oMEGACat. V. Helium Enrichment in omega Centauri as a Function of Metallicity

Constraining the helium enhancement in stars is critical for understanding the formation mechanisms of multiple populations in star clusters. However, measuring helium variations for many stars within a cluster remains observationally challenging. We use Hubble Space Telescope photometry combined with MUSE spectroscopic data for over 7200 red giant branch stars in ωCen to measure helium differences between distinct groups of stars as a function of metallicity, separating the impact of helium enhancements from other abundance variations on the pseudo-color (chromosome) diagram. Our results show that stars at all metallicities have subpopulations with significant helium enhancement (ΔYmin ≳ 0.11). We find a rapid increase in helium enhancement across low metallicities ([Fe/H] ≃ −2.05 to [Fe/H] ≃ −1.92), with this enhancement leveling out at ΔY = 0.15 at higher metallicities. The fraction of helium-enhanced stars steadily increases with metallicity from 10% at [Fe/H] ≃ −2.04 to over 90% at [Fe/H] ≃ −1.04. From these measurements, we calculate the total mass in helium produced over the cluster’s lifetime, finding M He tot ∼ 2.7 × 1 0 5 M ⊙ . This study is the first to examine helium enhancement across the full range of metallicities in ωCen, providing new insight into its formation history and additional constraints on enrichment mechanisms.