On the Origin of the High Helium Sequence in $\omega$ Centauri

Abstract

The blue Main Sequence (bMS) of $\omega$ Cen implies a ratio of helium to metal enrichment $\Delta Y/\Delta Z\approx 70$, which is a major enigma. We show that rotating models of low metallicity stars, which account for the anomalous abundance ratios of extremely metal poor stars, are also useful for understanding the very high $\Delta Y/\Delta Z$ ratio in $\omega$ Cen. Models of massive stars with moderate initial rotation velocities produce stellar winds with large He-- and N--excesses, but without the large C-- (and O--) excesses made by very fast rotation, in agreement with the observed chemical abundance ratios in $\omega$ Cen. It is still uncertain whether the abundance peculiarities of $\omega$ Cen result from the fact that the high velocity contributions of supernovae escaped the globular cluster, usually considered as a tidally stripped core of a dwarf galaxy. Another possibility is a general dominance of wind ejecta at very low $Z$, due to the formation of black holes. Some abundance and isotopic ratios like $Mg/Al$, $Na/Mg$, $Ne/N$, ${}^{12}C{/}^{13}C$, ${}^{16}O{/}^{18}O$ and ${}^{17}O{/}^{18}O$ may allow us to further discriminate between these scenarios and between the AGB and massive star contributions.

5 pages, 3 figures, accepted for publication in A&A

Cited by in corpus (22)

• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• Scaled solar tracks and isochrones in a large region of the Z-Y plane I. From the ZAMS to the TP-AGB end for 0.15 - 2.5 Mo stars
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
• On the self-enrichment scenario of galactic globular clusters: Constraints on the IMF
• Origin of multiple stellar populations in globular clusters and their helium enrichment
• The fraction of second generation stars in Globular Clusters from the analysis of the Horizontal Branch
• A model for the Globular Cluster extreme anomalies
• Origin of Abundance Inhomogeneity in Globular Clusters
• Comparing CN and CH Line Strengths in a Homogeneous Spectroscopic Sample of 8 Galactic Globular Clusters
• Fe and Al Abundances for 180 Red Giants in the Globular Cluster Omega Centauri (NGC 5139)
• The self-enrichment scenario in intermediate metallicity globular clusters
• The chemical evolution of Omega Centauri's progenitor system
• Abundances on the Main Sequence of Omega Centauri
• Massive stars and globular cluster formation
• Observational consequences of the hypothesized helium rich stellar population in Omega Centauri
• Testing the AGB Scenario as the Origin of the Extreme-Helium Population in omega Centauri
• First stars as a possible origin for the helium-rich population in omega Centauri
• Surface pollution of main-sequence stars through encounters with AGB ejecta in omega Centauri
• Physics of rotation in stellar models
• Astrophysics in 2006
• Nucleosynthesis from massive stars 50 years after B2FH