A First Constraint on the Thick Disk Scale Length: Differential Radial Abundances in K Giants at Galactocentric Radii 4, 8, and 12 kpc

Understand

Based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan telescopes we present detailed elemental abundances for 20 red giant stars in the outer Galactic disk, located at Galactocentric distances between 9 and 13 kpc.

• The outer disk sample is complemented with samples of red giants from the inner Galactic disk and the solar neighbourhood, analysed using identical methods.
• 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.