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 ] } \sim - 1.2 ) are fainter than the bulk of the dominant metal-poor population ( { [ Fe / H ] } \sim - 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 ] } \sim - 1.2 ) and different helium abundances has to be considered .