Abundance Analysis Of R+Stars: R-process Abundance Comparison Between R+s Stars And R-rich Stars

The elemental abundances of s+r stars provide important clues to s-and r-processnucleosynthesis in the early Galaxy. Using parametric model we fit the elemental abundancesof32s+r stars. We find that s-process abundance pattern, main r-process abundance patternand weak r-process abundance pattern adopted in this work are remarkably stable from star tostar. Because the elemental abundance are disposed by neutron capture nucleosynthesis, wecan derive the relative fraction to s-, main r-and weak r-process in every element.There are three important results in this paper as follows:1. The origins of weak r-process material in s+r stars and r-rich stars are similar: they areboth formed in the molecular cloud which had been polluted by weak r-process material.2. The yields of main r-process in r-rich stars have primary nature but those of r-processrelated to r+s stars have secondary nature. This unexpected result implies that, firstly, thephysics condition of the r-process related to r+s stars is different from the normal r-process, atleast partly; secondly, the progenitor mass or nucleosynthesis site of this r-process would bedifferent from the normal r-process.3. Although the origin and the site of r-process are quite different from those of thes-process, there is a strong correlation between the enhancement of r-process and s-process inr+s stars. The r-process matter accreted from the origin of r-process, such as AIC or SN1.5,has an increasing trend with increasing s-process matter accreted from the AGB star.Overall, the number of r+s stars is still small, making proposed enrichment scenariosdifficult to explicitly test. Our hope is that the results here will provide a useful understand forthe chemical evolution in the early Galaxy and the formation scenarios in s+r stars.