Chemo-dynamic features of super-metal-rich stars

We apply a hierarchical clustering algorithm to group the stars with similar chemical abundances within the complete chemical abundance space. Orbits were integrated using astrometric data from Gaia and radial velocities from Gaia-ESO. Stellar ages were estimated using isochrones and a Bayesian method.

According to their chemical properties, this set of super metal-rich stars can be arranged into five subgroups. Four of them seem to follow a chemical enrichment flow, where nearly all abundances increase in lockstep with Fe. The fifth subgroup shows different chemical characteristics.

All subgroups have the following features: median ages of the order of 7-9 Gyr (with five outlier stars of estimated younger age), Solar or sub-Solar [Mg/Fe] ratios, maximum height from the Galactic plane between 0.5-1.5kpc, low eccentricities (e<~0.2), and a detachment from the expected metallicity gradient with guiding radius (which varies between ~6 to 9kpc for the majority of the stars). The high metallicity of our stars is incompatible with a formation in the Solar neighbourhood.

Their dynamic properties agree with theoretical expectations that these stars travelled from the inner Galaxy due to blurring and, most importantly, to churning. We, therefore, suggest that most of the stars in this population originated in the inner regions of the Milky Way (inner disc and/or the bulge) and later migrated to the Solar neighbourhood. The region from where the stars originated had a complex chemical enrichment history, with contribution from supernovae types Ia and II, and possibly asymptotic giant branch stars as well.