Chemical composition of evolved stars in the young open clusters NGC 4609 and NGC 5316

TL;DR

This study presents the first high-resolution spectral analysis of evolved stars in young open clusters NGC 4609 and NGC 5316, examining elemental abundances to understand stellar mixing processes and Galactic chemical evolution.

Contribution

It provides new observational data on elemental abundances in evolved stars of young clusters, testing models of stellar mixing and Galactic chemical evolution.

Findings

12C/13C and C/N ratios align with mixing models including thermohaline and rotation effects.

Clusters follow thin disk alpha-element trends.

NGC 4609's neutron-capture elements reflect its thin disk origin, NGC 5316 shows slight enrichment.

Abstract

High-resolution spectral analysis is performed for the first time in evolved stars of two young open clusters: NGC 4609 and NGC 5316, of about 80 and 100 Myr in age, respectively, and turn-off masses above 5 Msun. Stellar evolution models predict an extra-mixing event in evolved stars, which follows the first dredge-up and happens later on the red giant branch. However, it is still not understood how this process affects stars of different masses. In this study, we determine abundances of the mixing sensitive elements carbon and nitrogen, carbon isotope 12C/13C ratios, as well as 20 other elements produced by different nucleosynthetic processes (O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Y, Zr, Ba, La, Ce, Pr, Nd, and Eu). We compared our results with the latest theoretical models of evolutionary mixing processes. We find that the obtained 12C/13C and C/N ratios and [Na/Fe] agree quite well with the model which takes into account thermohaline- and rotation-induced mixing but within error limits also agree with the standard first dredge-up model. Comparison of oxygen, magnesium and other alpha-elements with theoretical models of Galactic chemical evolution revealed that both clusters follow the thin disk alpha-element trends. Neutron-capture element abundances in NGC 4609 are apparently reflecting its birthplace in the thin disk, while NGC 5316 has marginally higher abundances, which would indicate its birthplace in an environment more enriched with neutron-capture elements.