Browsing by Author "Cacciari, C"

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    New metallicities of RR Lyrae stars in ω Centauri
    (2006) Sollima, A; Borissova, J; Catelan, M; Smith, HA; Minniti, D; Cacciari, C; Ferraro, FR
    We present new spectroscopic metal abundances for 74 RR Lyrae (RRL) stars in omega Cen obtained with FLAMES. The well-known metallicity spread is visible among the RRL variables. The metal-intermediate (MI) RRL stars ([Fe/H] similar to -1.7) are fainter than the bulk of the dominant metal-poor population ([Fe/H] similar to -1.7), in good agreement with the corresponding zero-age horizontal-branch models with cosmological helium abundance. This result Y = 0.246 conflicts with the hypothesis that the progenitors of the MI RRL 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] similar to -1.7) and different helium abundances has to be considered.