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Chemical abundance analysis of three α-poor, metal-poor stars in the ultrafaint dwarf galaxy Horologium I

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  • D. Q. Nagasawa
  • J. L. Marshall
  • J. D. Simon
  • T. T. Hansen
  • T. S. Li
  • R. A. Bernstein
  • E. Balbinot
  • A. Drlica-Wagner
  • A. B. Pace
  • L. E. Strigari
  • C. M. Pellegrino
  • D. L. DePoy
  • N. B. Suntzeff
  • K. Bechtol
  • T. M. C. Abbott
  • F. B. Abdalla
  • S. Allam
  • J. Annis
  • A. Benoit-Lévy
  • E. Bertin
  • D. Brooks
  • A. Carnero Rosell
  • M. Carrasco Kind
  • J. Carretero
  • C. E. Cunha
  • C. B. D'Andrea
  • L. N. da Costa
  • C. Davis
  • S. Desai
  • P. Doel
  • T. F. Eifler
  • B. Flaugher
  • P. Fosalba
  • J. Frieman
  • J. García-Bellido
  • E. Gaztanaga
  • D. W. Gerdes
  • D. Gruen
  • R. A. Gruendl
  • J. Gschwend
  • G. Gutierrez
  • W. G. Hartley
  • K. Honscheid
  • D. J. James
  • T. Jeltema
  • E. Krause
  • K. Kuehn
  • S. Kuhlmann
  • N. Kuropatkin
  • M. March
  • R. Miquel
  • B. Nord
  • A. Roodman
  • E. Sanchez
  • B. Santiago
  • V. Scarpine
  • R. Schindler
  • M. Schubnell
  • I. Sevilla-Noarbe
  • M. Smith
  • R. C. Smith
  • M. Soares-Santos
  • F. Sobreira
  • E. Suchyta
  • G. Tarle
  • D. L. Tucker
  • A. R. Walker
  • R. H. Wechsler
  • R. C. Wolf
  • B. Yanny
We present chemical abundance measurements of three stars in the ultrafaint dwarf galaxy Horologium I, a Milky Way satellite discovered by the Dark Energy Survey. Using high-resolution spectroscopic observations, we measure the metallicity of the three stars, as well as abundance ratios of several α-elements, iron-peak elements, and neutron-capture elements. The abundance pattern is relatively consistent among all three stars, which have a low average metallicity of [Fe/H] ~ −2.6 and are not α-enhanced ([α/Fe] ~ 0.0). This result is unexpected when compared to other low-metallicity stars in the Galactic halo and other ultrafaint dwarfs and suggests the possibility of a different mechanism for the enrichment of Hor I compared to other satellites. We discuss possible scenarios that could lead to this observed nucleosynthetic signature, including extended star formation, enrichment by a Population III supernova, and or an association with the Large Magellanic Cloud.
Original languageEnglish
Article number99
Number of pages16
JournalThe Astrophysical Journal
Issue number2
Publication statusPublished - 11 Jan 2018


  • Nagasawa_2018_ApJ_852_99

    Rights statement: D. Q. Nagasawa et al 2018 ApJ 852 99. Reproduced by permission of the AAS.

    Final published version, 2.59 MB, PDF document

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