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A New Test of Copper and Zinc Abundances in Late-type Stars Using Ultraviolet Cu II and Zn II Lines
Univ Michigan, Dept Astron, 1085 S Univ Ave, Ann Arbor, MI 48109 USA.;JINA CEE, E Lansing, MI 48824 USA..
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
2018 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 857, no 1, article id 2Article in journal (Refereed) Published
Abstract [en]

We present new abundances derived from Cu I, Cu II, Zn I, and Zn II lines in six warm (5766 <= T-eff <= 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 (less than or similar to 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.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD , 2018. Vol. 857, no 1, article id 2
Keywords [en]
nuclear reactions, nucleosynthesis, abundances, stars: abundances, stars: atmospheres, stars: individual, stars: population II, ultraviolet: stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-352482DOI: 10.3847/1538-4357/aab71fISI: 000429348600002OAI: oai:DiVA.org:uu-352482DiVA, id: diva2:1215362
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationAvailable from: 2018-06-08 Created: 2018-06-08 Last updated: 2018-12-11

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