Orbital period (in logarithmic scale) vs. white-dwarf temperature for the systems in Table 2. Filled symbols mark PCEBs with multiple Hα emission components, open symbols those with single components. The shape of the symbol indicates the type of emission from the secondary star: irradiation (triangle), activity (square), or yet unknown (circle). J1559 is marked by a star, since it probably presents both effects. Objects that show non-LTE effects are indicated by crosses. The plot does not include the systems J0303 (T_WD unknown) and J1411 (uncertain number of emission components).