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 10830Å 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 ] \geq - 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 .