Pristine Inner Galaxy Survey (PIGS) IX. The largest detailed chemical analysis of very metal-poor stars in the Sagittarius dwarf galaxy
arxiv(2024)
摘要
The most metal-poor stars provide valuable insights into the early chemical
enrichment history of a system, carrying the chemical imprints of the first
generations of supernovae. The most metal-poor region of the Sagittarius dwarf
galaxy remains inadequately observed and characterised. To date, only a handful
of stars with [Fe/H]<-2.0 have been chemically analysed with high-resolution
spectroscopy. In this study, we present the most extensive chemical abundance
analysis of 12 low-metallicity stars with metallicities down to [Fe/H]=-3.26
and located in the main body of Sagittarius. These targets, selected from the
Pristine Inner Galaxy survey, were observed using the MIKE high-resolution
spectrograph at the Magellan-Clay telescope, which allows us to measure up to
17 chemical species. The chemical composition of these stars reflects the
imprint of a variety of type II supernovae. A combination of low- to
intermediate-mass core-collapse and hypernovae (∼10-70 M_⊙) is
required to account for the abundance patterns of the lighter elements up to
the Fe-peak. The trend of the heavy elements suggests the involvement of
compact binary merger events and fast-rotating (up to ∼300 km s^-1)
intermediate-mass to massive metal-poor stars (∼25-120 M_⊙) that are
the sources of rapid- and slow-processes, respectively. Additionally,
asymptotic giant branch stars contribute to a wide dispersion of [Ba/Mg] and
[Ba/Eu]. The absence of an α-knee in our data indicates that type Ia
supernovae did not contribute in the very metal-poor region (
[Fe/H]≤-2.0). However, they might have started to pollute the interstellar
medium at [Fe/H]>-2.0, given the relatively low [Co/Fe] in this metallicity
region.
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