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arXiv · 1805.11925

The R-Process Alliance: 2MASS J09544277+5246414, the Most Actinide-Enhanced R-II Star Known

Erika M. Holmbeck·Timothy C. Beers·Ian U. Roederer·Vinicius M. Placco·Terese T. Hansen·Charli M. Sakari·Christopher Sneden·Chao Liu·Young Sun Lee·John J. Cowan·Anna Frebel
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Abstract

We report the discovery of a new actinide-boost star, 2MASS J09544277+5246414, originally identified as a very bright (V = 10.1), extremely metal-poor ([Fe/H] = -2.99) K giant in the LAMOST survey, and found to be highly r-process-enhanced (r-II; [Eu/Fe]= +1.28]), during the snapshot phase of the R-Process Alliance (RPA). Based on a high S/N, high-resolution spectrum obtained with the Harlan J. Smith 2.7-m telescope, this star is the first confirmed actinide-boost star found by RPA efforts. With an enhancement of [Th/Eu] = +0.37, 2MASS J09544277+5246414 is also the most actinide-enhanced r-II star yet discovered, and only the sixth metal-poor star with a measured uranium abundance ([U/Fe] = +1.40). Using the Th/U chronometer, we estimate an age of 13.0+/-4.7 Gyr for this star. The unambiguous actinide-boost signature of this extremely metal-poor star, combined with additional r-process-enhanced and actinide-boost stars identified by the RPA, will provide strong constraints on the nature and origin of the r-process at early times.

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Erika M. Holmbeck, Timothy C. Beers, Ian U. Roederer, Vinicius M. Placco, Terese T. Hansen, Charli M. Sakari, Christopher Sneden, Chao Liu, Young Sun Lee, John J. Cowan, Anna Frebel. 2018-05-30. The R-Process Alliance: 2MASS J09544277+5246414, the Most Actinide-Enhanced R-II Star Known. https://doi.org/10.3847/2041-8213%2Faac722

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