Distribution of the sample in the N against He abundance plane (cf. Fig. 1 in Martínez-Sebastián et al. 2025). The gray area marks the region covered by Ekström et al. (2012) models for 20–60 M_⊙ and v_ini/v_crit = 0.2–0.4 during the main sequence; the light brown area indicates CAS values from Nieva & Przybilla (2012). Symbols are the same as in Fig. 1; red crosses in the background mark SB1 systems. Vertical dotted lines mark the He low and rich limits (Y_He ≤ 0.08 and Y_He > 0.12); the horizontal dotted line separates N-low stars. In the upper X-axis, He is shown by mass; in the lower X-axis, He is shown by number.