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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

Authors

Charli M. Sakari

Ian U. Roederer

Vinicius M. Placco

Timothy C. Beers

Rana Ezzeddine

Anna Frebel

Terese Hansen

Christopher Sneden

John J. Cowan

George Wallerstein

Elizabeth M. Farrell

Kim A. Venn

Gal Matijevič

Rosemary F. G. Wyse

Joss Bland-Hawthorn

Cristina Chiappini

Kenneth C. Freeman

Eva K. Grebel

Amina Helmi

Georges Kordopatis

Andrea Kunder

Julio Navarro

Warren Reid

George Seabroke

Matthias Steinmetz

Fred Watson

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
Institution Citation Sakari, C. M., Roederer, I. U., Placco, V. M., Beers, T. C., Ezzeddine, R., Frebel, A., …Watson, F. (2019). The R-Process alliance: Discovery of a Low-α, r-process-enhanced Metal-poor Star in the Galactic Halo. The Astrophysical journal, 874(2), 148. https://doi.org/10.3847/1538-4357/ab0c02
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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