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.

Spectro-photometric distances to stars: A general purpose Bayesian approach

“…Despite the large scatter and a slight systematic trend, our distances for the same sample of red giant stars studied in Boeche et al (2013a) agree, within the expected uncertainties, with those derived by Binney et al (2014a).…”

“…In each panel the vertical axis shows the absolute distance residuals normalised to the combined uncertainty from both methods, used a slightly different metallicity scale, namely that of the RAVE chemical pipeline instead of the RAVE stellar parameter pipeline, and we handled the α-enhancement differently. Figure 8 shows the comparison of our distance estimates with the distances from Binney et al (2014a) for the giant sample analysed in Boeche et al (2013a). To make this comparison compatible with our approach described in Sect.…”

“…More recently, Binney et al (2014a) presented an improved version of the method. In this section, we use their distances for a high S/N sample containing 9000 giant stars (Boeche et al 2013a) to cross-check the implementation of our method (details in Appendix C). The spectroscopic parameters are taken from the RAVE data release 4 (DR4; Kordopatis et al 2013), the photometry is from 2MASS.…”

“…8. Comparison of our distance estimates against the RAVE DR4 distances from Binney et al (2014a) for the high-S/N sample of Boeche et al (2013a). In each panel the vertical axis shows the absolute distance residuals normalised to the combined uncertainty from both methods, used a slightly different metallicity scale, namely that of the RAVE chemical pipeline instead of the RAVE stellar parameter pipeline, and we handled the α-enhancement differently.…”

“…Our emphasis is therefore on confronting our distance estimates with as many reference samples as possible. A direct comparison with the RAVE distances obtained by Binney et al (2014a) for the high-quality giant sample studied in Boeche et al (2013a) is also provided. In Table 1 we list the main characteristic of the surveys to which we have applied our method.…”