Through thick and thin: Kinematic and chemical components in the solar neighbourhood

Abstract

We search for chemically distinct stellar components in the solar neighbourhood using a compilation of published data. Extending earlier work, we show that when the abundances of Fe, α elements and the r-process element Eu are considered together, stars separate neatly into two groups that delineate the traditional thin and thick disc components of the Milky Way. The group akin to the thin disc is traced by stars with [Fe/H] > -0.7 and [α/Fe] < 0.2. The thick disc-like group overlaps the thin disc in [Fe/H] but has higher abundances of α elements and Eu. Stars in the range -1.5 < -1.5. These results suggest that it may be possible to define the main dynamical components of the solar neighbourhood using only their chemistry, an approach with a number of interesting consequences. With such definition, the kinematics of thin disc stars is found to be independent of metallicity: their average rotation speed remains roughly constant in the range -0.7