Study Of The Quantitative Decomposition Of Stellar Neutron-capture Element Abundances

The elemental abundances provide some important information about the formation andevolution of the stars and galaxies for us. It is the important content of nuclear astrophysics tostudy the origin of the elemental abundances. The astrophysical origins of elements arevarious and the processes of production are very complex. This indicates that the observedabundances of stars usually can not be explained by a single process. In this case, wedecompose the stellar abundances and discuss the results.The elemental abundances of metal-poor stars, especially their neutron-capture elementabundances, provide important clues to study the evolution of the stars during the earlyGalaxy for us. In this paper, based on the abundances of main r-process CS22892-052, CS31082-001and weak r-process stars HD122563, HD88609, we derived the abundancepatterns of main r-process and weak r-process. The observed abundances of metal-poor starsshow that the light elements and iron-group elements should be coupled with the weakr-process elements, so the weak r-process pattern is derived to the light elements andiron-group elements. Using main r-process component and weak r-process component, wedecompose the observed abundances of30metal-poor stars. We find two of them are weakr-process stars by analyzing the component coefficients. The results suggest the observedabundances of “low-[Sr/Fe] stars” BD-185550can not be fitted, because the contribution of Pcomponent from the massive stars in the early Galaxy is not contained. For light elements andiron group elements, the calculated results are larger than their observed abundances, thismeans that the P component contribution the star should not be ignored. We obtain theabundance pattern of P component through substracting the calculated values from observedabundances. Using main r-process component, weak r-process component and P component,we refit the abundances of these stars. We find the contributions of P component decreaserapidly with the increasing metallicities.The study of metal-poor stellar stream suggests that the weak r-process coefficients ofstream stars are almost constant. This means that the abundances of the weak r-processelements have increase along with those of element Fe over the polluted history of the stellarstream and that the weak r-process elements and Fe are produced by SNe II in a nearly constant mass fraction. We find there is a weak r-process star HD237846in the stellar stream.Its metallicity ([Fe/H]=3.29) is even lower than that of HD88609. This implies that theweak r-process pattern is very stable in a wider metallicity range. At the [Fe/H]＞-2.2,Cr,mis close toCr,w, which means that the ratio between the contributions of weak r-process andmain r-process to the stream stars are close to the ratio of solar system. CS29513-032is as-rich steam star whose s-procss elements are a result of pollution from the low-mass AGBstar. We find that its r-process coefficients are close to other stream stars with similarmetallicity, which implies that the astrophysical origin of CS29513-032and other streamstars is similar.Based on the comparision between observed abundances of CS22892-052, CS31082-001and HD122563，HD88609, we estimate progenitor mass and yields of weakr-process and main r-process. We find that the weak r-process occurs in the supernova withthe progenitor mass range of～11-26M⊙and that the SNe with progenitor mass range about15M⊙<M <26M⊙are the main sites of weak r-process, which contributed the integratedratio larger than80%.The abundances of M22stars can be decomposed by the weak r-process, main r-process,and main s-process components. The main r-process and weak r-process componentcoefficients are almost constants for the stars. Their s-process element abundances come fromthe pollution of low-mass AGB stars. Although the stars of M22have low metallicities, theirs-process abundance pattern has reached to the main s-process pattern in the solar system. Thecomponent coefficient trends of s-process and r-processes in M22are different obviously. Theincrease trend of the s-process component coefficients with [Fe/H] means that thecontributions of main s-process to the abundances of M22stars gradually increase, which canbe explained by the longer lifetime of low-mass AGB stars. This is maybe the results ofinter-evolution.Using five components, we decompose the abundances of higher metallicities stars in theMilky Way and obtain the trends of individual components with metallicities. Using the samemethod, we study the stellar abundances of Fornax dwarf galaxy and compare the results withthose of the Milky Way stars with similar metallicities. Both observational results and calculated results are significant evidences that the IMF of the Fornax dSph is bottom heavierthan that of the Milky Way.