oMEGACat V: Helium Enrichment in $\omega$ Centauri as a Function of Metallicity

TL;DR

This study uses Hubble and MUSE data to measure helium variations in over 7,200 stars in extomega Centauri, revealing how helium enrichment correlates with metallicity and informing cluster formation theories.

Contribution

It provides the first comprehensive analysis of helium enhancement across all metallicities in extomega Centauri, offering new insights into its formation and enrichment processes.

Findings

Helium enhancement is significant at all metallicities.

Helium enhancement increases rapidly with metallicity at low values.

The fraction of helium-enhanced stars rises from 10% to over 90% with increasing metallicity.

Abstract

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 7,200 red-giant branch stars in \omc\ 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) diagrams. Our results show that stars at all metallicities have subpopulations with significant helium enhancement ($\Delta Y_{min} \gtrsim$ 0.11). We find a rapid increase in helium enhancement from low metallicities ($\rm{[Fe/H] \simeq -2.05}$ to $\rm{[Fe/H] \simeq -1.92})$, with this enhancement leveling out at \deltay\ $= 0.154$ at higher metallicities. The fraction of helium-enhanced stars steadily increases with metallicity ranging from 10\% at $\rm{[Fe/H] \simeq -2.04}$ to over $90\%$ at $\rm{[Fe/H] \simeq -1.04}$. This study is the first to examine helium enhancement across the full range of metallicities in \omc{}, providing new insight into its formation history and additional constraints on enrichment mechanisms.