellar mass; the colors of the lines correspond to the different regimes.