Distribution of [Zr/Fe] vs. [Nb/Fe] for our target stars. Abundances of intrinsic S stars and M stars are from Neyskens et al. (2015). The abundances of extrinsic S stars and barium stars are from this work. The open blue squares refer to the four N-enriched barium stars (HD 43389, HD 60197, HD 100503, and HD 121447 in order of increasing value of [Nb/Fe]). HD 28159, a star previously known as K0III and which proved to be slightly enriched in s-process (see Sect. 7.1) is located at ([Nb/Fe], [Zr/Fe]) = (0.43, 0.30). The magenta shaded band indicates the expected location of stars polluted by material resulting from the s-process operating at temperatures between 1.0 (upper line) and 3.0×10⁸ K (lower line). These simple predictions assume that the chain of neutron captures along the Zr isotopes is in local equilibrium.