SIMBAD references

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 Å transition in 12 similar red giants in Omega Centauri observed with PHOENIX on Gemini-S. Abundances of these stars derived from Magellan/MIKE spectra taken at the 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.