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

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. BertinD. 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. Thomas, D. L. Tucker, A. R. Walker, R. H. Wechsler, R. C. Wolf, B. Yanny

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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


  • astro-ph.SR
  • astro-ph.GA
  • RCUK
  • STFC
  • AST-1560223


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