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The Hamburg/ESO R-process Enhanced Star survey (HERES): VII. Thorium abundances in metal-poor stars
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
2012 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 537, A118Article in journal (Refereed) Published
Abstract [en]

We report thorium abundances for 77 metal-poor stars in the metallicity range of -3.5 < [Fe/H] < -1.0, based on "snapshot" spectra obtained with VLT-UT2/UVES during the HERES Survey. We were able to determine the thorium abundances with better than 1 sigma confidence for 17 stars, while for 60 stars we derived upper limits. For five stars common with previous studies, our results were in good agreement with the literature results. The thorium abundances span a wide range of about 4.0 dex, and scatter exists in the distribution of log (Th/Eu) ratios for lower metallicity stars, supporting previous studies suggesting the r-process is not universal. We derived ages from the log (Th/Eu) ratios for 12 stars, resulting in large scattered ages, and two stars with significant enhancement of Th relative to Eu are found, indicating the "actinide boost" does not seem to be a rare phenomenon and thus highlighting the risk in using log (Th/Eu) to derive stellar ages.

Place, publisher, year, edition, pages
2012. Vol. 537, A118
Keyword [en]
stars: evolution, stars: abundances, galaxies: evolution, Galaxy: halo, stars: Population II, Galaxy: abundances
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-247774DOI: 10.1051/0004-6361/201118241ISI: 000300416800118OAI: oai:DiVA.org:uu-247774DiVA: diva2:797401
Available from: 2015-03-23 Created: 2015-03-23 Last updated: 2017-12-04Bibliographically approved

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