A Model for Calculating the Abundances of Neutron-Capture Elements in Metal-Poor Stars

Several previous studies on the abundances of neutron-capture elements have indicated that, for most metal-poor stars, the observed abundances of the heavy elements cannot be matched by only one neutron-capture process, either the solar system r-process or the solar s-process abundances. However, the observed abundances can be well matched by the combined contributions from both of these solar system neutron-capture processes in certain proportions. So it is necessary to determine the relative contributions from the individual neutron-capture processes to the abundances of the heavy elements in metal-poor stars. In this paper we suggest a new concept of component coefficients to describe the relative contributions of the individual n-processes to the synthesis of the heavy elements and we set up a model to calculate the component coefficients and the abundances of heavy elements in metal-poor stars with different metallicities. With this model, we then calculate the component coefficients and the abundances of the heavy elements in 18 metal-poor stars. We find that, for most sample stars, the model calculations are basically in agreement with the observations of the heavy elemental abundances within the error limits and the fits of the model predictions are much better for the heaviest elements than for the lighter elements, specifically for Sr, Y, and Zr. We discuss this result and give a possible explanation for it. Moreover, we also discuss the physical meanings of the component coefficients.