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

摘要

© 2022CS 30301–015 and HE 1045+0226 are two metal-poor stars which show overabundances of both C and s-process elements (i.e., (Carbon-Enhanced Metal-Poor) CEMP-s stars). The radial-velocity observations suggest that these two CEMP-s stars appear to be single stars. Study of the astrophysical origins of chemical elements in the two apparently-single CEMP-s stars can provide useful information for better understanding the chemical evolution of the early Galaxy. Based on the abundance superposition and decomposition calculations, we investigate the astrophysical origins of chemical elements in the two sample stars. We find that the light and Fe-peak elements of these two sample stars are mainly produced by the primary process in massive stars. For CS 30301–015, the neutron-capture (n-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 abundance 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 n-capture elements with 56≤Z≤62 are mainly produced by main s-process. Eu mainly originates from main r-process. However, the lighter n-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 means that the apparently-single CEMP-s star HE 1045+0226 should have the footprints of primary weak s-process. On the observational side, the results prove that the weak s-process could occur in metal-poor environments.