Probing Binary Architectures of Lithium-Rich Giants in GALAH with COSMIC and Stellar Models
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| Formato: | Preprint |
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2025
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| _version_ | 1866916831552339968 |
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| author | Sayeed, Maryum Yang, Selina Cinquegrana, Giulia Ness, Melissa K. Breivik, Katelyn Casey, Andrew R. Buder, Sven Karakas, Amanda I. |
| author_facet | Sayeed, Maryum Yang, Selina Cinquegrana, Giulia Ness, Melissa K. Breivik, Katelyn Casey, Andrew R. Buder, Sven Karakas, Amanda I. |
| contents | 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 $s=3.3\pm0.5 \rm \; AU$ 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_05359 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Probing Binary Architectures of Lithium-Rich Giants in GALAH with COSMIC and Stellar Models Sayeed, Maryum Yang, Selina Cinquegrana, Giulia Ness, Melissa K. Breivik, Katelyn Casey, Andrew R. Buder, Sven Karakas, Amanda I. Solar and Stellar Astrophysics Astrophysics of Galaxies 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 $s=3.3\pm0.5 \rm \; AU$ 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. |
| title | Probing Binary Architectures of Lithium-Rich Giants in GALAH with COSMIC and Stellar Models |
| topic | Solar and Stellar Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2507.05359 |