New Metallicities of RR Lyrae Stars in ω Centauri: Evidence for a Non-He-enhanced Metal-intermediate Population

Abstract

We present new spectroscopic metal abundances for 74 RR Lyrae (RRL) stars in q Cen obtained with FLAMES. The well-known metallicity spread is visible among the RRL variables. The metal-intermediate (MI) RRL 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 modelswith cosmological helium abundanceYp0.246. This result conflicts with the hypothesis that the progenitors of theMI 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] ∼ -1.2) and different helium abundances has to be considered.