Elemental abundances of intermediate age open cluster NGC 3680

TL;DR

This study provides a detailed chemical abundance analysis of the open cluster NGC 3680, revealing unique s- and r-process element patterns and Na enhancement in giants, offering insights into nucleosynthesis processes in intermediate age clusters.

Contribution

First detailed abundance analysis of NGC 3680 including s- and r-process elements, highlighting unusual element patterns and Na enhancement in giants.

Findings

Significant Na enhancement in giants compared to dwarfs.

Heavy s-process elements increase with atomic number, contrary to models.

R-process contribution significant for La and Nd in the cluster.

Abstract

We present a new abundance analysis of the intermediate age Galactic open cluster NGC 3680, based on high resolution, high signal-to-noise VLT/UVES spectroscopic data. Several element abundances are presented for this cluster for the first time, but most notably we derive abundances for the light and heavy s-process elements Y, Ba, La, and Nd. The serendipitous measurement of the rare-earth r-process element Gd is also reported. This cluster exhibits a significant enhancement of Na in giants as compared to dwarfs, which may be a proxy for an O to Na anti-correlation as observed in Galactic globular clusters but not open clusters. We also observe a step-like enhancement of heavy s-process elements towards higher atomic number, contrary to expectations from AGB nucleosynthesis models, suggesting that the r-process played a significant role in the generation of both La and Nd in this cluster