Distribution of [hs/ls] as a function of metallicity for the intrinsic S stars of our study (filled squares). The hs-index has been calculated using Ba and Nd, and the ls-index using Y and Zr. The symbols are color-coded with respect to the initial mass in the bins M_ini < 1.5 M_⊙ (blue), 1.5 ≤ M_ini < 2.5 M_⊙ (red), and M_ini ≥ 2.5 M_⊙ (green). We note that these mass bins are designed to match the [hs/ls] STAREVOL predictions only available for M_ini = 1.5, 2, 2.5 M_⊙. Open circles denote the predictions from pulse to pulse for the different initial masses.