1996A&A...305..911B

Carbon, nitrogen and oxygen abundances were measured in a sample of 9 yellow supergiants for which accurate rotational velocities are now available. We obtain [O/Fe]≃-0.2, a result consistent with other young objects (main sequence B stars, planetary nebulae, H II regions). We also find [C/Fe]≃-0.2 for 7 stars, and ≃0.0 for another 2 ones, and [N/Fe]≃0.0 for 6 stars and ≃+0.2 for the other 3 ones. Stars showing low carbon and/or high nitrogen are assumed to show convective mixing effects. The present results seem to indicate that, among the low rotation supergiants located near the rotational discontinuity at F9Ib, a fraction of them shows no mixing, and another fraction does show mixing effects, probably depending on their evolutionary stage.