Multiple stellar populations in Asymptotic Giant Branch stars of Galactic Globular Clusters

Abstract

Multiple stellar populations (MPs) are a distinct characteristic of Globular Clusters (GCs). Their general properties have been widely studied among main sequence, red giant branch (RGB) and horizontal branch (HB) stars, but a common framework is still missing at later evolutionary stages. We studied the MP phenomenon along the AGB sequences in 58 GCs, observed with the Hubble Space Telescope in ultraviolet (UV) and optical filters. By using UV-optical color-magnitude diagrams, we selected the AGB members of each cluster and identified the AGB candidates of the metal-enhanced population in type II GCs. We studied the photometric properties of AGB stars and compared them to theoretical models derived from synthetic spectra analysis. We observe the following features: i) the spread of AGB stars in photometric indices sensitive to variations of light-elements and helium is typically larger than that expected from photometric errors; ii) the fraction of metal-enhanced stars in the AGB is lower than in the RGB in most of the type II GCs; iii) the fraction of 1G stars derived from the chromosome map of AGB stars in 15 GCs is larger than that of RGB stars; v) the AGB/HB frequency correlates with the average mass of the most helium-enriched population. These findings represent a clear evidence of the presence of MPs along the AGB of Galactic GCs and indicate that a significant fraction of helium-enriched stars, which have lower mass in the HB, does not evolve to the AGB phase, leaving the HB sequence towards higher effective temperatures, as predicted by the AGB-manqué scenario.

32 pages, 19 figures, 3 tables

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• Spectroscopy and photometry of the least-massive Type-II globular clusters: NGC1261 AND NGC6934
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• Chromosome maps of Globular Clusters from wide-field ground-based photometry
• Multiple Stellar Populations in Metal-Poor Globular Clusters with JWST: a NIRCam view of M92
• Testing for Dark Matter in the Outskirts of Globular Clusters
• HST observations of the globular cluster NGC 6402 (M14) and its peculiar multiple populations
• Integrated photometry of multiple stellar populations in Globular Clusters
• Euclid preparation. LVIII. Detecting globular clusters in the Euclid survey
• Isochrone fitting of Galactic globular clusters -- V. NGC6397 and NGC6809 (M55)
• Exploring the formation environment of multiple stellar populations in Globular Clusters through binary systems
• The chemical compositions of multiple stellar populations in the globular cluster NGC 2808
• AstroSat study of the globular cluster NGC 2298: probable evolutionary scenarios of hot HB stars
• The Origin of Young Stellar Populations in NGC 1783: Accretion of External Stars
• Light Element Abundances and Multiple Populations in M53