We present spectroscopic abundances and radial velocities for giant stars in the Galactic globular cluster \omega Centauri based on the \ion Ca2 infrared triplet .
Two samples of stars were observed : 234 stars at M _ { V } \sim 1.25 on the lower giant branch at radial distances between 8 \arcmin and 23 \arcmin , and 145 stars at M _ { V } \sim - 1.3 at radial distances between 3 \arcmin and 22 \arcmin .
We found 199 and 144 radial velocity members , respectively , in the two samples .
These samples were corrected for evolutionary effects to provide an unbiased distribution of the underlying stellar metallicity .
We find < v _ { r } > = 234.7 \pm 1.3 , \sigma _ { obs } = 11.3 km s ^ { -1 } ( bright sample ) , and < v _ { r } > = 232.9 \pm 1.2 , \sigma _ { obs } = 10.6 km s ^ { -1 } ( faint sample ) .
The statistical errors of the dispersions are less than 1 km s ^ { -1 } .

Previous metallicity studies found a non-gaussian metallicity distribution containing a tail of metal-rich stars .
We confirm these results except our unbiased cluster metallicity distributions are narrower .
They contain the following key features : ( 1 ) No very metal-poor stars ( 2 ) a sudden rise in the metal-poor distribution to a modal [ Fe/H ] value of –1.70 consistent with an homogeneous metallicity unresolved at the 0.07 dex level , ( 3 ) a tail to higher metallicities with more stars than predicted by simple chemical evolution models , and ( 4 ) a weak correlation between metallicity and radius such that the most metal-rich stars are concentrated to the cluster core .
The unresolved metal-weak tail implies that the gas out of which \omega Cen formed was well-mixed up to the modal metallicity of the cluster .
Therefore , \omega Cen like other Galactic globular clusters , seems to have formed in a pre-enriched and homogenized ( up to the modal metallicity ) environment .

The existence of a weak metallicity gradient supports the idea that \omega Cen self-enriched , with the enriched gas sinking to the cluster center due to gas dissipation processes .
We also note , however , that the metal-rich stars are more massive than the bulk of the stars in the cluster , and could also have sunk to the center by dynamical mass segregation over the lifetime of the cluster .