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New Metallicities of RR Lyrae Stars in omega Centauri: Evidence for a Non He-Enhanced Metal-Intermediate Population

A. Sollima·J. Borissova·M. Catelan·H. A. Smith·D. Minniti·C. Cacciari·F. R. Ferraro
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Abstract

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.

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A. Sollima, J. Borissova, M. Catelan, H. A. Smith, D. Minniti, C. Cacciari, F. R. Ferraro. 2006-02-02. New Metallicities of RR Lyrae Stars in omega Centauri: Evidence for a Non He-Enhanced Metal-Intermediate Population. https://doi.org/10.1086/503099

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