Map of the projected merit function (in a log scale) along the log q(core) – X_core(C+O) plane. At each log q(core), X_core(C+O) position, the value given is the minimum of log S² that can be found among the values obtained for all M_∗ and log q(H). The best-fit model is indicated by an asterisk, while the model corresponding to the second minimum of the merit function is indicated by a cross. White contours show regions where the frequency fits have S² values within the 1σ, 2σ, and 3σ confidence levels relative to the best-fit solution.