Period–eccentricity diagram for the M07 sample of binary giants in open clusters (open black squares), barium stars (small open blue circles), and blue-straggler binaries from the cluster NGC 188 (large filled blue dots; Gosnell et al. 2015). M07 cluster giant stars whose s-process abundances were derived are identified by red symbols: stars with normal s-process abundances are shown as crossed squares, and stars with enhanced s-process abundances are shown as circled squares, to be compared with the location of barium stars. The green solid line is the same envelope as that shown in Fig. 4 (see also Eq. (3)).