case western reserve university



THE MOST METAL-POOR STARS -- -5.5 < [Fe/H] < -3.5

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

The discovery and analysis of metal-poor stars lead to insight into conditions when the Universe and Galaxy were young. We present the rationale for studying such objects (which become progressively rarer at lowest abundance), with a description of their systematic discovery, culminating in the recent analysis of two objects having [Fe/H] < -5.0, and a third which appears to have [Fe/H] ~ -4.5. We discuss the Metallicity Distribution Function and the abundance patterns of several elements. As one proceeds to lowest abundance one finds astounding overabundances of some or all of the CNO group and the lighter alpha elements. While this diversity among the most metal-poor stars has yet to be fully understood, there exists a rapidly-increasing number of suggested models, which will be briefly addressed.