两颗CEMP-s视单星化学元素的天体物理来源研究

Study of the Astrophysical Origins of Chemical Elements in Two Apparently-single CEMP-s Stars

CS30301–015和HE1045+0226是两颗C元素和s-过程元素均超丰的贫金属(CEMP-s)星.视向速度观测发现这两颗星可能为单星.采用叠加与分解的方法探究这两颗星化学元素的天体物理来源能够为更好地理解银河系早期化学演化提供线索.计算结果表明:这两颗星的轻元素和Fe族元素主要产生于大质量星的primary过程.对于CS 30301–015,中子俘获元素主要来自AGB (Asymptotic Giant Branch)星中的主要s-过程. Pb的显著超丰主要归因于主要s-过程的贡献(约占Pb观测丰度的99.8%).需要更多的视向速度观测来确定这两颗星的轨道特征.对于HE 1045+0226, 56≤Z (质子数)≤62的重中子俘获元素主要来源于主要s-过程;Eu主要来源于主要r-过程.而轻中子俘获元素Y和Zr主要来自快速自转大质量星的primary弱s-过程,这一核合成过程对HE 1045+0226的Y和Zr丰度的贡献分别约为69.8%和67.6%.这从观测的角度证明弱s-过程能够在贫金属环境下发生.

CS 30301–015 and HE 1045+0226 are two metal-poor stars which show overabundance of both C and s-process elements(i.e., CEMP-s stars). The radial velocity observations suggest that these two CEMP-s stars have constant radial velocities and suggested that CS 30301–015 and HE 1045+0226 could be single stars. Study of the astrophysical origins of chemical elements in the two apparently-single CEMP-s stars can provide useful clues for better understanding the chemical evolution of the early Galaxy. Based on the superposition and decomposition calculations, we investigated the astrophysical origins of chemical elements in the two sample stars. We found that the lighter and Fe-group elements of these two sample stars are mainly produced by primary process in massive stars. For CS 30301–015, the neutron-capture elements dominantly originate from the main s-process in Asymptotic Giant Branch(AGB) stars. The high Pb abundance can be explained by the contribution of main s-process. The contributed fraction of main s-process to Pb is about 99.8%. More radial-velocity observations are needed to confirm the orbital features of this sample star. While for the other sample star HE 1045+0226, the heavier neutron-capture elements with 56≤Z≤62 are mainly produced by main s-process and Eu mainly originate from main r-process, Z is the proton number. However, the lighter neutron-capture elements Y and Zr mainly come from the primary weak s-process occurring in fast rotation massive stars. The contributed fractions of the primary weak s-process to Y and Zr abundances of HE 1045+0226 are about 69.8% and 67.6%, respectively. This suggests that the apparently-single CEMP-s star HE 1045+0226 should have the footprints of primary weak s-process. The conclusions prove that weak s-process could occur in metal-poor environments.