2025/07/07 by Maryum Sayeed, Selina F. Yang, Sayeed, Maryum +13 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Scientific Research and Discoveries #Solar and Stellar Astrophysics (astro-ph.SR) #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2507.05359
openalex publication_date 2025/07/07 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Surface lithium is depleted when a star goes through the first dredge-up phase, yet 1% of red giants are found to be Li-rich. The formation mechanism for these remains uncertain. We combine observational constraints from GALAH Li-rich giants, with the binary population synthesis code COSMIC to investigate system properties of these objects assuming binary mass transfer. By evolving 9 million binary systems, we find that binary histories most consistent with observational constraints are mass transfer from an intermediate-mass AGB donor to a main-sequence star now observed as a Li-rich red giant. In GALAH, 9% of main-sequence stars have \rm A(Li)=2.5-3.2 dex making it plausible to create red giants with \rm A(Li)=1.5-2.2 dex via main-sequence mass transfer, but cannot explain the more enriched giants \rm A(Li) \gtrsim 2.2 dex. Nucleosynthetic yields from stellar models show that AGB stars with initial masses of 4.25-5 \rm M_\odot and 8 \rm M_\odot contain the most Li in their ejecta. Intermediate-mass AGB stars comprise 29% of COSMIC results, with present-day separations s=3.3±0.5 \rm AU and mass ratios q=0.5-1.6. We achieve 95% agreement in mean enhancements in \rm (Ba, Y) between GALAH observations and stellar models of 6 and 8 \rm M_\odot AGB, assuming 1% mass transfer efficiency. We find a low mass transfer efficiency best reproduces GALAH observations suggesting that the preferred mass transfer mechanism for Li-enrichment is via wind Roche Lobe Overflow. While we constrain the most plausible binary parameters assuming AGB mass transfer creates Li-rich giants, discrepancies in nucleosynthesis comparisons, and the small fraction of Li-enhanced main-sequence stars suggests additional enrichment mechanisms are likely.