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A small set of chemically old stars that appear young by their independentlyderived masses has been detected. These are so-called $\alpha$-rich youngstars. For a sample of 51 red-giant stars, for which spectra are available fromSDSS/APOGEE and masses are available from asteroseismic measures based on\textit{Kepler} lightcurves, we derive the C, N and O abundances through anindependent analysis. These stars span a wide range of N/C surface numberdensity ratios. We interpret the high-mass stars with low N/C as being productsof mergers or mass transfer during or after first dredge up, because thedredge-up features are the same as for low-mass stars. The $\alpha$-rich youngstars with high N/C follow the expected trend of N/C for their mass, and couldbe either genuine young stars (leaving their high [$\alpha$/Fe] unexplained) orthe results of mergers on the main sequence.

Origin of $\alpha$-rich young stars: clues from C, N and O