A stellar endgame -- the born-again Sakurai's object

TL;DR

This paper reports on the rapid chemical evolution of Sakurai's object, a star undergoing a final helium-shell flash, revealing hydrogen deficiency, enrichment in s-process elements, and similarities to R Coronae Borealis stars.

Contribution

It provides observational evidence of the star’s rapid surface chemical changes during a born-again AGB phase, supporting the final He-shell flash hypothesis.

Findings

Hydrogen abundance decreased by 0.7 dex in five months.

Surface enriched in Li, Sr, Y, Zr during observations.

Low C12/C13 ratio indicates hydrogen ingestion.

Abstract

The surface chemical composition of this remarkable star shows that it is hydrogen-deficient, carbon-rich and enriched in the light s-process elements. Spectra taken in May and October 1996 indicate a decrease in the surface hydrogen abundance by 0.7 dex in five months along with an increase in the abundances of Li, Sr, Y and Zr. The abundance changes are in agreement with the hypothesis of the star being a rapidly evolving ``born-again'' AGB star experiencing a final He-shell flash, similar to FG Sge. The C^12/C^13 ratio in October is very low, also suggesting hydrogen ingestion. By chemical composition, Sakurai's object resembles the R Coronae Borealis (R CrB) stars.