Light-Element Abundances of Giant Stars in the Globular Cluster M71 (NGC 6838)

TL;DR

This study investigates the chemical abundances of light elements in giant stars of the globular cluster M71 to understand star-to-star variations and their implications for cluster formation models.

Contribution

It provides detailed measurements of O, Na, Al, and Fe in M71 giants, revealing a lack of strong Na-Al correlation similar to more metal-rich clusters, challenging existing formation theories.

Findings

M71 stars show no strong Na-Al correlation.

Stars exhibit a narrow [Al/Fe] range.

Results contrast with more metal-poor GCs.

Abstract

Aluminum is the heaviest light element displaying large star--to--star variations in Galactic globular clusters (GCs). This element may provide additional insight into the origin of the multiple populations now known to be a common place in GCs, and also the nature of the first-generation stars responsible for a cluster's chemical inhomogeneities. In a previous analysis we found that, unlike more metal-poor GCs, 47 Tuc did not exhibit a strong Na-Al correlation, which motivates a careful study of the similar metallicity but less massive GC M71. We present chemical abundances of O, Na, Al, and Fe for 33 giants in M71 using spectra obtained with the WIYN-Hydra spectrograph. Our spectroscopic analysis finds that, similar to 47 Tuc and in contrast with more metal-poor GCs, M71 stars do not exhibit a strong Na-Al correlation and span a relatively narrow range in [Al/Fe], which are characteristics that GC formation models must reproduce.