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

Hansen, C. J., El-Souri, M., Monaco, L., Villanova, S., Bonifacio, P., Caffau, E., et al. (2018). Ages and Heavy Element Abundances from Very Metal-poor Stars in the Sagittarius Dwarf Galaxy. The Astrophysical Journal, 855.

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Hansen, Camilla Juul1, Author
El-Souri, Mariam1, Author
Monaco, Lorenzo1, Author
Villanova, Sandro1, Author
Bonifacio, Piercarlo1, Author
Caffau, Elisabetta1, Author
Sbordone, Luca1, Author
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1Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners, ou_2421692              

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Free keywords: galaxies: dwarf galaxies: evolution Galaxy: halo nuclear reactions nucleosynthesis abundances stars: abundances stars: chemically peculiar Astrophysics - Solar and Stellar Astrophysics Astrophysics - Astrophysics of Galaxies
 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] \gtrapprox -1) 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] ̃ -3) 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 9+/- 2.5 {Gyr}. 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 . 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 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 ) 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. Based on data obtained UVES/VLT ID: 083.B-0774, 075.B-0127.

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 Dates: 2018
 Publication Status: Issued
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Title: The Astrophysical Journal
Source Genre: Journal
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Pages: - Volume / Issue: 855 Sequence Number: - Start / End Page: - Identifier: -