The subgiant branch of omega Cen seen through high-resolution spectroscopy. I. The first stellar generation in omega Centauri?

Abstract

We analysed high-resolution UVES spectra of six stars belonging to the subgiant branch of omega Centauri, and derived abundance ratios of 19 chemical elements (namely Al, Ba, C, Ca, Co, Cr, Cu, Fe, La, Mg, Mn, N, Na, Ni, Sc, Si, Sr, Ti, and Y). A comparison with previous abundance determinations for red giants provided remarkable agreement and allowed us to identify the sub-populations to which our targets belong. We found that three targets belong to a low-metallicity population at [Fe/H]~-2.0 dex, [alpha/Fe]~+0.4 dex and [s/Fe]~0 dex. Stars with similar characteristics were found in small amounts by past surveys of red giants. We discuss the possibility that they belong to a separate sub-population that we name VMP (very metal-poor, at most 5% of the total cluster population), which - in the self-enrichment hypothesis - is the best-candidate first stellar generation in omega Cen. Two of the remaining targets belong to the dominant metal-poor population (MP) at [Fe/H]~-1.7 dex, and the last one to the metal-intermediate (MInt) one at [Fe/H]~-1.2 dex. The existence of the newly defined VMP population could help to understand some puzzling results based on low-resolution spectroscopy (Sollima et al., Villanova et al.) in their age differences determinations, because the metallicity resolution of these studies was probably not enough to detect the VMP population. The VMP could also correspond to some of the additional substructures of the subgiant-branch region found in the latest HST photometry (Bellini et al.). After trying to correlate chemical abundances with substructures in the subgiant branch of omega Cen, we found that the age difference between the VMP and MP populations should be small (0+/-2 Gyr), while the difference between the MP and MInt populations could be slightly larger (2+/-2~Gyr).

15 pages, 14 figures, accepted for publication by A&A

References in corpus (10)

• First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements
• Chemical Abundances for 855 Giants in the Globular Cluster Omega Centauri (NGC 5139)
• DAOSPEC: an automatic code for measuring equivalent widths in high-resolution stellar spectra
• The NIR Ca II triplet at low metallicity - Searching for extremely low-metallicity stars in classical dwarf galaxies
• Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397
• Origin of multiple stellar populations in globular clusters and their helium enrichment
• The Rotation of Sub-Populations in omega Centauri
• Fe and Al Abundances for 180 Red Giants in the Globular Cluster Omega Centauri (NGC 5139)
• Contrasting copper evolution in Omega Centauri and the Milky Way
• On the effect of helium enhancement on bolometric corrections and Teff-colour relations

Cited by in corpus (33)

• Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters
• The Pisa Stellar Evolution Data Base for low-mass stars
• Ceci n'est pas a globular cluster: the metallicity distribution of the stellar system Terzan 5
• Measuring helium abundance difference in giants of NGC 2808
• The metallicity spread and the age-metallicity relation of Omega Centauri
• The Terzan 5 puzzle: discovery of a third, metal-poor component
• A Spectroscopic Analysis of the Galactic Globular Cluster NGC 6273 (M19)
• Formation of Multiple Populations in Globular Clusters: Another Possible Scenario
• A chemical trompe-l'œil: no iron spread in the globular cluster M22
• Manganese in dwarf spheroidal galaxies
• Manganese Indicates a Transition from Sub- to Near-Chandrasekhar Type Ia Supernovae in Dwarf Galaxies
• The origin of the spurious iron spread in the globular cluster NGC 3201
• A critical look at the merger scenario to explain multiple populations and rotation in iron-complex globular clusters
• Mn abundances in the stars of the Galactic disc with metallicities -1.0 < [Fe/H] < 0.3
• Nucleosynthesis in helium-enriched asymptotic giant branch models: Implications for Heavy Element Enrichment in Omega Centauri
• Magnesium Isotope Ratios in omega Centauri Red Giants
• The helium abundance in the metal-poor globular clusters M30 and NGC6397
• Sodium abundances of AGB and RGB stars in galactic globular clusters I. Analysis and results of NGC 2808
• The Most Metal-poor Stars in Omega Centauri (NGC 5139)
• The chemical composition of NGC5824, a globular cluster without iron spread but with an extreme Mg-Al anticorrelation
• Blue straggler masses from pulsation properties. II. Topology of the Instability Strip
• The dynamics of the outer parts of omega Centauri
• Confirming the intrinsic abundance spread in the globular cluster NGC 6273 (M 19) with calcium triplet spectroscopy
• The subgiant branch of omega Cen seen through high-resolution spectroscopy. II. The most metal-rich population
• The peculiar properties of horizontal branch stars in omega Centauri
• A stellar census in globular clusters with MUSE. A new perspective on the multiple main sequences of $\omega$ Centauri
• Abundance ties: Nephele and the globular cluster population accreted with $\omega$ Cen. Based on APOGEE DR17 and Gaia EDR3
• Manganese evolution in Omega Centauri: a clue to the cluster formation mechanisms?
• Lithium abundance in lower red giant branch stars of Omega Centauri
• Variability in NGC 3201 giant stars and its impact on their spectroscopic [Fe/H] determination
• A new formation model for omega Centauri: the crossroad of astrophysical processes
• The Nephele ecosystem: stars, globular clusters, and stellar streams associated with the progenitor galaxy of $\omega$ Centauri
• Purveyors of fine halos III. Chemical abundance analysis of a potential omega Cen associate