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The R-Process alliance: Discovery of a Low-α, r-process-enhanced Metal-poor Star in the Galactic Halo

Sakari, Charli M.; Roederer, Ian U.; Placco, Vinicius M.; Beers, Timothy C.; Ezzeddine, Rana; Frebel, Anna; Hansen, Terese; Sneden, Christopher; Cowan, John J.; Wallerstein, George; Farrell, Elizabeth M.; Venn, Kim A.; Matijevič, Gal; Wyse, Rosemary F. G.; Bland-Hawthorn, Joss; Chiappini, Cristina; Freeman, Kenneth C.; Gibson, Brad K.; Grebel, Eva K.; Helmi, Amina; Kordopatis, Georges; Kunder, Andrea; Navarro, Julio; Reid, Warren; Seabroke, George; Steinmetz, Matthias; Watson, Fred

Abstract

A new moderately r-process-enhanced metal-poor star, RAVE J093730.5−062655, has been identified in the Milky Way halo as part of an ongoing survey by the R-Process Alliance. The temperature and surface gravity indicate that J0937−0626 is likely a horizontal branch star. At [Fe/H] = −1.86, J0937−0626 is found to have subsolar [X/Fe] ratios for nearly every light, α, and Fe-peak element. The low [α/Fe] ratios can be explained by an ~0.6 dex excess of Fe; J0937−0626 is therefore similar to the subclass of "iron-enhanced" metal-poor stars. A comparison with Milky Way field stars at [Fe/H] = −2.5 suggests that J0937−0626 was enriched in material from an event, possibly a Type Ia supernova, that created a significant amount of Cr, Mn, Fe, and Ni and smaller amounts of Ca, Sc, Ti, and Zn. The r-process enhancement of J0937−0626 is likely due to a separate event, which suggests that its birth environment was highly enriched in r-process elements. The kinematics of J0937−0626, based on Gaia DR2 data, indicate a retrograde orbit in the Milky Way halo; J0937−0626 was therefore likely accreted from a dwarf galaxy that had significant r-process enrichment.

Journal Article Type Article
Publication Date Apr 2, 2019
Journal The Astrophysical Journal
Print ISSN 0004-637X
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 874
Issue 2
Pages 148
DOI https://doi.org/10.3847/1538-4357/ab0c02
Keywords Space and Planetary Science; Astronomy and Astrophysics
Publisher URL https://iopscience.iop.org/article/10.3847/1538-4357/ab0c02/meta
Additional Information Journal title: The Astrophysical Journal; Article type: paper; Article title: The R-Process Alliance: Discovery of a Low-α, r-process-enhanced Metal-poor Star in the Galactic Halo; Copyright information: © 2019. The American Astronomical Society. All rights reserved.; Date received: 2018-11-15; Date accepted: 2019-03-01; Online publication date: 2019-04-02

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Copyright Statement
© 2019. The American Astronomical Society. All rights reserved.



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