# Comprehensive abundance analysis of red giants in the open clusters Stock 2, NGC 2168, 6475, 6991 and 7762

## TL;DR

This study provides a detailed chemical abundance analysis of red giants in five open clusters, revealing typical element ratios and sodium enrichment consistent with stellar evolution models, and highlights minor variations in s-process element abundances.

## Contribution

It offers the first comprehensive high-resolution abundance analysis of red giants across multiple open clusters, comparing results with field stars and theoretical predictions.

## Key findings

- Sodium enrichment in giants aligns with first dredge-up predictions.
- Most element ratios match those of field giants and dwarfs.
- Minor overabundance of s-process elements in NGC 6991.

## Abstract

We have analysed high-dispersion echelle spectra ($R = 60000$) of red giant members of five open clusters to derive abundances for many elements from Na to Eu. The [Fe/H] values are $-0.06\pm0.03$ for Stock 2, $-0.11\pm0.03$ for NGC 2168, $-0.01\pm0.03$ for NGC 6475, $0.00\pm0.03$ for NGC 6991 and $-0.07\pm0.03$ for NGC 7662. Sodium is enriched in the giants relative to the abundance expected of main sequence stars of the same metallicity. This enrichment of [Na/Fe] by about $+0.25$ attributed to the first dredge-up is discussed in the light of theoretical predictions and recently published abundance determinations. Abundance ratios [El/Fe] for other elements are with very few exceptions equal to those of field giants and dwarfs, i.e., [El/Fe] $\simeq 0.00$ for [Fe/H] $\sim 0.0$. An exception is the overabundance of La, Ce, Nd and Sm in NGC 6991 but this is consistent with our previous demonstration that the abundances of these $s$-process products vary by about $\pm0.2$ among clusters of the same [Fe/H], a variation found also among field giants and dwarfs.