Ages and Heavy Element Abundances from Very Metal-poor Stars in the Sagittarius Dwarf Galaxy

Camilla Juul Hansen, Mariam El-Souri, Lorenzo Monaco, Sandro Villanova, Piercarlo Bonifacio, Elisabetta Caffau, Luca Sbordone

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)

Abstract

Sagittarius (Sgr) is a massive disrupted dwarf spheroidal galaxy in the Milky Way halo that has undergone several stripping events. Previous chemical studies were restricted mainly to a few, metal-rich ([Fe/H] ) stars that suggested a top-light initial mass function (IMF). Here we present the first high-resolution, very metal-poor ([Fe/H] =-1 to -3) sample of 13 giant stars in the main body of Sgr. We derive abundances of 13 elements, namely C, Ca, Co, Fe, Sr, Ba, La, Ce, Nd, Eu, Dy, Pb, and Th, that challenge the interpretation based on previous studies. Our abundances from Sgr mimic those of the metal-poor halo, and our most metal-poor star ([Fe/H] ) indicates a pure r-process pollution. Abundances of Sr, Pb, and Th are presented for the first time in Sgr, allowing for age determination using nuclear cosmochronology. We calculate ages of . Most of the sample stars have been enriched by a range of asymptotic giant branch (AGB) stars with masses between 1.3 and 5 M o. Sgr J190651.47-320147.23 shows a large overabundance of Pb (2.05 dex) and a peculiar abundance pattern best fit by a 3 M o AGB star. Based on star-to-star scatter and observed abundance patterns, a mixture of low- and high-mass AGB stars and supernovae (15-25 M o) is necessary to explain these patterns. The high level (0.29 0.05 dex) of Ca indicates that massive supernovae must have existed and polluted the early ISM of Sgr before it lost its gas. This result is in contrast with a top-light IMF with no massive stars polluting Sgr.

Original languageEnglish
Article number83
JournalAstrophysical Journal
Volume855
Issue number2
DOIs
Publication statusPublished - 10 Mar 2018

Keywords

  • galaxies: dwarf
  • galaxies: evolution
  • Galaxy: halo
  • nuclear reactions, nucleosynthesis, abundances
  • stars: abundances
  • stars: chemically peculiar

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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