The first stars: a classification of CEMP-no stars

Aims. We propose and apply a new classification for the CEMP no stars, which are carbon-enhanced metal-poor stars with no overabundance of s-elements and with [Fe/H] generally <=-2.5. Methods. This classification is based on the changes in abundances for the elements and isotopes involved in the CNO, Ne-Na, and Mg-Al nuclear cycles. These abundances change very much owing to successive back and forth mixing motions between the He- and H-burning regions in massive stars (the source stars responsible for the chemical enrichment of the CEMP no stars). Results. The wide variety of the ratios [C/Fe], C-12/C-13, C, [N/Fe], [0/Fe], [Na/Fe], [Mg/Fe], [Al/Fe], [Sr/Fe], and [Ba/Fe], which are the main characteristics making the CEMP no and low-s stars so peculiar, is described well in terms of the proposed nucleosynthetic classification. We note that the [(C+N+O)/Fe] ratios significantly increase for lower values of [Fe/H]. Conclusions. The classification of CEMP-no stars and the behavior of [(C+N+O)/Fe] support the presence, in the first stellar generations of the Galaxy, of fast-rotating massive stars experiencing strong mixing and mass loss (spinstars). This result has an impact on the early chemical and spectral evolution of the Galaxy.