Abstract
Context. The abundance of α-elements provides an important fossil signature in Galactic archaeology to trace the chemical evolution of the different disc populations. High-precision chemical abundances are crucial to improving our understanding of the chemodynamical properties present in the Galaxy. However, deriving precise abundance estimations in the metal-rich disc ([M/H] > 0 dex) is still challenging. Aims. The aim of this paper is to analyse different error sources affecting magnesium abundance estimations from optical spectra of metal-rich stars. Methods. We derived Mg abundances for 87522 high-resolution spectra of 2210 solar neighbourhood stars from the AMBRE Project, and selected the 1172 best parametrised stars with more than four repeated spectra. For this purpose, the GAUGUIN automated abundance estimation procedure was employed. Results. The normalisation procedure has a strong impact on the derived abundances, with a clear dependence on the stellar type and the line intensity. For non-saturated lines, the optimal wavelength domain for the local continuum placement should be evaluated using a goodness-of-fit criterion, allowing mask-size dependence with the spectral type. Moreover, for strong saturated lines, applying a narrow normalisation window reduces the parameter-dependent biases of the abundance estimate, increasing the line-to-line abundance precision. In addition, working at large spectral resolutions always leads to better results than at lower ones. The resulting improvement in the abundance precision makes it possible to observe both a clear thin-thick disc chemical distinction and a decreasing trend in the magnesium abundance even at supersolar metallicities. Conclusions. In the era of precise kinematical and dynamical data, optimising the normalisation procedures implemented for large spectroscopic stellar surveys would provide a significant improvement to our understanding of the chemodynamical patterns of Galactic populations.
Highlights
Disentangling the chemodynamical signatures present in the disc’s stellar populations is essential to unveiling the formation and evolution of the Milky Way
We present a detailed spectroscopic analysis of the Mg abundance estimation for a sample of 2210 FGKtype stars in the solar neighbourhood observed and parametrised at high spectral resolution within the context of the AMBRE Project
We only considered the HARPS spectra sample due to the high spectral resolution (R ∼ 115 000, Mayor et al 2003) and to avoid biases among the different spectrographs included in the AMBRE Project
Summary
Disentangling the chemodynamical signatures present in the disc’s stellar populations is essential to unveiling the formation and evolution of the Milky Way. The abundance of [α/Fe] is used as a good chronological proxy This is due to the timescale delay between core-collapse supernovae (Type II SNe) of the most massive stars (M 8 M ), which enrich the ISM with α-elements predominantly, and Type Ia SNe, which release mainly iron-peak elements (Matteucci & Greggio 1986). Both high- and low-α sequences seem to overlap at supersolar metallicites, showing a flat trend for most α-process elements (not expected by chemical evolution models) being impossible to chemically identify to which stellar population they belong. Different features of the disc [α/Fe] abundances as the intermediate α populations at high metallicities (Adibekyan et al 2012; Mikolaitis et al 2017) and the gap between these stars and the high-α metal-poor population (Adibekyan et al 2012; Gazzano et al 2013), are still matter of debate
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