Probing the Lithium Plateau: Radial Velocity Monitoring of Rare Very Metal-Poor Binaries

The "Spite Plateau" of Lithium abundance remains a critical test for Big Bang Nucleosynthesis and stellar evolution. We present a study of very metal-poor (VMP) double-lined spectroscopic binaries (SB2), which offer a unique laboratory where both components share an identical age and initial chemical composition. Aoki et al. (2022) identified seven VMP SB2 dwarf/turn-off star candidates. Li abudances can be determined separately for each component, which enable us to examine the dependence of possible depletion depending on stellar mass. We report on the radial velocity measurements combining archival Subaru/HDS spectra with new monitoring for these candidates obtained with GAOES/RV, installed at Seimei Telescope, Okayama Observatory. In our binary samples, we already have one sample which orbital elements were previously determined and chemical abundance analysis in progress. Our Seimei monitoring campaign has already yielded a significant result: the confirmation of a short-period VMP binary system (P∼8 days), for which we expect to obtain full coverage RV data soon. Furthermore, we present the detection of Lithium absorption line of either primary/both component in two binaries based on Subaru/HDS data. By combining these new orbital solutions with detailed chemical abundance analysis, we will obtain high-precision masses and Lithium abundances, offering new empirical constraints on stellar depletion mechanisms in the early universe.