EVENT: Galactic Archaeology and the New HERMES spectrometer on the Anglo Australian Telescope

Our Galaxy has been forming stars continuously since just after the Big Bang. Its stars form in fairly large groups but they do not stay together. The groups of stars soon dissolve and their stellar debris is spread right around the Galaxy.

The goal of Galactic archaeology is to use the fossil remnants of these past star formation events to probe the history of our Galaxy.

The problem is to identify the fossil remnants. How do we find stars that were born together but have since drifted apart ? We use chemical techniques: stars that formed together have very similar element abundances over a wide range of chemical elements. There are at least 7 groups of elements which vary independently from star to star. We can think of the stars populating a 7-dimensional 'chemical space' of element abundances: the debris of an individual star-forming event lies in a clump in this chemical space.

The approach is called chemical tagging. To make it work, we need to measure abundances of many chemical elements in about a million stars. Until now, this has been impossible. The new HERMES instrument for the AAT is the first of a new generation of high resolution multi-object spectrometers built for this purpose. We hope to start observations in 2012. The survey should take about four years.