A survey for stellar relics of galaxy formation in the large Magellanic cloud

We aim to identify some of the first extremely metal-poor stars in the Large Magellanic Cloud (LMC) based on photometric selection of red giants. The photometric data were from observations using the CTIO 4m Blanco telescope and MOSAIC-II imager, covering 5.4 square degrees of the LMC, extending from the central bar to a projected distance of 8 degrees. Candidates were identifed using Washington photometry, paired with a custom narrowband filter centred on the Calcium II H & K lines - in which metal-poor stars would exhibit greater flux. For the most likely metal-poor candidates, medium resolution spectra were obtained in the visible (R ‚Äöv¢v† 1500), and the infrared (R ‚Äöv¢v† 10000) using the 3.9m AAT telescope with the 2df + AAOmega instruments. The metallicity and radial velocities of these stars were derived from measurements of the near-infrared calcium triplet.

Based on the candidate frequency, the photometric pre-selection proved successful, yielding 104 metal-poor candidates. Of these, 34 stars are previously unknown stars more metal-poor than [Fe/H] = -2:0, with our most metal-poor candidate having a metallicity of [Fe/H] = -2:93. This is the most metal-poor known object in the LMC.

From these results, candidates for high-dispersion follow-up spectroscopy have been identifed.