The most metal-poor stars provide a direct observational window into the earliest phases of star formation and chemical enrichment in the Universe. These objects, formed from gas enriched by only one or a few nucleosynthetic events, preserve the chemical fingerprints of the first generations of stars. In this talk, I will present our ongoing effort to identify and characterise such “chemical outliers” using large spectroscopic surveys, including DESI, combined with targeted follow-up observations.
I will discuss recent discoveries of ultra metal-poor stars, including objects at [Fe/H] < −5, and highlight their diverse abundance patterns, which challenge standard enrichment scenarios. Particular attention will be given to carbon-enhanced metal-poor stars and their implications for early nucleosynthesis, as well as to the role of these stars in constraining Population III supernova yields.
Finally, I will outline how the rapidly growing sample of extremely metal-poor stars enables a statistical approach to Galactic archaeology, providing new constraints on the formation of the Milky Way halo and the nature of the first stellar populations.
