Abundances of disk and bulge giants from high-resolution optical spectra -- IV. Zr, La, Ce, Eu

TL;DR

This study compares neutron-capture element abundances in bulge and disk giants using high-resolution spectra, revealing differences in s- and r-process contributions that inform Galactic chemical evolution.

Contribution

It provides a differential analysis of Zr, La, Ce, and Eu abundances in bulge and disk giants, minimizing systematic effects and highlighting population differences.

Findings

Bulge shows higher La abundance than the disk.

Eu/Fe decreases with increasing metallicity, similar to alpha-elements.

Bulge and thick disk have similar [(La+Ce)/Zr] ratios.

Abstract

Stellar mass and metallicity are factors that affect the neutron-capture process. Due to this, the enrichment of the ISM and the abundance of neutron-capture elements vary with time, making them suitable probes for the Galactic chemical evolution. In this work we make a differential comparison of neutron-capture element abundances determined in the local disk(s) and the bulge, focusing on minimising possible systematic effects in the analysis, with the aim of finding possible differences/similarities between the populations. Abundances are determined for Zr, La, Ce and Eu in 45 bulge giants and 291 local disk giants, from high-resolution optical spectra. The abundances are determined by fitting synthetic spectra using the SME-code. The disk sample is separated into thin/thick disk components using a combination of abundances and kinematics. We find flat Zr, La, Ce trends in the bulge, with a $\sim 0.1$ dex higher La abundance compared with the disk, possibly indicating a higher s-process contribution for La in the bulge. [Eu/Fe] decreases with increasing [Fe/H], with a plateau at around [Fe/H] $\sim -0.4$, pointing at similar enrichment as $\alpha$-elements in all populations. We find that the r-process dominated the neutron-capture production at early times both in the disks and bulge. [La/Eu] for the bulge are systematically higher than the thick disk, pointing to either a) a different amount of SN II or b) a different contribution of the s-process in the two populations. Considering [(La+Ce)/Zr], the bulge and the thick disk follow each other closely, suggesting a similar ratio of high/low mass asymptotic giant branch-stars.