García-Hernández, D. A.; Mészáros, Sz.; Monelli, M.; Cassisi, S.; Stetson, P. B.; Zamora, O.; Shetrone, M.; Lucatello, S.
Bibliographical reference
The Astrophysical Journal Letters, Volume 815, Issue 1, article id. L4, 7 pp. (2015).
Description
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-poor GCs. This
observation represents a serious problem for stellar evolution and GC
formation/evolution theories. We report fourteen SG-AGB stars in four
metal-poor GCs (M13, M5, M3, and M2) with different observational
properties: horizontal branch (HB) morphology, metallicity, and age. By
combining the H-band Al abundances obtained by the Apache Point
Observatory Galactic Evolution Experiment survey with ground-based
optical photometry, we identify SG Al-rich AGB stars in these four GCs
and show that Al-rich RGB/AGB GC stars should be Na-rich. Our
observations provide strong support for present, standard stellar
models, i.e., without including a strong mass-loss efficiency, for
low-mass HB stars. In fact, current empirical evidence is in agreement
with the predicted distribution of FG and and SG stars during the
He-burning stages based on these standard stellar models.
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Galaxy Evolution in the Local Group
Galaxy formation and evolution is a fundamental Astrophysical problem. Its study requires “travelling back in time”, for which there are two complementary approaches. One is to analyse galaxy properties as a function of red-shift. Our team focuses on the other approach, called “Galactic Archaeology”. It is based on the determination of galaxy
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Low- to intermediate-mass (M < 8 solar masses, Ms) stars represent the majority of stars in the Cosmos. They finish their lives on the Asymptotic Giant Branch (AGB) - just before they form planetary nebulae (PNe) - where they experience complex nucleosynthetic and molecular processes. AGB stars are important contributors to the enrichment of the
Domingo Aníbal
García Hernández