Study of the abundance features of the metal-poor star HD 94028

TL;DR

This study investigates the origins of element abundances in the metal-poor star HD 94028, revealing that the weak r-process explains the observed light element ratios better than other processes.

Contribution

It introduces an abundance decomposition method to identify the astrophysical sources of elements in HD 94028, emphasizing the role of the weak r-process for light neutron-capture elements.

Findings

Weak r-process explains Ge, As, Se abundance ratios.

Primary process of massive stars dominates light and iron-group elements.

i-process is unnecessary for explaining light neutron-capture elements in this star.

Abstract

Recent work has found that the metal-poor star HD 94028 shows interesting abundance features. The s-process material (e.g., Ba, La, Ce, and Pb) and r-process material (e.g., Eu, Os, Pt) are mildly overabundant while the element C is not enhanced. However, the observed supersolar ratio [As/Ge](= $0.99 \pm 0.23$) and subsolar ratio [Se/As](= $-0.16 \pm 0.22$) could not be fitted by the combination of s- and r-process abundances. In this work, adopting the abundance decomposition method, we investigate the astrophysical origins of the elements in this star. We find that the primary process of massive stars dominates the production of the light elements and iron-group elements. The lighter neutron-capture elements from Ge to Te mainly come from the weak r-process. The elements from Ba to Pb are synthesized dominantly by the main s- and main r-process. The observed abundance features of Ge, As, and Se in HD 94028 are mainly produced by the weak r-process, which possesses the features of the supersolar ratio [As/Ge] and subsolar ratio [Se/As]. Because Ge is not synthesized solely by the neutron-capture process, As should be the lightest neutron-capture element. Although the i-process has been suggested in several astrophysical environments, it should be superfluous to explaining the abundances of the lighter neutron-capture elements in HD 94028.