  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.

Astrophysics