Helium against nitrogen abundances for the studied sample. Circles and crosses indicate Likely Single and binary stars, respectively, while identified runaway stars are highlighted by red symbols. Typical uncertainties in He and N abundances are marked with a gray error bar in the upper left corner. HD 226868 (optical counterpart of Cyg X-1) is surrounded by a green circle. Blue and gray shadowed strips delimit the locations of two published solar-abundance single-star-evolution tracks. Baseline abundances for these models are marked with a bluish-gray dot. The blue open contours surround the star sample with N and He abundance patterns not covered by the single-star evolutionary models considered.