Precise abundance analysis of the outer halo globular cluster M 75

TL;DR

This study provides a detailed chemical abundance analysis of 16 red giants in the outer halo globular cluster M75, revealing multiple stellar populations, a slight metallicity spread, and insights into early cluster enrichment.

Contribution

First high-resolution spectroscopic analysis of M75, uncovering multiple populations, chemical abundance patterns, and enrichment history in this outer halo globular cluster.

Findings

Detected clear O-Na anticorrelation indicating multiple generations.

Measured a small metallicity spread of 0.07 dex.

Analyzed r- and s-process elements to understand early enrichment phases.

Abstract

Globular clusters (GCs) are the oldest stellar systems in the Milky Way. Long time considered as simple stellar populations, nowadays we recognize their complex star formation history through precise abundance analysis of a variety of chemical elements in individual cluster members. Although we do not necessarily see clues for multiple populations in all GC colour-magnitude diagrams, all GCs present significant spreads and certain anticorrelations between their light and alpha element abundances. Furthermore, the heavy element abundances in individual stars of the primordial generation and their comparison to halo field stars and dwarf galaxies could provide us with valuable information about the very first stars that could have formed in GCs. M75 is a unique outer halo (galactocentric distance of ~15 kpc) GC with a peculiar Horizontal Branch morphology. Here we present the first abundance measurements of 16 individual red giants from high resolution spectroscopy. The cluster is metal rich ([Fe/H] = -1.17 +/- 0.02), alpha-enhanced, and shows a marginal spread in [Fe/H] of 0.07 dex, typical of most GCs of similar luminosity. The O-Na anticorrelation is clearly visible, showing at least two generations of stars, formed on a short timescale. We also discuss r- and s-process element abundances in the context of the earliest cluster enrichment phases.