Kippenhahn diagrams showing the proto-WD phase for the same systems as in Fig. 2. The plots show cross sections of the outer ~ 0.01 M_⊙ envelope of the proto-WD in mass coordinates, along the y-axis, as a function of stellar age on the x-axis (relative to the ZAMS age). The green areas denote zones with convection; the dotted white lines define lines of constant hydrogen abundance, 10^-2 to 10^-5 (from top to bottom). The intensity of the blue and red colour indicates the hydrogen abundance by mass fraction, as shown on the colour scale to the right. As a result of different input physics, the proto-WDs have slightly different masses and ages. See text for details.