Bibcode
Harutyunyan, G.; Steffen, M.; Mott, A.; Caffau, E.; Israelian, G.; González Hernández, J. I.; Strassmeier, K. G.
Bibliographical reference
Astronomy and Astrophysics, Volume 618, id.A16, 21 pp.
Advertised on:
10
2018
Journal
Citations
23
Refereed citations
18
Description
Context. Convective motions in solar-type stellar atmospheres induce
Doppler shifts that affect the strengths and shapes of spectral
absorption lines and create slightly asymmetric line profiles.
One-dimensional (1D) local thermodynamic equilibrium (LTE) studies of
elemental abundances are not able to reproduce this phenomenon, which
becomes particularly important when modeling the impact of isotopic fine
structure, like the subtle depression created by the 6Li
isotope on the red wing of the Li I resonance doublet line. Aims:
The purpose of this work is to provide corrections for the lithium
abundance, A(Li), and the 6Li/7Li isotopic ratio
that can easily be applied to correct 1D LTE lithium abundances in G and
F dwarf stars of approximately solar mass and metallicity for
three-dimensional (3D) and non-LTE (NLTE) effects. Methods: The
corrections for A(Li) and 6Li/7Li are computed
using grids of 3D NLTE and 1D LTE synthetic lithium line profiles,
generated from 3D hydro-dynamical CO5BOLD and 1D hydrostatic
model atmospheres, respectively. For comparative purposes, all
calculations are performed for three different line lists representing
the Li I λ670.8 nm spectral region. The 3D NLTE corrections are
then approximated by analytical expressions as a function of the stellar
parameters (Teff, log ℊ, [Fe/H], ν sin i, A(Li),
6Li/7Li). These are applied to adjust the 1D LTE
isotopic lithium abundances in two solar-type stars, HD
207129 and HD 95456, for which high-quality
HARPS observations are available. Results: The derived 3D NLTE
corrections range between -0.01 and +0.11 dex for A(Li), and between
-4.9 and -0.4% for 6Li/7Li, depending on the
adopted stellar parameters. We confirm that the inferred 6Li
abundance depends critically on the strength of the Si I 670.8025 nm
line. Our findings show a general consistency with recent works on
lithium abundance corrections. After the application of such
corrections, we do not find a significant amount of 6Li in
any of the two target stars. Conclusions: In the case of
6Li/7Li, our corrections are always negative,
showing that 1D LTE analysis can significantly overestimate the presence
of 6Li (up to 4.9% points) in the atmospheres of solar-like
dwarf stars. These results emphasize the importance of reliable 3D model
atmospheres combined with NLTE line formation for deriving precise
isotopic lithium abundances. Although 3D NLTE spectral synthesis implies
an extensive computational effort, the results can be made accessible
with parametric tools like the ones presented in this work.
The table with the 3D NLTE corrections is only available at the CDS via
anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/618/A16
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