Beryllium abundances and the early Galactic chemical enrichment

Beryllium is a light element with a single stable isotope, 9Be, which can only be produced by cosmic-ray spallation in the interstellar medium. Its unique nucleosynthesis offers a different point of view from which one can investigate the early Galactic chemical enrichment. Our previous results have shown that there is a large scatter when Be abundances are plotted as a function of metallicity ([Fe/H]) in a sample extremely metal-poor stars ([Fe/H] < -3.0). Using Gaia DR2 data, we were able to show that this scatter was connected to a mixed origin of the halo stars (some were accreted stars and some formed in situ). Our interpretation is that Fe, and not Be, dominates the scatter as a consequence of the inhomogeneous star forming conditions in the early Galaxy. Without efficient mixing, the early interstellar medium would be characterised by a large scatter in Fe abundances at a given age. Beryllium, on the other hand, because of its origins in cosmic-ray spallation, would have more homogeneous abundances (in a Galaxy-wide sense). In this contribution, we revisit the results using Gaia DR3 data to investigate the kinematic and dynamical properties of the stars. In addition, we estimate ages for the sample and, using literature data, extend the investigation of the Be and Fe scatter, as a function of stellar dynamics, to metallicities up to [Fe/H] ~ -2.0.R.S. acknowledges support by the National Science Centre, Poland, through project 2018/31/B/ST9/01469