A new abundance scale for the globular cluster 47 Tuc

TL;DR

This study provides precise chemical abundances for multiple elements in 47 Tuc, revealing its metallicity, chemical homogeneity, and similarities to the Galactic bulge and thick disk, using high-resolution spectroscopy and differential analysis.

Contribution

It introduces a new abundance scale for 47 Tuc based on high-resolution spectroscopy and differential analysis, refining previous metallicity estimates and characterizing its chemical composition.

Findings

Mean LTE [Fe/H] of -0.76 dex, slightly more metal-poor than previous studies.

Chemical element ratios resemble those of the Galactic bulge.

47 Tuc is mostly chemically homogeneous.

Abstract

We present chemical abundances for O, Na, Mg, Al, Si, Ca, Ti and Fe in eight red giants and one turnoff star in the metal rich globular cluster 47 Tuc, based on spectroscopy with the MIKE high resolution spectrograph on the Magellan 6.5-m Clay telescope. A robust line by line differential abundance analysis technique, relative to the K-giant Arcturus, was used to reduce systematic errors from atmospheric and atomic parameters. Our derived mean LTE [Fe/H] of -0.76 +- 0.01 +- 0.04 dex (random and systematic error, respectively) is more metal poor by about 0.1 dex than recent literature results. The chemical element ratios in this nearby globular cluster most closely resemble those of the Galactic bulge, although there is a non-negligible overlap with the composition of thick-disk stars. We find that the [Al/Fe] and [Na/Fe] ratios coincide with the upper boundary of the trends seen in the bulge and thick disk. There is only a small intrinsic scatter in the majority of the abundance ratios, indicating that 47 Tuc is mostly a rather chemically homogeneous system.