Chemical constraints on the formation of the Galactic thick disk

TL;DR

This study analyzes high-resolution spectra of 703 nearby F and G dwarf stars to investigate the chemical and age properties of the Galactic thin and thick disks, revealing differences in abundance trends, age-metallicity relations, and classification biases.

Contribution

It provides detailed chemical abundance analysis and compares kinematic and age-based classifications, highlighting biases and the extent of the thick disk reaching solar metallicities.

Findings

Thick disk stars are more α-enhanced than thin disk stars at the same metallicity.

The thick disk extends to at least solar metallicities.

The thin disk's age-metallicity relation shows no gradient.

Abstract

We highlight some results from our detailed abundance analysis study of 703 kinematically selected F and G dwarf stars in the solar neighbourhood. The analysis is based on spectra of high-resolution (R=45000 to 110000) and high signal-to-noise (S/N=150 to 300). The main findings include: (1) at a given metallicity, the thick disk abundance trends are more $\alpha$-enhanced than those of the thin disk; (2) the metal-rich limit of the thick disk reaches at least solar metallicities; (3) the metal-poor limit of the thin disk is around [Fe/H]=-0.8; (4) the thick disk shows an age-metallicity gradient; (5) the thin disk does {\it not} show an age-metallicity gradient; (6) the most metal-rich thick disk stars at [Fe/H]=0 are significantly older than the most metal-poor thin disk stars at [Fe/H]=-0.7; (7) based on our elemental abundances we find that kinematical criteria produce thin and thick disk stellar samples that are biased in the sense that stars from the low-velocity tail of the thick disk are classified as thin disk stars, and stars from the high-velocity tail of the thin disk are classified as thick disk stars; (8) age criteria appears to produce thin and thick disk stellar samples with less contamination.