[C/N] ratio. Left panel: histogram for [C/N] of the stars in our K2 sample (gray, blue, and red histograms represent the low-α, old high-α, and young α-rich samples, respectively). Middle panel: [C/N] vs. mass for the stars in our sample, with colors as in the left panel. The solid lines represent the predictions of stellar evolution models from Vincenzo et al. (2021) at different metallicities ([Fe/H] = −1 in yellow, −0.5 in green, and +0.25 in purple). Right panel: [C/N] ratios for the entire sample color-coded by [Fe/H] (as indicated in the color scale). In this panel are shown low-α (dots), old high-α (triangles), and young-α rich stars (bigger dots).