High-resolution spectroscopic study of extremely metal-poor stars in the Large Magellanic Cloud

TL;DR

This study analyzes the chemical compositions of the most metal-poor stars in the Large Magellanic Cloud using high-resolution spectroscopy, revealing similarities with Milky Way halo stars and insights into early galaxy enrichment processes.

Contribution

First detailed high-resolution abundance analysis of extremely metal-poor stars in the LMC, providing new insights into early chemical enrichment and r-process element distribution.

Findings

Confirmed the discovery of the most metal-poor stars in the LMC.

Found that some stars are enhanced in r-process elements, contrasting previous literature.

Suggested a minimum delay time of ~100 Myr for neutron star mergers to produce r-process elements in the LMC.

Abstract

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] $\leq$ --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 $\sim$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.