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Detection of Pb II in the Ultraviolet Spectra of Three Metal-poor Stars
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Roederer_2020_ApJL_902_L24.pdf
Description
Published version
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469.46 KB
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Adobe PDF
Checksum (MD5)
f31e2d5a116e9bd5e9c315cda7146dde
Author(s)
Roederer, Ian U
Lawler, James E
Holmbeck, Erika M
Beers, Timothy C
Ezzeddine, Rana
Frebel, Anna
Hansen, Terese T
Ivans, Inese I
Karakas, Amanda I
Placco, Vinicius M
Date Issued
2020
Journal
Astrophysical Journal Letters
Publisher
American Astronomical Society
Citation
Roederer, Ian U, Lawler, James E, Holmbeck, Erika M, Beers, Timothy C, Ezzeddine, Rana et al. 2020. "Detection of Pb II in the Ultraviolet Spectra of Three Metal-poor Stars." Astrophysical Journal Letters, 902 (1).
Version
Final published version
Abstract
© 2020. The American Astronomical Society. All rights reserved.. We report the first detection of the Pb ii line at 2203.534 Å in three metal-poor stars, using ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We perform a standard abundance analysis assuming local thermodynamic equilibrium (LTE) to derive lead (Pb, Z = 82) abundances. The Pb ii line yields a higher abundance than Pb i lines by +0.36 ± 0.34 dex and +0.49 ± 0.28 dex in the stars HD 94028 and HD 196944, where Pb i lines had been detected previously. The Pb ii line is likely formed in LTE, and these offsets affirm previous calculations showing that Pb i lines commonly used as abundance indicators underestimate the Pb abundance in LTE. Pb is enhanced in the s-process-enriched stars HD 94028 ([Pb/Fe] = +0.95 ± 0.14) and HD 196944 ([Pb/Fe] = +2.28 ± 0.23), and we show that 208Pb is the dominant Pb isotope in these two stars. The log (Pb/Eu) ratio in the r-process-enhanced star HD 222925 is 0.76 ± 0.14, which matches the solar system r-process ratio and indicates that the solar system r-process residuals for Pb are, in aggregate, correct. The Th/Pb chronometer in HD 222925 yields an age of 8.2 ± 5.8 Gyr, and we highlight the potential of the Th/Pb chronometer as a relatively model-insensitive age indicator in r-process-enhanced stars.
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DOI of Published Version
10.3847/2041-8213/ABBC21
