A high-resolution spectroscopic search for multiple populations in the 2 Gyr old cluster NGC 1846

TL;DR

This study investigates the chemical composition of stars in the 1.95 Gyr old cluster NGC 1846, finding no evidence of multiple populations but detecting internal carbon abundance variations, contributing to understanding cluster evolution.

Contribution

First detailed abundance analysis of NGC 1846's stars showing no multiple populations at this age, with insights into chemical homogeneity and stellar evolution effects.

Findings

No intrinsic Na and O abundance spread detected.

Significant variation in carbon abundances observed.

Cluster's overall abundance pattern similar to other intermediate-age clusters.

Abstract

We present detailed C, O, Na, Mg, Si, Ca, Ti, V, Fe, Zr, Ba, and Eu abundance measurements for 20 red giant branch (RGB) stars in the LMC star cluster NGC 1846 ([Fe/H] = -0.59). This cluster is 1.95 Gyr old and lies just below the supposed lower age limit (2 Gyr) for the presence of multiple populations in massive star clusters. Our measurements are based on high and low-resolution VLT/FLAMES spectra combined with photometric data from HST. Corrections for non-local thermodynamic equilibrium effects are also included for O, Na, Mg, Si, Ca, Fe and Ba. Our results show that there is no evidence for multiple populations in this cluster based on the lack of any intrinsic star-to-star spread in the abundances of Na and O: we place 95 \% confidence limits on the intrinsic dispersion for these elements of $\leq 0.07$ and $\leq 0.09$ dex, respectively. However, we do detect a significant spread in the carbon abundances, indicating varying evolutionary mixing occurring on the RGB that increases with luminosity. Overall, the general abundance patterns for NGC 1846 are similar to those seen in previous studies of intermediate-age LMC star clusters and field stars.