Old open clusters as key tracers of Galactic chemical evolution. I. Fe abundances in NGC 2660, NGC 3960, and Berkeley 32

TL;DR

This study uses high-resolution spectra to measure the metallicity of three old open clusters, revealing their chemical compositions and contributing to understanding the Galactic disk's chemical evolution.

Contribution

First high-resolution metallicity measurements for Be 32 and NGC 2660, providing homogeneous data to study Galactic chemical gradients.

Findings

NGC 3960 and NGC 2660 have near-solar metallicity.

Be 32 has a sub-solar metallicity of [Fe/H] = -0.29.

Results aid in mapping the Galactic metallicity gradient.

Abstract

We obtained high-resolution UVES/FLAMES observations of a sample of nine old open clusters spanning a wide range of ages and Galactocentric radii. The goal of the project is to investigate the radial metallicity gradient in the disk, as well as the abundance of key elements (alpha and Fe-peak elements). In this paper we present the results for the metallicity of three clusters: NGC 2660 (age ~1 Gyr, Galactocentric distance of 8.68 kpc), NGC 3960 (~ 1 Gyr, 7.80 kpc), and Be 32 (~6-7 Gyr, 11.30 kpc). For Be 32 and NGC 2660, our study provides the first metallicity determination based on high-resolution spectra. We performed equivalent width analysis with the spectral code MOOG, which allows us to define a metallicity scale and build a homogeneous sample. We find that NGC 3960 and NGC 2660 have a metallicity that is very close to solar ([Fe/H]=+0.02 and +0.04, respectively), while the older Be 32 turns out to have [Fe/H]=$-$0.29.