We present abundances of several light , \alpha , Fe–peak , and neutron–capture elements for 66 red giant branch ( RGB ) stars in the Galactic globular cluster Omega Centauri ( \omega Cen ) .
Our observations lie in the range 12.0 < V < 13.5 and focus on the intermediate and metal–rich RGBs .
Abundances were determined using equivalent width measurements and spectrum synthesis analyses of moderate resolution ( R \approx 18,000 ) spectra obtained with the Blanco 4m telescope and Hydra multifiber spectrograph .
Combining these data with previous work , we find that there are at least four peaks in the metallicity distribution function at [ Fe/H ] =–1.75 , –1.45 , –1.05 , and –0.75 , which correspond to about 55 \% , 30 \% , 10 \% , and 5 \% of our sample , respectively .
Additionally , the most metal–rich stars are the most centrally located .
Na and Al are correlated despite exhibiting star–to–star dispersions of more than a factor of 10 , but the distribution of those elements appears to be metallicity dependent and are divided at [ Fe/H ] \approx –1.2 .
About 40–50 \% of stars with [ Fe/H ] < –1.2 have Na and Al abundances consistent with production solely in Type II supernovae and match observations of disk and halo stars at comparable metallicity .
The remaining metal–poor stars are enhanced in Na and Al compared to their disk and halo counterparts and are mostly consistent with predicted yields from > 5 M _ { \sun } asymptotic giant branch ( AGB ) stars .
At [ Fe/H ] > –1.2 , more than 75 \% of the stars are Na/Al enhanced and may have formed almost exclusively from AGB ejecta .
Most of these stars are enhanced in Na by at least 0.2 dex for a given Al abundance than would be expected based on “ normal ” globular cluster values .
All stars in our sample are \alpha –rich with \langle [ Ca/Fe ] \rangle =+0.36 ( \sigma =0.09 ) and \langle [ Ti/Fe ] \rangle =+0.23 ( \sigma =0.14 ) .
The Fe–peak elements give solar–scaled abundances and similarly small dispersions with \langle [ Sc/Fe ] \rangle =+0.09 ( \sigma =0.15 ) and \langle [ Ni/Fe ] \rangle =–0.04 ( \sigma =0.09 ) .
Europium does not vary extensively as a function of metallicity and has \langle [ Eu/Fe ] \rangle =+0.19 ( \sigma =0.23 ) .
However , [ La/Fe ] varies from about –0.4 to +2 and stars with [ Fe/H ] \gtrsim –1.5 have [ La/Eu ] values indicating domination by the s–process .
A quarter of our sample have [ La/Eu ] \geq +1 and may be the result of mass transfer in a binary system .
We conclude that the metal–rich population must be at least 1–2 Gyr younger than the metal–poor stars , owing to the long timescales needed for strong s–process enrichment and the development of a large contingent of mass transfer binaries .