Detection of Enhanced Germanium in a New Cool Extreme Helium Star A 980: Insights and Implications

TL;DR

This study identifies germanium in a cool extreme helium star, A 980, marking the first detection of Ge lines in such stars and providing insights into nucleosynthesis processes in EHe stars.

Contribution

First detection of germanium lines in an extreme helium star, revealing germanium synthesis and nucleosynthesis signatures in A 980.

Findings

Germanium overabundance in A 980's atmosphere

Detection of s-process element enhancement

Evidence of nucleosynthesis processes in EHe stars

Abstract

A fine abundance analysis of a recently discovered hydrogen-deficient carbon (HdC) star, A 980, is presented. Based on the observed high-resolution optical spectrum, we ascertain that A 980 is a cool extreme helium (EHe) star and not an HdC. Singly-ionized germanium Ge II lines are identified in A 980's optical spectrum. These are the first-ever detections of germanium lines in an EHe's observed spectrum, and provide the first measurements of germanium abundance in an EHe star. The overabundance of germanium in A 980's atmosphere provides us with evidence for the synthesis of germanium in EHe stars. Among the known cool EHe stars, A 980 exhibits a maximum enhancement of the s-process elements based on significant number of transitions. The measured elemental abundances reveal signs of H-burning, He-burning, and specifically the nucleosyntheses of the key elements: Ge, Sr, Y, Zr, and Ba. The nucleosyntheses of these key elements are discussed in light of asymptotic giant branch evolution and the expectation from the accretion of an He white dwarf by a C-O white dwarf or by a neutron star.