ESPRESSO Radial Velocity Survey Finds No Excess Close Binaries Among Lithium-Rich Giants

The Torres et al. preprint reports four or more RV epochs over seven months for 32 red-clump and 25 RGB lithium-rich targets. After subtracting expected jitter, 11 RC and 8 RGB stars show variability consistent with companions having periods shorter than 3000 days; only three are confirmed stellar-mass. Monte Carlo modeling separates stellar from sub-stellar probabilities, but the distributions remain statistically indistinguishable between evolutionary stages, directly testing the binary-interaction channel proposed for lithium enrichment.

Prior work, including the 2022 Gaia-based binary census by Singh et al. and the 2023 RV monitoring of 200 lithium-normal giants by the APOGEE team, established a close-binary fraction of roughly 25-35% for field red giants at similar metallicities. The new lithium-rich sample sits squarely within this range, weakening the hypothesis that binary mass transfer or merger dominates lithium production and shifting attention to internal mixing or planet-engulfment scenarios.

The current seven-month baseline is insensitive to orbits beyond 3000 days, leaving open the possibility that wider companions still contribute. Extending the campaign to three years, as the authors propose, will test whether the cumulative binary fraction rises above the lithium-normal benchmark or remains flat, providing a decisive constraint on stellar-evolution models.

The study underscores how targeted RV campaigns on chemically peculiar stars can falsify enrichment channels without requiring full orbital solutions, provided sample sizes and temporal coverage are adequate.