The puzzle of the CNO abundances of α Cygni variables resolved by the Ledoux criterion

  title={The puzzle of the CNO abundances of $\alpha$ Cygni variables resolved by the Ledoux criterion},
  author={Cyril Georgy and Hideyuki Saio and Georges Meynet},
  journal={Monthly Notices of the Royal Astronomical Society},
Recent stellar evolution computations show that the blue supergiant (BSG) stars could come from two distinct populations: a first group arising from massive stars that just left the main sequence (MS) and are crossing the Hertzsprung-Russell diagram (HRD) towards the red supergiant (RSG) branch, and a second group coming from stars that have lost considerable amount of mass during the RSG stage and are crossing the HRD for a second time towards the blue region. Due to very different luminosity… 

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