The SkyMapper search for extremely metal-poor stars in the Large Magellanic Cloud

TL;DR

This study identifies the most metal-poor stars in the Large Magellanic Cloud using SkyMapper photometry, Gaia data, and spectroscopic analysis, providing insights into early star formation in dwarf galaxies.

Contribution

It introduces a novel method combining photometry, Gaia data, and spectroscopy to find extremely metal-poor stars in the LMC, discovering the most metal-poor stars in this galaxy to date.

Findings

Seven stars with [Fe/H] ≤ -2.75 identified

Two stars with [Fe/H] ≤ -3 discovered

Confirmed LMC membership through phase-space analysis

Abstract

We present results of a search for extremely metal-poor (EMP) stars in the Large Magellanic Cloud, which can provide crucial information about the properties of the first stars as well as on the formation conditions prevalent during the earliest stages of star formation in dwarf galaxies. Our search utilised SkyMapper photometry, together with parallax and proper motion cuts (from Gaia), colour-magnitude cuts (by selecting the red giant branch region) and finally a metallicity-sensitive cut. Low-resolution spectra of a sample of photometric candidates were taken using the ANU 2.3m telescope/WiFeS spectrograph, from which 7 stars with [Fe/H] $\leq$ -2.75 were identified, two of which have [Fe/H] $\leq$ -3. Radial velocities, derived from the CaII triplet lines, closely match the outer rotation curve of the LMC for the majority of the candidates in our sample. Therefore, our targets are robustly members of the LMC based on their 6D phase-space information (coordinates, spectrophotometric distance, proper motions and radial velocities), and they constitute the most metal-poor stars so far discovered in this galaxy.