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.