Upper panel: [Zr/Fe] abundance ratios as a function of the metallicity for the five sample stars, compared with literature abundances. Symbols are the same as in Figs. 8. Lower panel: [Zr/Ba] vs. [Fe/H] diagram for the sample stars and results from literature. Symbols are the same as in Figs. 8. The yellow and cyan regions correspond to the main r-process signature and the abundance ratio from metal-poor stars enhanced in the lightest heavy elements (see text for details).