A comparative study of two 47 Tuc giant stars with different s-process enrichment

TL;DR

This study compares two stars in 47 Tuc with different s-process element enrichments, suggesting that some stars were enriched by mass transfer from AGB stars, revealing complex nucleosynthetic histories within the cluster.

Contribution

It provides detailed abundance analyses of two 47 Tuc stars with contrasting s-process enrichments and links their patterns to AGB star nucleosynthesis, highlighting multiple enrichment sources.

Findings

Star Lee 4710 has the highest La abundance in 47 Tuc.

Lee 4710's pattern matches a 1.3 solar mass AGB star yield.

Several other 47 Tuc stars show signs of enrichment by more massive AGB stars.

Abstract

Here we aim to understand the origin of 47 Tuc's La-rich star Lee 4710. We report abundances for O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, Zn, Y, Zr, Ba, La, Ce, Pr, Nd, and Eu, and present a detailed abundance analysis of two 47 Tuc stars with similar stellar parameters but different slow neutron-capture (s-)process enrichment. Star Lee 4710 has the highest known La abundance ratio in this cluster ([La/Fe] = 1.14), and star Lee 4626 is known to have normal s-process abundances (e.g., [Ba/Eu]$<0$). The nucleosynthetic pattern of elements with Z$\gtrsim$56 for star Lee 4710 agrees with the predicted yields of a $1.3M_{\odot}$ asymptotic giant branch (AGB) star. Therefore, Lee 4710 may have been enriched by mass transfer from a more massive AGB companion, which is compatible with its location far away from the center of this relatively metal-rich ([Fe/H]$\sim-0.7$) globular cluster. A further analysis comparing the abundance pattern of Lee 4710 with data available in the literature reveals that nine out of the $\sim200$ 47 Tuc stars previously studied show strong s-process enhancements that point towards later enrichment by more massive AGB stars.