High-resolution spectroscopic study of extremely metal-poor stars in the Large Magellanic Cloud
arxiv(2023)
摘要
We present detailed abundance results based on UVES high dispersion spectra
for 7 very and extremely metal-poor stars in the Large Magellanic Cloud. We
confirm that all 7 stars, two of which have [Fe/H] ≤ –3.0, are the most
metal-poor stars discovered so far in the Magellanic Clouds. The element
abundance ratios are generally consistent with Milky Way halo stars of similar
[Fe/H] values. We find that 2 of the more metal-rich stars in our sample are
enhanced in r-process elements. This result contrasts with the literature,
where all nine metal-poor LMC stars with higher [Fe/H] values than our sample
were found to be rich in r-process elements. The absence of r-process
enrichment in stars with lower [Fe/H] values is consistent with a minimum delay
timescale of ∼100 Myr for the neutron star binary merger process to
generate substantial r-process enhancements in the LMC. We find that the
occurrence rate of r-process enhancement (r-I or r-II) in our sample of very
and extremely metal-poor stars is statistically indistinguishable from that
found in the Milky Way's halo, although including stars from the literature
sample hints at a larger r-II frequency the LMC. Overall, our results shed
light on the earliest epochs of star formation in the LMC that may be
applicable to other galaxies of LMC-like mass.
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