J/A+A/554/A96 Spectra of LiI(670.8nm) line in metal-poor stars (Lind+, 2013)
The lithium isotopic ratio in very metal-poor stars.
Lind K., Melendez J., Asplund M., Collet R., Magic Z.
<Astron. Astrophys. 554, A96 (2013)>
=2013A&A...554A..96L 2013A&A...554A..96L
ADC_Keywords: Spectroscopy ; Stars, metal-deficient ; Abundances
Keywords: stars: abundances - stars: Population II -
primordial nucleosynthesis - techniques: spectroscopic -
line: profiles - line: formation
Abstract:
Un-evolved, very metal-poor stars are the most important tracers of
the cosmic abundance of lithium in the early universe. Combining the
standard Big Bang nucleosynthesis model with Galactic production
through cosmic ray spallation, these stars at [Fe/H]←2 are expected
to show an undetectably small 6Li/7Li isotopic signature. Evidence
to the contrary may necessitate an additional pre-galactic production
source or a revision of the standard model of Big Bang
nucleosynthesis. It would also cast doubts on Li depletion from
stellar atmospheres as an explanation for the factor 3-5 discrepancy
between the predicted primordial 7Li from the Big Bang and the
observed value in metal-poor dwarf/turn-off stars.
We revisit the isotopic analysis of four halo stars, two with claimed
6Li-detections in the literature, to investigate the influence of
improved model atmospheres and line formation treatment.
For the first time, a combined 3D, non-local thermodynamic equilibrium
(NLTE) modelling technique for Li, Na, and Ca lines is utilised to
constrain the intrinsic line-broadening and to determine the Li
isotopic ratio. We discuss the influence of 3D NLTE effects on line
profile shapes and assess the realism of our modelling using the Ca
excitation and ionisation balance.
By accounting for NLTE line formation in realistic 3D hydrodynamical
model atmospheres, we can model the Li resonance line and other
neutral lines with a consistency that is superior to LTE, with no need
for additional line asymmetry caused by the presence of 6Li. Contrary
to the results from 1D and 3D LTE modelling, no star in our sample has
a significant (2 sigma) detection of the lighter isotope in NLTE. Over
a large parameter space, NLTE modelling systematically reduces the
best-fit Li isotopic ratios by up to five percentage points. As a
bi-product, we also present the first ever 3D NLTE Ca and Na
abundances of halo stars, which reveal significant departures from
LTE.
The observational support for a significant and non-standard 6Li
production source in the early universe is substantially weakened by
our findings.
Description:
Reduced spectra in the region around the LiI 670.8nm resonance line.
Four stars have been observed: HD19445, HD84937, HD140283 and G64-12.
For each star, wavelength and normalised flux are given. For the
derivation of the Li isotopic ratio, the normalisation has been
further fine-tuned in a spectral interval extending 0.17nm from the
line centre.
Objects:
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RA (2000) DE Designation(s)
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03 08 25.59 +26 19 51.4 HD 19445 = HIP 14594
09 48 56.10 +13 44 39.3 HD 84937 = HIP 48152
15 43 03.10 -10 56 00.6 HD 140283 = HIP 76976
13 40 02.50 -00 02 18.8 G64-12 = HIP 66673
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
g64-12.dat 27 923 G64-12 wavelength and normalised flux
hd140283.dat 27 853 HD 140283 wavelength and normalised flux
hd19445.dat 27 921 HD 19445 wavelength and normalised flux
hd84937.dat 27 921 HD 84937 wavelength and normalised flux
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Byte-by-byte Description of file: *.dat
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Bytes Format Units Label Explanations
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1- 16 F16.12 nm lambda [669.9/672.6] Wavelength λ
19- 27 F9.7 --- Flux Normalised flux
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Acknowledgements:
Jorge Melendez, jorge(at)astro.iag.usp.br
(End) Karin Lind [IoA, Cambridge, UK], Patricia Vannier [CDS] 11-Jun-2013