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Australian Human Resources Institute Diversity Awards 2013 Finalist

Jeffrey Simpson (University of Canterbury)

"Spectral matching for elemental abundances of evolved stars of omega Centauri"

Abstract. In order to understand the origin of globular clusters, large samples of their stars need to be observed and analyzed for their chemical composition. This is especially true for the complex, multimetallic cluster omega Centauri with its large range of iron, carbon, nitrogen, oxygen, sodium and barium abundances. In order to accomplish this, an automated spectral matching pipeline was developed to determine these abundances for hundreds of stars. My research makes use of photometry and low resolution spectroscopy to analyze the chemical composition of evolved stars in three clusters: omega Centauri, 47 Tuc and NGC 6752. The latter two clusters are monometallic and selected due their similar metallicities to the metal-rich and metal-poor stars in omega Centauri. This allowed them to be used as test-cases for the spectral matching pipeline.

Subsequent to the abundance analysis, k-means clustering analysis was used to group the stars in omega Centauri into four groups based upon these abundances. 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, with some models predicting the groups formed from iron-poorest to iron-richest, while others suggest the potential for iron-poorer groups to form after iron-rich groups.

These results compare well with those found from higher resolution studies 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 Centauri.

Held in the AAO Meeting Room (Room 7, 1st Floor, Building 2) at 11:00 AM on Thursday, 04 July 2013