Relation between nitrogen-to-carbon and nitrogen-to-oxygen ratios. Left panel: our results with (approximate) errors when including the uncertainties in T_eff and log g. Right panel: only those uncertainties that arise from our method when relying on the T_eff and log g values provided by Holgado et al. (2018; see Sect. 5.1). “Hot” and “cold” dwarfs are denoted by blue and red squares, and hot and cold supergiants/bright giants by cyan and magenta asterisks. For our division between hot and cold objects, and the correspondence between number and object, see Table 3. The solid lines represent the theoretical limits for the early phases of the CNO cycle (less massive stars), and for the conversion of O to N after afast establishment of CN equilibrium (most massive stars). Both curves adopt the initial abundances from the Geneva models (Ekström et al. 2012, see Sect. 6.1 and Table 4).