Study Contribution of Neutron-capture Elements Abundance R-process in Metal-poor Stars
|Keywords||metal-poor star neutron capture element nucleosynthesis r-process s-process|
Metal-poor stars called a "fossil" provide records of the Galaxy chemical evolution history.It is great significant to study nucleosynthesis theories and explore the early galaxy formation. In recent years, discovery of s-process nucleosynthesis theory of AGB stars has already made more progress than that of r-process. At present,researching the astrophysical site and physical conditions about r-process nucleosynthesis of metal-poor stars is still important topics. But the research to the environment synthesizes of r-process is just start theoretically. The contribution of synthesizes process to the neutron capture element abundances of the poor metals star it is still not determined with certainty.This study consists of two parts.In chapter 2, a parametric model of r-rich metal-poor stars is made to calculate the abundances of neutron capture element. Furthermore, we can predict the element abundance of the r-rich metal-poor stars from the parametric model and explore the rules and characteristic of abundance pattern. As the astrophysical site of the r-process is not known, we explore the possibility site of a neutron capture r-process .Based on Galaxy chemical evolution and nucleosynthesis theories , this paper put forward that the mixing pattern of the week r-process (light element primary process-LEPP) and the main r-process in a large sample r-rich metal-poor stars maybe explain such apparent r-process heavy elemental abundances pattern.Because typical stars can show the characteristic of nucleosynthesis ,We suggest HD 122563 and CS 22892-001 as typical stars to describe pure week r-process and pure main r-process star abundances pattern of heavy elements in metal-poor stars, respectively. We regard abundances of Eu as a pure main r-process yield in metal-poor stars and calculated component coefficient of the 78 sample stars according to our parametric model that is based on observational constraints as here,then predicted abundances of heavy neutron capture elements in the r-rich metal-poor stars.The result shows:(1) The abundances of heavy neutron capture elements can be well explained as resulting from a combination both components of the weak and main r-process nucleosynthesis contributions in the r-rich metal-poor stars.(2) It shoud be thought about the combined contributions from three components of the weak r-process and main r-process and week s-process in the week r-metal-poor stars.In chapter 3, bacause the heavy-element abundances in Solar-system are sums contributions of the three neutron capture processes, knowing the week s-process and main s-process determination of the r-process contributions, we adopt the standard of Solar-system nucleosynthesis elements abundance distributions and set up our modle to contrast metal-poor stars with solar-system heavy element abundances. Furthermore,we regard abundances of Sr、Ba、Eu as typical element abundances to describe s-week,s-main,r-process yield in metal-poor, respectively. Based on observational constraints,we reseached contributions of different nucleosynthesis to abundances of heavy neutron capture elements in the different metallicity metal-poor stars.The proportion of contributions to abundance of heavy elements from three components in stars is closer to the Solar-System when metallicity of star is higher (-1<[Fe/H]<0). While also detected abundances of heavy neutron capture element, with respect to the solar-system r-process pattern,because the production of such heavy elements by the s-process is very small in the lower metallicity ([Fe/H]<-1). The result shows,the lower metallicity,the smaller the contribution of s-week、s-main is and the bigger of r-process is, s-week is almost no contribution early galaxies.In this paper, these parametrics associate with the chemical evolution, hence our work is great significance.