Vol. 562
In section 5. Galactic structure, Stellar clusters and populations

Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood

by T. Bensby, S. Feltzing, M.S. Oey, A&A 562, A71


This paper presents measurements of the chemical abundances (O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, and Ba) and age determinations of 714 nearby Galactic F and G dwarf and subgiant stars, and uses them to explore the detailed properties of the Galactic stellar disk. The high signal-to-noise and high spectral resolution observations come from a range of world-wide spectrographs and the determination of stellar parameters and elemental abundances are based on a standard 1D LTE analysis using equivalent width measurements. The accurate results show two main Galactic disk populations that overlap in metallicity, an old, alpha-enhanced population and a younger, less alpha-enhanced population. The alpha-enhanced population has orbital parameters that suggest an origin in the inner Galactic disk, whilst the low-alpha stars are more consistent with the outer Galactic disk. Thus, this study reveals a Galactic thick disk that is more centrally concentrated than previously thought, and a thin disk that is much more extended than the thick disk. This study also includes the Hercules stream and the Arcturus moving group, and finds that their detailed age and abundance properties are inconsistent with disrupted star clusters or other extragalactic accretion remnants from ancient mergers, and that they are both more likely to be dynamical features originating within the Galaxy.