Direct Evidence for an Enhancement of Helium in Giant Stars in Omega Centauri

TL;DR

This study provides the first direct evidence of helium enhancement in Omega Centauri's giant stars, showing a correlation with certain element abundances, which supports theories of high-temperature stellar processing.

Contribution

It presents direct spectroscopic evidence of helium variation in Omega Centauri, linking helium enrichment to specific elemental abundances and stellar evolutionary processes.

Findings

Helium is detected in stars with [Fe/H] >= -1.8.

Helium presence correlates with increased [Al/Fe] and [Na/Fe].

No helium detection in the most metal-poor stars.

Abstract

The double main sequence identified in the globular cluster Omega Centauri has been interpreted using isochrones to indicate a large variation in the abundance of helium. If true, a helium enhancement carries strong implications for the chemical and stellar evolutionary history of this cluster. However, only indirect measures currently support this conjecture. We report the discovery of a variation in the line strength of the near-infrared He I 10830 A transition in twelve similar red giants in Omega Centauri observed with PHOENIX on Gemini-S. Abundances of these stars derived from Magellan/MIKE spectra taken at Las Campanas Observatory show that the helium transition is not detected in the most metal-poor population ([Fe/H] < -1.8), yet is present in the majority of stars with [Fe/H] >= -1.8. These observations give the first direct evidence for an enhancement of helium in Omega Centauri. The appearance of helium appears better correlated with increased [Al/Fe] and [Na/Fe] abundances than as a function of [Fe/H], giving observational support to the presence of high-temperature H-burning in a prior generation of stars.