Spectral matching for abundances of 848 stars of the giant branches of the globular cluster ω Centauri

We present the effective temperatures, surface gravities and abundances of iron, carbon and barium of 848 giant branch stars, of which 557 also have well-defined nitrogen abundances, of the globular cluster omega Centauri. This work used photometric sources and lower resolution spectra for this abundance analysis. Spectral indices were used to estimate the oxygen abundance of the stars, leading to a determination of whether a particular star was oxygen rich or oxygen poor. The 557-star subset was analysed in the context of evolutionary groups, with four broad groups identified. These groups suggest that there were at least four main periods of star formation in the cluster. The exact order of these star formation events is not yet understood. These results compare well with those found at higher resolution and show the value of more extensive lower resolution spectral surveys. They also highlight the need for large samples of stars when working with a complex object like omega Cen.