Evolution of the synthetic X-ray luminosity L_X (top panel) and temperature T_X (bottom panel) integrated over the energy range 0.3−2.0 keV versus T_eff (which increases with time) for the three different models HC (black diamonds), HC_H (red crosses), and HC (blue triangles). The observed position of the PN BD+30° 3639 with a WR-type CS is indicated by a black star for comparison.