J/A+A/693/A211 Metal-poor stars NLTE abundances of Eu (Guo+, 2025)
Non-local thermodynamic equilibrium (NLTE) abundances of europium (Eu) for a
sample of metal-poor stars in the Galactic halo and metal-poor disk with 1D and
<3D> models.
Guo Y., Storm N., Bergemann M., Lian J., Alexeeva S., Li Y., Ezzeddine R.,
Jeffrey G., Chen X.
<Astron. Astrophys. 693, A211 (2025)>
=2025A&A...693A.211G 2025A&A...693A.211G (SIMBAD/NED BibCode)
ADC_Keywords: Stars, metal-deficient ; Abundances
Keywords: catalogs - Sun: abundances - stars: abundances - stars: evolution -
Galaxy: evolution
Abstract:
As a key to chemical evolutionary studies, the distribution of
elements in galactic provides a wealth of information to understand
the individual star formation histories of galaxies. The r-process is
a complex nucleosynthesis process, and the origin of r-process
elements is heavily debated. Europium (Eu) is viewed as an almost pure
r-process element. Accurate measurements of europium abundances in
cool stars are essential for an enhanced understanding of the
r-process mechanisms.
We measure the abundance of Eu in solar spectra and a sample of
metal-poor stars in the Galactic halo and metal-poor disk, with the
metallicities ranging from -2.4 to -0.5dex, using non-local
thermodynamic equilibrium (NLTE) line formation. We compare these
measurements with Galactic Chemical Evolution (GCE) models to explore
the impact of the NLTE corrections on the contribution of r-process
site in Galactic chemical evolution.
In this work, we used NLTE line formation, as well as one-dimensional
(1D) hydrostatic and spatial averages of three-dimensional
hydrodynamical (<3D>) model atmospheres to measure the abundance of Eu
based on both the EuII 4129Å and EuII 6645Å lines for solar
spectra and metal-poor stars.
We find that for EuII 4129Å line the NLTE modeling leads to higher
(0.04dex) solar Eu abundance in 1D and higher (0.07dex) in <3D> NLTE
while NLTE modeling leads to higher (0.01dex) solar Eu abundance in 1D
and lower (0.03dex) in <3D> NLTE for EuII 6645Å line. Although the
NLTE corrections for the EuII λ 4129Å and EuII λ
6645Å lines are opposite, the discrepancy between the abundances
derived from these individual lines reduces after applying NLTE
corrections, highlighting the critical role of NLTE abundance
determinations. By comparing these measurements with Galactic chemical
evolution (GCE) models, we find that the amount of NLTE correction
does not require significant change of the parameters for Eu
production in GCE models.
Description:
The wavelength range for some of our stars does not include the EuII
4129Å line, and in some cases, both the EuII 4129Å and EuII
6645Å lines are blended or very weak. Therefore, the results
presented below are only for the spectra that were well fitted with a
total of 164 stars having metallicities ranging from -2.4 to -0.5dex.
However, the <3D> grid covers a smaller range of atmospheric
parameters (Magic et al., 2013A&A...557A..26M 2013A&A...557A..26M, Cat. J/A+A/557/A26,
2013A&A...560A...8M 2013A&A...560A...8M, Cat, J/A+A/560/A8) and, thus, only a small
proportion of our sample of stars was fitted with these models.
Therefore, our results are only based on the results of the 1D. All
the best fitting results are provide in Table 3 for EuII 4129Å and
Table 4 for EuII 6645Å .
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 58 37 Results of Eu abundance based on
EuII 4129Å line
table4.dat 58 144 Results of Eu abundance based on
EuII 6645Å line
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See also:
J/A+A/557/A26 : STAGGER-grid of 3D stellar models. I. (Magic+, 2013)
J/A+A/560/A8 : STAGGER-grid of 3D stellar models. II. (Magic+, 2013)
Byte-by-byte Description of file: table3.dat table4.dat
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Bytes Format Units Label Explanations
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1- 21 A21 --- Name Star identifier in the RAVE catalog or Tycho
23- 26 I4 K Teff Effective temperature of the star
28- 31 F4.2 [cm/s2] logg Surface gravity of the star
33- 37 F5.2 [-] [Fe/H] Metallicity ([Fe/H]) of the star
39- 41 F3.1 km/s vmic Microturbulence velocity
43- 49 F7.4 --- LTE LTE abundance
51- 56 F6.4 --- NLTE NLTE abundance
58 A1 --- flagCMEP [*] * indicates carbon-enhanced metal-poor
stars with s-process element enhancement
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Acknowledgements:
Yanjun Guo, guoyanjun(at)ynao.ac.cn
(End) Patricia Vannier [CDS] 09-Dec-2024