J/A+A/585/A102 Copper abundances in solar neighborhood stars (Yan+, 2016)
Non-LTE analysis of copper abundances for the two distinct halo populations in
the solar neighborhood.
Yan H.L., Shi J.R., Nissen P.E., Zhao G.
<Astron. Astrophys., 585, A102-102 (2016)>
=2016A&A...585A.102Y 2016A&A...585A.102Y (SIMBAD/NED BibCode)
ADC_Keywords: Stars, nearby ; Abundances
Keywords: Galaxy: evolution - Galaxy: halo - line: formation - line: profiles -
stars: abundances - stars: atmospheres
Abstract:
Two distinct halo populations were found in the solar neighborhood by
a series of works. They can be clearly separated by [α/Fe] and
several other elemental abundance ratios including [Cu/Fe]. Very
recently, a non-local thermodynamic equilibrium (non-LTE) study
revealed that relatively large departures exist between LTE and
non-LTE results in copper abundance analysis. The study also showed
that non-LTE effects of neutral copper vary with stellar parameters
and thus affect the [Cu/Fe] trend. We aim to derive the copper
abundances for the stars from the sample of Nissen & Schuster
(2010A&A...511L..10N 2010A&A...511L..10N) with both LTE and non-LTE calculations. Based on
our results, we study the non-LTE effects of copper and investigate
whether the high-α population can still be distinguished from
the low-α population in the non-LTE [Cu/Fe] results. Our
differential abundance ratios are derived from the high-resolution
spectra collected from VLT/UVES and NOT/FIES spectrographs. Applying
the MAFAGS opacity sampling atmospheric models and spectrum synthesis
method, we derive the non-LTE copper abundances based on the new
atomic model with current atomic data obtained from both laboratory
and theoretical calculations. The copper abundances determined from
non-LTE calculations are increased by 0.01 to 0.2dex depending on the
stellar parameters compared with the LTE results. The non-LTE [Cu/Fe]
trend is much flatter than the LTE one in the metallicity range
-1.6<[Fe/H]←0.8. Taking non-LTE effects into consideration, the high-
and low-α stars still show distinguishable copper abundances,
which appear even more clear in a diagram of non-LTE [Cu/Fe] versus
[Fe/H]. The non-LTE effects are strong for copper, especially in
metal-poor stars. Our results confirmed that there are two distinct
halo populations in the solar neighborhood. The dichotomy in copper
abundance is a peculiar feature of each population, suggesting that
they formed in different environments and evolved obeying diverse
scenarios.
Description:
We investigated 94 dwarfs with effective temperatures between 5200K
and 6300K and a metallicity range from -1.6 to -0.4, of which 78
belong to the halo population and the remaining 16 are from the thick
disk. The stars were observed using either the ESO/VLT UVES
spectrograph (with a resolution R∼55000 and a signal-to-noise ratio
S/N∼250-500) or the NOT/FIES spectrograph (R∼40000, S/N∼140-200).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 109 47 LTE and non-LTE copper abundance ratios [Cu/Fe]
for stars with VLT/UVES spectra
tablea2.dat 108 36 *LTE and non-LTE copper abundance ratios [Cu/Fe]
for stars with NOT/FIES spectra
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Note on tablea2.dat: The stars without available copper abundance are not
listed in the table.
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Byte-by-byte Description of file: tablea?.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Star Star name
12 A1 --- n_Star [a] a for stars having NOT/FIES and
VLT/UVES spectra
14- 17 I4 K Teff ?=- Effective temperature
19- 22 F4.2 [cm/s2] logg ?=- Surface gravity
24- 28 F5.2 [-] [Fe/H] ?=- Metallicity
30- 33 F4.2 km/s vt ?=- Microturbulent velocity
35- 38 F4.2 [-] [a/Fe] ?=- [alpha/Fe] abundance (2)
40- 44 F5.2 [-] 5105AL LTE Abundance ratios derived from
CuI 5105Å line
46- 50 F5.2 [-] 5218AL ?=- LTE Abundance ratios derived from
CuI 5218Å line
52- 56 F5.2 --- 5782AL ?=- LTE Abundance ratios derived from
CuI 5782Å line
58- 62 F5.2 [-] [Cu/Fe]L LTE Abunbance [Cu/Fe]
64- 67 F4.2 [-] e_[Cu/Fe]L rms uncertainty on [Cu/Fe]L
69- 73 F5.2 [-] 5105AN Non-LTE Abundance ratios derived from
CuI 5105Å line
75- 79 F5.2 [-] 5218AN ?=- Non-LTE Abundance ratios derived from
CuI 5218Å line
81- 85 F5.2 --- 5782AN ?=- Non-LTE Abundance ratios derived from
CuI 5782Å line
87- 91 F5.2 [-] [Cu/Fe]N Non-LTE Abunbance [Cu/Fe]
93- 96 F4.2 [-] e_[Cu/Fe]N rms uncertainty on [Cu/Fe]N
98-109 A12 --- Class Classification (1)
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Note (1): The classification is indicated by "TD" (thick-disk),
"high-alpha" and "low-alpha",
and a "?" are added if the classification is uncertain.
Note (2): The stellar parameters including [alpha/Fe] are the same as
Nissen & Schuster (2010, Cat. J/A+A/511/L10).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 10-Mar-2016