The relation between chemical abundances and kinematics of the Galactic disc with RAVE

Abstract

Aims. We study the relations between stellar kinematics and chemical abundances of a large sample of RAVE giants in search of the selection criteria needed for disentangling different Galactic stellar populations, such as thin disc, thick disc and halo. A direct comparison between the chemo-kinematic relations obtained with our medium spectroscopic resolution data and those obtained from a high-resolution sample is carried out with the aim of testing the robustness of the RAVE data.

Methods. We selected a sample of 2167 giant stars with signal-to-noise per spectral measurements above 75 from the RAVE chemical catalogue and followed the analysis performed by Gratton and colleagues on 150 subdwarf stars spectroscopically observed at high resolution. We then used a larger sample of 9131 giants (with signal-to-noise above 60) to investigate the chemo-kinematical characteristics of our stars by grouping them into nine subsamples with common eccentricity (e) and maximum distance achieved above the Galactic plane (Z(max)).

Results. The RAVE kinematical and chemical data proved to be reliable by reproducing the results by Gratton et al. obtained with high-resolution spectroscopic data. We successfully identified three stellar populations that could be associated with the Galactic thin disc, a dissipative component composed mostly of thick-disc stars, as well as a component comprised of halo stars (presence of debris stars cannot be excluded). Our analysis, based on the e-Z(max) plane combined with additional orbital parameters and chemical information, provides an alternative way of identifying different populations of stars. In addition to extracting canonical thick-and thin-disc samples, we find a group of stars in the Galactic plane (Z(max) < 1 kpc and 0.4 < e < 0.6) that show homogeneous kinematics but differ in their chemical properties. We interpret this as a clear sign that some of these stars have experienced the effects of heating and/or radial migration, which have modified their original orbits. The accretion origin of such stars cannot be excluded.