Multiple populations are observed in many globular clusters including Omega Centauri.
There is now strong evidence that the multiple populations arise because of variations in
helium and other elements (C, N, O etc), with helium mass fraction as high as Y = 0.40
inferred for some clusters. However, the advanced evolutionary properties, chemical
yields, and final fates of He-rich stars are largely unexplored. We investigate the effect
of helium enrichment on the evolution and nucleosynthesis of low and intermediate-mass
asymptotic giant branch (AGB) stars at low metallicity (Z=0.0006 or [Fe/H] = -1.4) and at
higher metallicities (Z = 0.014 and 0.03, or [Fe/H] = 0 and +0.3). We find AGB models with
enhanced helium will evolve more than twice as fast, giving them the chance to contribute
sooner to the chemical evolution of the forming globular clusters and galaxies, and the
stellar yields will be strongly reduced relative to their primordial helium counterparts.
At low metallicity, we find that the minimum initial mass required for C burning and the
transition to super-AGB stars with CO(Ne) or ONe cores decreases from above our
highest-mass model (Mup > 6 Msun) for Y = 0.24 to 4-5Msun when Y = 0.40. This has
implications for the rates of neutron star production in clusters. At higher metallicities,
we find that helium enrichment can remove carbon stars from a population, which has
implications for finding carbon stars in the bulges of spiral galaxies such as our own and
M31.
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