A differential chemical abundance scale for the globular cluster M5

TL;DR

This study establishes a differential chemical abundance scale for globular cluster M5 using high-resolution spectroscopy, confirming its typical halo characteristics and demonstrating the method's consistency with previous studies.

Contribution

It introduces a new differential abundance scale for M5, improving consistency and accuracy over previous methods, and validates this approach with high-resolution spectroscopic data.

Findings

Confirmed M5's [Fe/H] at -1.33 dex with high precision.

Reproduced M5's alpha-element enhancement at +0.4 dex.

Most stars show abundance patterns consistent with proton-capture nucleosynthesis.

Abstract

We present LTE chemical abundances for five red giants and one AGB star in the Galactic globular cluster (GC) M5 based on high resolution spectroscopy using the MIKE spectrograph on the Magellan 6.5-m Clay telescope. Our results are based on a line-by-line differential abundance analysis relative to the well-studied red giant Arcturus. The stars in our sample that overlap with existing studies in the literature are consistent with published values for [Fe/H] and agree to within typically 0.04 dex for the alpha-elements. Most deviations can be assigned to varying analysis techniques in the literature. This strengthens our newly established differential GC abundance scale and advocates future use of this method. In particular, we confirm a mean [Fe I/H] of -1.33 +- 0.03 (stat.) +- 0.03 (sys.) dex and also reproduce M5's enhancement in the alpha-elements (O,Mg,Si,Ca,Ti) at +0.4 dex, rendering M5 a typical representative of the Galactic halo. Over-ionization of Fe I in the atmospheres of these stars by non-LTE effects is found to be less than 0.07 dex. Five of our six stars show O-Na-Al-Mg abundance patterns consistent with pollution by proton-capture nucleosynthesis products.