case western reserve university



Extremely Metal-Poor Stars

John E.Norris (Mount Stromlo & Siding Spring Observatories, The Australian National University)

The discovery and analysis of extremely metal-poor stars have led to increasing insight into conditions when the Universe and Galaxy were young. We present the rationale for studying such objects, with a description of their systematic discovery, culminating in the recent analysis of an object having [Fe/H] = -5.3. We discuss the abundance patterns of several elements from Li through to the heavy-neutron-capture elements. Relatively few extremely metal-poor stars with [Fe/H] < -3.5 have been analyzed at high spectral resolution and high signal-to-noise, but some 30% of that sample show astounding overabundances of some or all of the CNO group and the lighter alpha-elements. At [Fe/H] ~-3.0, some stars show enormous enhancements of r-process elements, leading to age determinations. The diversity among the most metal-poor stars has yet to be fully understood.