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 have detected 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 resolve the apparent problem for stellar evolution, supporting the existing horizontal branch star canonical models, and may help to discern the nature of the GC polluters.
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The standard cosmological model states that massive galaxies contain a large fraction of dark matter. Dark matter is a transparent substance that does not interact through regular baryonic matter and is only detected through its gravitational pull over the stars and the gas. NGC 1277 is known as the prototype of a relic galaxy, that is, a galaxy that has not accreted other galaxies since it formed. Relic galaxies are extremely rare and are the untouched remains of the giant galaxies that populated the early Universe. Since relic galaxies are very important to understand the conditions in the
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It is well known that fullerenes – big, complex, and highly resistant carbon molecules with potential applications in nanotechnology – are mostly seen in planetary nebulae (PNe); old dying stars with progenitor masses similar to our Sun. Fullerenes, like C60 and C70, have been detected in PNe whose infrared (IR) spectra are dominated by broad unidentified IR (UIR) plateau emissions. The identification of the chemical species (structure and composition) responsible for such UIR emission widely present in the Universe is a mystery in astrochemistry; although they are believed to be carbon-rich
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CaII Kgrains, i.e., intermittent, short-lived (about 1 minute), periodic (2-4 minutes), pointlike chromospheric brightenings, are considered to be the manifestations of acoustic waves propagating upward from the solar surface and developing into shocks in the chromosphere. After the simulations of Carlsson and Stein, we know that hot shocked gas moving upward interacting with the downflowing chromospheric gas (falling down after having been displaced upward by a previous shock) nicely reproduces the spectral features of the CaII K profiles observed in such grains, i.e., a narrowband emission
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