Maximum S/N versus entropy of the background-normalized PDS for 3212 observed red-giant stars, with the y axis plotted on a logarithmic scale. Known binary stars are shown as gray circle (see Sect. 2 for more details of this set of stars). The panels on the right show the background-normalized PDSs corresponding to specific red symbols marked on the left panel. These PDS figures highlight the characteristics associated with their different entropy levels.