J/A+A/688/A72 3D non-LTE Mg abundance (Matsuno+, 2024)
3D non-local thermodynamic equilibrium magnesium abundances reveal a distinct
halo population.
Matsuno T., Amarsi A.M., Carlos M., Nissen P.E.
<Astron. Astrophys. 688, A72 (2024)>
=2024A&A...688A..72M 2024A&A...688A..72M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, dwarfs ; Abundances
Keywords: stars: abundances - stars: atmospheres - Galaxy: halo
Abstract:
Magnesium is one of the important elements in stellar physics as an
electron donor and in Galactic Archaeology as a discriminator of
different stellar populations. However, previous studies of Mgi and
Mgii lines in metal-poor benchmark stars have flagged problems with
magnesium abundances inferred from one-dimensional (1D), hydrostatic
models of stellar atmospheres, both with or without the local
thermodynamic equilibrium (LTE) approximation.We here present 3D
non-LTE calculations for magnesium in FG-type dwarfs, and provide
corrections for 1D LTE abundances. The 3D non-LTE corrections reduce
the ionisation imbalances in the benchmark metal-poor stars HD84937
and HD140283 from -0.16dex and -0.27dex in 1D LTE, to just
-0.02dex and -0.09dex respectively.We then applied our abundance
corrections to 1D LTE literature results for stars in the thin disc,
thick disc, alpha-rich halo, and alpha-poor halo. We find that the 3D
non-LTE results show a richer substructure in [Mg/Fe]-[Fe/H] in the
alpha-poor halo, revealing two subpopulations at the metal-rich end.
These two subpopulations are also separated in kinematics, supporting
the astrophysical origin of the separation. While the more
magnesium-poor subpopulation is likely to be debris from a massive
accreted galaxy, Gaia-Enceladus, the other subpopulation may be
related to a previous identified group of stars, called Eos. The
presence of additional separation in [Mg/Fe] suggests that previous Mg
abundance measurements may have been limited in the precision by the
1D and LTE approximations, highlighting the importance of 3D non-LTE
modelling.
Description:
We present 1D non-LTE and 3D non-LTE corrections for Mg I and Mg II
lines of FG-dwarfs as a function of Teff, logg, [Mg/H], and
microturbulence. The 3D abundances are computed with a 3D non-LTE
code, Balder, based on Stagger-grid.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 75 2646 Abundance corrections
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Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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5- 8 I4 K Teff Effective temperature
17- 20 F4.2 [cm/s2] logg Surface gravity
23- 26 F4.2 --- A(Mg) Mg abundance
35- 37 F3.1 km/s vmic Microturbulence velocity
39- 53 A15 --- line Wavelength of the line
59- 64 F6.3 --- 1N-1L 1D non-LTE - 1D LTE abundance correction
70- 75 F6.3 --- 3N-1L 3D non-LTE - 1D LTE abundance correction
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History:
From Tadafumi Matsuno, matsuno(at)uni-heidelberg.de
Acknowledgements:
We thank Per Jonsson and Henrik Hartman (Malmo Universitet) for
useful discussions about the MgI oscillator strengths.
(End) Patricia Vannier [CDS] 29-May-2024