Heavy-element enhancement diagnostic. Top panel: [Eu/Ba] versus [Fe/H] diagram for the four reference GCs. The Solar System r-process region is highlighted by the orange strip for [Eu/Ba] = +0.60 ± 0.13 (see text). Middle panel: [Zr/Ba] versus [Y/Ba] diagram for the three reference GCs that have Zr, Y, and Ba abundance determinations. The main r-process stars region is represented with the red-square (3 − σ). Bottom panel: [Ba/Eu] versus [Eu/Fe] diagram for the selected r-rich stars from the upper panel (see text). The light green region represents the regime of enhancement by both the r- and s-processes. The cyan and magenta regions show the domains of mainly r-process enhancement. The dot and cross colour code is the same as in Fig. 8.