Figure 27: Abundance ratios (by mass) N/C for He-WD (the solid line) and He-star donors (the
shaded region with dashed lines) as a function of the orbital period. For the helium star donors we
indicate the upper part of the full range of abundances which extends to 0. The dashed lines are
examples of tracks shown in detail in Figure 26. The helium white dwarfs are descendants of 1,
1.5 and stars (top to bottom). Image reproduced with permission from Figure 11 of [521],
copyright by the authors.