Nucleosynthesis in a primordial supernova: Carbon and oxygen abundances in SMSS J031300.36–670839.3

SMSS J031300.36–670839.3 (hereafter SM0313–6708) is a sub-giant halo star, with no detectable Fe lines and large overabundances of C and Mg relative to Ca. We obtained Very Large Telescope–Ultraviolet and Visual Echelle Spectrograph (UVES) spectra extending to 3060 Å showing strong OH A-X band lines enabling an oxygen abundance to be derived. The OH A-X band lines in SM0313–6708 are much stronger than the CH C-X band lines. Spectrum synthesis fits indicate an [$O/C$] ratio of 0.02 ± 0.175. Our high signal-to-noise ratio UVES data also enabled us to lower the Fe abundance limit to ${\left[Fe/H\right]}_{⟨3D⟩,NLTE}<-7.52$ (3σ). These data support our previous suggestion that the star formed from the iron-poor ejecta of a single massive star Population III supernova.