Issue |
A&A
Volume 688, August 2024
|
|
---|---|---|
Article Number | A72 | |
Number of page(s) | 8 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/202450057 | |
Published online | 06 August 2024 |
3D non-local thermodynamic equilibrium magnesium abundances reveal a distinct halo population★
1
Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg,
Mönchhofstraße 12–14,
69120
Heidelberg,
Germany
e-mail: matsuno@uni-heideberg.de
2
Kapteyn Astronomical Institute, University of Groningen,
Landleven 12,
9747 AD
Groningen,
The Netherlands
3
Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University,
Box 516,
751 20
Uppsala,
Sweden
e-mail: anish.amarsi@physics.uu.se
4
Department of Physics and Astronomy, Aarhus University,
Ny Munkegade 120,
8000
Aarhus C,
Denmark
Received:
21
March
2024
Accepted:
15
May
2024
Magnesium is one of the most important elements in stellar physics as an electron donor; in Galactic archaeology, magnesium serves to distinguish different stellar populations. However, previous studies of Mg I and Mg II lines in metal-poor benchmark stars indicate that magnesium abundances inferred from one-dimensional (1D), hydrostatic models of stellar atmospheres, both with and without the local thermodynamic equilibrium (LTE) approximation, can be problematic. Here, we present three-dimensional (3D) non-LTE calculations for magnesium in FG-type dwarfs and provide corrections for 1D-LTE abundances. 3D non-LTE corrections reduce the ionisation imbalances in the benchmark metal-poor stars HD84937 and HD140283 from −0.16 dex and −0.27 dex in 1D LTE to just −0.02 dex and −0.09 dex, respectively. We applied our abundance corrections to 1D LTE literature results for stars in the thin disc, thick disc, α-rich halo, and α-poor halo. We observed that 3D non-LTE results had a richer substructure in [Mg/Fe] − [Fe/H] in the α-poor halo, revealing two sub-populations at the metal-rich end. These two sub-populations also differ in kinematics, supporting the astro-physical origin of the separation. While the more magnesium-poor sub-population is likely to be debris from a massive accreted galaxy, Gaia-Enceladus, the other sub-population may be related to a previously identified group of stars, called Eos. The additional separation in [Mg/Fe] suggests that previous Mg abundance measurements may have been imprecise due to the 1D and LTE approximations, highlighting the importance of 3D non-LTE modelling.
Key words: stars: abundances / stars: atmospheres / galaxy: halo
The table with abundance corrections is available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A72
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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