Influence of CN lines on the Zr–Na correlation. To account for the influence of CN blends, the original Zr abundances obtained from Zr I lines in Sect. 3.3.1 were modified by adding a correction which changed linearly from +0.04 dex at [Na/Fe] = 0.10 to −0.04 dex at [Na/Fe] = 0.75. A linear fit to the modified data (filled grey circles) is shown as a red solid line. The black dashed line is linear fit to the non-modified abundances in the [Zr/Fe] – [Na/Fe] plane shown in Fig. 5 (top panel) shifted to match the mean [Zr/Fe] value in the modified data at [Na/Fe] = 0.42.