The Peculiar Chemical Inventory of NGC 2419 -- An Extreme Outer Halo "Globular Cluster"

TL;DR

This study investigates the chemical composition of NGC 2419, an outer halo globular cluster, revealing one peculiar star with unusual element ratios and finding that most stars have typical inner halo cluster abundances.

Contribution

It provides detailed high-resolution spectroscopic analysis of NGC 2419's stars, highlighting a unique star and comparing overall abundance patterns to inner halo clusters.

Findings

One star shows extremely low Mg/Fe and high K/Fe ratios.

Most stars exhibit typical inner halo globular cluster abundances.

NGC 2419's overall properties are similar to inner halo clusters.

Abstract

NGC 2419 is a massive outer halo Galactic globular cluster whose stars have previously been shown to have somewhat peculiar abundance patterns. We have observed seven luminous giants that are members of NGC 2419 with Keck/HIRES at reasonable SNR. One of these giants is very peculiar, with an extremely low [Mg/Fe] and high [K/Fe] but normal abundances of most other elements. The abundance pattern does not match the nucleosynthetic yields of any supernova model. The other six stars show abundance ratios typical of inner halo Galactic globular clusters, represented here by a sample of giants in the nearby globular cluster M30. Although our measurements show that NGC 2419 is unusual in some respects, its bulk properties do not provide compelling evidence for a difference between inner and outer halo globular clusters.