r-Process Abundance Signatures in Metal-Poor Halo Stars
  Abundance observations indicate the presence of rapid-neutron capture (i.e.,
r-process) elements in old Galactic halo and globular cluster stars. Recent
observations of the r-process-enriched star BD +17 3248 include new abundance
determinations for the neutron-capture elements Cd I (Z=48), Lu II (Z = 71) and
Os II (Z = 76), the first detections of these elements in metal-poor
r-process-enriched halo stars. Combining these and previous observations, we
have now detected 32 n-capture elements in BD +17 3248. This is the most of any
metal-poor halo star to date. For the most r-process-rich (i.e. [Eu/Fe] ~= 1)
halo stars, such as CS 22892-052 and BD +17 3248, abundance comparisons show
that the heaviest stable n-capture elements (i.e., Ba and above, Z >= 56) are
consistent with a scaled solar system r-process abundance distribution. The
lighter n-capture element abundances in these stars, however, do not conform to
the solar pattern. These comparisons, as well as recent observations of heavy
elements in metal-poor globular clusters, suggest the possibility of multiple
synthesis mechanisms for the n-capture elements. The heavy element abundance
patterns in most metal-poor halo stars do not resemble that of CS 22892-052,
but the presence of heavy elements such as Ba in nearly all metal-poor stars
without s-process enrichment indicates that r-process enrichment in the early
Galaxy is common.
