Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2010-12-21
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
ApJ in press. 29 pages, 11 figures
Scientific paper
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.
Dupree Andrea K.
Smith Graeme H.
Strader Jay
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