Program: GN-2022B-Q-211

Within the standard cold dark matter paradigm, the first (Pop. III) stars were the main drivers of early cosmic evolution. Hence, through the mass spectrum of the first stars, we can empirically determine the physical conditions that existed in the environments in which these objects were born at high redshift (z ~ 20). To achieve this, we need to compare the chemical compositions of genuine "second-generation" stars with yields of metal-free supernovae to find the masses of their progenitors. Unfortunately, extremely metal-poor (EMP, [Fe/H] < -2.5) stars, those with reasonable (between 20% and 50%) probability of being enriched by a single supernova, are exceedingly rare. We propose high-resolution (R = 40,000) spectroscopic follow-up of 16 exquisitely bright (11.4 < V < 13.6) previously identified EMP stars with GRACES at Gemini North. These observations will be utilized to measure a large set of elemental abundances for these stars which will, then, be compared to Pop. III supernovae models in a statistical framework. This exercise will allow us to derive the masses of previous (first) generations of stars and the explosion energies of their associated supernovae events to be contrasted with predictions from corcordance cosmology.