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The R-process alliance: discovery of the first metal-poor star with a combined r- and s-process element signature

Author(s)
Gull, Maude; Frebel, Anna; Cain, Madelyn G.; Ji, Alexander P.; Ezzeddine, Rana
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Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
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Abstract
We present a high-resolution (R ∼ 35,000), high signal-to-noise ratio (S/N > 200) Magellan/MIKE spectrum of the star RAVE J094921.8-161722, a bright (V = 11.3) metal-poor red giant star with [Fe/H] = -2.2, identified as a carbon-enhanced metal-poor (CEMP) star from the RAVE survey. We report its detailed chemical abundance signature of light fusion elements and heavy neutron-capture elements. We find J0949-1617 to be a CEMP star with s-process enhancement that must have formed from gas enriched by a prior r-process event. Light neutron-capture elements follow a low-metallicity s-process pattern, while the heavier neutron-capture elements above Eu follow an r-process pattern. The Pb abundance is high, in line with an s-process origin. Thorium is also detected, as expected from an r-process origin, as Th is not produced in the s-process. We employ nucleosynthesis model predictions that take an initial r-process enhancement into account, and then determine the mass transfer of carbon and s-process material from a putative more massive companion onto the observed star. The resulting abundances agree well with the observed pattern. We conclude that J0949-1617 is the first bonafide CEMP-r + s star identified. This class of objects has previously been suggested to explain stars with neutron-capture element patterns that originate from neither the r- nor the s-process alone. We speculate that J0949-1617 formed in an environment similar to those of ultra-faint dwarf galaxies like Tucana III and Reticulum II, which were enriched in r-process elements by one or multiple neutron star mergers at the earliest times. ©2018
Date issued
2018-08
URI
https://hdl.handle.net/1721.1/124503
Department
MIT Kavli Institute for Astrophysics and Space Research
Journal
Astrophysical journal
Publisher
American Astronomical Society
Citation
Gull, Maude, et al., "The R-process alliance: discovery of the first metal-poor star with a combined r- and s-process element signature." Astrophysical journal 862, 2 (2018): p. 174- doi 10.3847/1538-4357/AACBC3 ©2018 Author(s)
Version: Final published version
ISSN
1538-4357

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