The chemical abundances of the metal-poor star are an excellent test bed to set new constraints on models of neutron-capture processes at low metallicity .
Some r-rich metal-poor stars , such as HD 221170 , show overabundance of the heavier neutron-capture elements and excesses of lighter neutron-capture elements .
The study for these r-rich stars could make us get a better understanding of weak r- and main r-process nucleosynthesis at low metallicity .
Based on the conclusions of the observation of metal-poor stars and neutron-capture element nucleosynthesis theory , we set up a model to determine the relative contributions from weak r- and main r-process to the heavy element abundances in metal-poor stars .
Using this model , we find that the abundance patterns of light elements for most sample stars are close to the pattern of the weak r-process star , and heavier neutron-capture elements is very similar to main r-process star , while the lighter neutron-capture elements can be fitted by mixing of weak r- and main r-process material .
The production of the weak r-process elements appears to be associated with the light elements and the production of main r-process elements are almost decoupled from that of the light elements .
We compare our results with the observed data at low metallicities , showing that the predicted trends are in good agreement with the observed trends , at least for the metallicity range [ Fe/H ] < -2.1 .
For most of sample stars , the abundance pattern of both neutron-capture elements and light elements could be best explained by a star formed in a molecular cloud that had been polluted by both weak r- and main r-process material .