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A New Test of Copper and Zinc Abundances in Late-type Stars Using Ultraviolet Cu ii and Zn ii Lines
We present new abundances derived from Cu i , Cu ii , Zn i , and Zn ii lines in six warm (5766 ≤ ≤ 6427 K), metal-poor (−2.50 ≤ [Fe/H] ≤ −0.95) dwarf and subgiant (3.64 ≤ log g ≤ 4.44) stars. These abundances are derived from archival high-resolution ultraviolet spectra from the Space Telescope Ima...
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Published in: | The Astrophysical journal 2018-04, Vol.857 (1), p.2 |
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Main Authors: | , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | We present new abundances derived from Cu
i
, Cu
ii
, Zn
i
, and Zn
ii
lines in six warm (5766 ≤
≤ 6427 K), metal-poor (−2.50 ≤ [Fe/H] ≤ −0.95) dwarf and subgiant (3.64 ≤ log
g
≤ 4.44) stars. These abundances are derived from archival high-resolution ultraviolet spectra from the Space Telescope Imaging Spectrograph on board the
Hubble Space Telescope
and ground-based optical spectra from several observatories. Ionized Cu and Zn are the majority species, and abundances derived from Cu
ii
and Zn
ii
lines should be largely insensitive to departures from local thermodynamic equilibrium (LTE). We find good agreement between the [Zn/H] ratios derived separately from Zn
i
and Zn
ii
lines, suggesting that departures from LTE are, at most, minimal (≲0.1 dex). We find that the [Cu/H] ratios derived from Cu
ii
lines are 0.36 ± 0.06 dex larger than those derived from Cu
i
lines in the most metal-poor stars ([Fe/H] < −1.8), suggesting that LTE underestimates the Cu abundance derived from Cu
i
lines. The deviations decrease in more metal-rich stars. Our results validate previous theoretical non-LTE calculations for both Cu and Zn, supporting earlier conclusions that the enhancement of [Zn/Fe] in metal-poor stars is legitimate, and the deficiency of [Cu/Fe] in metal-poor stars may not be as large as previously thought. |
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ISSN: | 0004-637X 1538-4357 1538-4357 |
DOI: | 10.3847/1538-4357/aab71f |