We present a chemical-composition analysis of 77 red-giant stars in Omega Centauri .
We have measured abundances for carbon and nitrogen , and combined our results with abundances of O , Na , La , and Fe that we determined in our previous work .
Our aim is to better understand the peculiar chemical-enrichment history of this cluster , by studying how the total C+N+O content varies among the different-metallicity stellar groups , and among stars at different places along the Na-O anticorrelation .
We find the ( anti ) correlations among the light elements that would be expected on theoretical ground for matter that has been nuclearly processed via high-temperature proton captures .
The overall [ ( C+N+O ) /Fe ] increases by \sim 0.5 dex from [ Fe/H ] \sim - 2.0 to [ Fe/H ] \sim - 0.9 .
Our results provide insight into the chemical-enrichment history of the cluster , and the measured CNO variations provide important corrections for estimating the relative ages of the different stellar populations .