Medium-resolution s-process Element Survey of 47 Tuc giant stars

TL;DR

This study analyzes medium-resolution spectra of 97 giant stars in 47 Tuc to investigate element abundances and their correlations, revealing a homogeneous chemical composition and potential evidence of a second star formation era within the cluster.

Contribution

It provides the first detailed analysis of multiple element abundances in 47 Tuc giants using medium-resolution spectra, highlighting correlations and abundance homogeneity.

Findings

Na abundance correlates with CN excess (deltaC)

Elemental abundances (Fe, Si, Ca, Zr, Ba) are homogeneous

No overall metallicity variation with deltaC

Abstract

Medium-resolution (R~6,500) spectra of 97 giant stars in the globular cluster 47 Tucanae (47 Tuc) have been used to derive the C and N abundance sensitive index, deltaC, and to infer abundances of several key elements, Fe, Na, Si, Ca, Zr and Ba for a sample of 13 of these stars with similar Teff and log g. These stars have stellar properties similar to the well-studied 47 Tuc giant star, Lee 2525, but with a range of CN excess (deltaC) values which are a measure of the CN abundance. The deltaC index is shown to be correlated with Na abundance for this sample, confirming previous studies. The Fe, Ca, Si and the light- and heavy-s process (slow neutron capture) elements, Zr and Ba respectively, have a narrow range of abundance values in these stars, indicative of a homogeneous abundance within this population of stars. The constancy of many element abundances (Fe, Si, Ca, Zr, Ba) and the deltaC and Na abundance correlation could imply that there has been a second era of star formation in this cluster that has revealed the products of CNO cycle burning via hot bottom burning (depletion of C, enhancement of N and the production of Na for high deltaC population). But there is no overall metallicity change across the range of deltaC values at a given position in the HR diagram that has been seen in some other globular clusters.