![Colour-magnitude diagram (a form of the Hertzsprung-Russell diagram) of the globular cluster M13. The AGB stars of the first and second generations are shown in blue and red, respectively, while the less evolved red giants are shown in green. Crédits: ada Colour-magnitude diagram (a form of the Hertzsprung-Russell diagram) of the globular cluster M13. The AGB stars of the first and second generations are shown in blue and red, respectively, while the less evolved red giants are shown in green. Crédits: ada](/sites/default/files/styles/crop_square_2_2_to_320px/public/images/news/resultados160_177.jpg?itok=RojKIX2M)
Galactic globular clusters (GCs) are known to host multiple stellar populations: a first generation (FG) with a chemical pattern typical of halo field stars and a second generation (SG) enriched in Na and Al and depleted in O and Mg. Both stellar generations are found at different evolutionary stages (e.g., the main-sequence turnoff, the subgiant branch, and the red giant branch (RGB)). The non-detection of SG asymptotic giant branch (AGB) stars in several metal-poor ([Fe/H] < ‑1) GCs suggests that not all SG stars ascend the AGB phase, and that failed AGB stars may be very common in metal
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