Using Binary Population Synthesis to Calculate the Yields of Low- and Intermediate-Mass Binary Populations at Low Metallicity

Asymptotic giant branch (AGB) stars are important to chemical evolution at metallicity Z ∼ 0.0001 ([Fe/H] ≈ −2.2) as they contribute significantly to the production of nitrogen, lead, and dust in the early Universe. The contribution of AGB stars to the chemical evolution of the Universe is often quantified using the chemical yields from single AGB stars. Binary evolution challenges our understanding of chemical evolution as binary phenomena such as mergers and mass transfer episodes can significantly alter the stellar evolution pathways and yields. In this work, we use binary population synthesis code BINARY_C to model populations of low and intermediate-mass (∼ 0.7–7 M) stars at metallicity Z = 0.0001. Our binary star populations predict ∼ 37% fewer thermally pulsing AGB stars than our single star populations, leading to a ∼ 40% decrease in the amount of ejected C and a ∼ 35–40% reduction in elements synthesised through the slow neutron capture process. The uncertainty introduced by the mass-loss from stellar winds on the AGB makes the impact of binary evolution on the total amount of ejected N uncertain. The total N yield ejected by our binary star populations ranges from a 17% to a 36% decrease compared to our single star populations. However, our binary populations overproduce N by over an order of magnitude during the period 300–700 Myr after formation.