Abundance trends in the inner and outer Galactic disk

TL;DR

This study analyzes elemental abundances in 64 red giant stars across the Galactic disk, revealing differences in the distribution and scale lengths of the thin and thick disks, with implications for Galactic structure.

Contribution

It provides detailed elemental abundance measurements for stars in the inner and outer Galactic disk, highlighting the different scale lengths of the thin and thick disks.

Findings

Thick and thin disk stars coexist in the inner disk.

Only thin disk patterns are found beyond 10 kpc from the Galactic center.

The thick disk has a shorter radial scale length (~2.0 kpc) than the thin disk (~3.8 kpc).

Abstract

Based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan telescopes we present detailed elemental abundances for 64 red giant stars in the inner and outer Galactic disk. For the inner disk sample (4-7 kpc from the Galactic centre) we find that stars with both thin and thick disk abundance patterns are present while for Galactocentric distances beyond 10 kpc, we only find chemical patterns associated with the local thin disk, even for stars far above the Galactic plane. Our results show that the relative densities of the thick and thin disks are dramatically different from the solar neighbourhood, and we therefore suggest that the radial scale length of the thick disk is much shorter than that of the thin disk. A thick disk scale-length of L_{thick}=2.0 kpc, and L_{thin}=3.8 kpc for the thin disk, better match the data.