Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-02-02
Astrophys.J. 640 (2006) L43-L46
Astronomy and Astrophysics
Astrophysics
9 pages, 4 figures, accepted for publication by ApJL
Scientific paper
10.1086/503099
We present new spectroscopic metal abundances for 74 RR Lyrae stars in omega Cen obtained with FLAMES. The well-known metallicity spread is visible among the RR Lyrae variables. The metal-intermediate (MInt) RR Lyrae stars ([Fe/H] ~ -1.2) are fainter than the bulk of the dominant metal-poor population ([Fe/H] ~ -1.7), in good agreement with the corresponding zero-age horizontal branch models with cosmological helium abundance Y = 0.246. This result conflicts with the hypothesis that the progenitors of the MInt RR Lyrae stars correspond to the anomalous blue main-sequence stars, which share a similar metallicity but whose properties are currently explained by assuming for them a large helium enhancement. Therefore, in this scenario, the coexistence within the cluster of two different populations with similar metallicities ([Fe/H] ~ -1.2) and different helium abundances has to be considered.
Borissova Jordanka
Cacciari Carla
Catelan Márcio
Ferraro Francesco R.
Smith Harold A.
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