Study of Neutron-Capture Element Abundances in Metal-Poor Stars
  This work describes a study of elemental abundances for 30 metal-poor stars
whose chemical abundances provide excellent information for setting constraints
on models of neutron-capture processes. Based on the abundances of main r- and
weak r-process stars, the abundance patterns of main r-process and weak
r-process are obtained. The two r-process component coefficients are defined to
determine the relative contributions from individual neutron-capture process to
abundances of metal-poor stars. Based on the component coefficients, we find
that metal-poor stars BD+4 2621 and HD 4306 are also weak r-process stars,
which means that the abundance pattern produced by weak r-process is stable.
All metal-poor star abundances contain the contributions of both main r-process
and weak r-process. The elements produced by weak r-process have increased
along with Fe over the polluted history. Most of the metal-poor star abundances
do not follow the pattern observed in solar system, but there is a small
fraction that do. For the low-[Sr/Fe] star BD-18 5550 ([Sr/Fe]$\lesssim-1$),
neutron-capture element abundances can be explained by the mixture of two
r-process components. Since lighter elements in this star cannot be fitted by
the two components, the abundance pattern of P-component is estimated from
those abundances.
