The AMBRE Project: Origin and evolution of sulfur in the Milky Way

Abstract

[Abstract]: Context. Sulfur is a volatile chemical element that plays an important role in tracing the chemical evolution of the Milky Way and external galaxies. However, its nucleosynthesis origin and abundance variations in the Galaxy are still unclear because the number of available stellar sulfur abundance measurements is currently rather small.

Aims. The goal of the present article is to accurately and precisely study the sulfur content of large number of stars located in the solar neighbourhood.

Methods. We use the parametrisation of thousands of high-resolution stellar spectra provided by the AMBRE Project, and combine it with the automated abundance determination GAUGUIN to derive local thermodynamic equilibrium sulfur abundances for 1855 slow-rotating FGK-type stars. This is the largest and most precise catalogue of sulfur abundances published to date. It covers a metallicity domain as high as ∼2.5 dex starting at [M/H] ∼ −2.0 dex.

Results. We find that the sulfur-to-iron abundances ratio is compatible with a plateau-like distribution in the metal-poor regime, and then starts to decrease continuously at [M/H] ∼ −1.0 dex. This decrease continues towards negative values for supersolar metallicity stars as recently reported for magnesium and as predicted by Galactic chemical evolution models. Moreover, sulfur-rich stars having metallicities in the range [ − 1.0, −0.5] have very different kinematical and orbital properties with respect to more metal-rich and sulfur-poor ones. Two disc components, associated with the thin and thick discs, are thus seen independently in kinematics and sulfur abundances. The sulfur radial gradients in the Galactic discs have also been estimated. Finally, the enrichment in sulfur with respect to iron is nicely correlated with stellar ages: older metal-poor stars have higher [S/M] ratios than younger metal-rich ones.

Conclusions. This work has confirmed that sulfur is an α-element that could be considered to explore the Galactic populations properties. For the first time, a chemo-dynamical study from the sulfur abundance point of view, as a stand-alone chemical element, is performed.