Modeling Lithium Depletion in Spite Plateau Stars using MESA

The theory of Big Bang Nucleosynthesis (BBN) provides an explanation for the origin of light elements during the first few moments of the universe. Though this theory corresponds well with observational measurements of light elements, this agreement breaks down in the observation of ⁷Li in old, low-metallicity HALO stars. This disagreement, dubbed the "Lithium problem," poses a roadblock for BBN; if a solution is not found, BBN must be revisited. My research explores solutions to the lithium problem which do not force us to reconsider BBN. Instead we explore potential solutions which rely on thermonuclear destruction of lithium within a star, the most intriguing of which convective overshoot and mixing length theory (MLT), over the 10¹⁰ year lifetime of the star. To test these solutions, I employ the code Modules for Experimentation in Stellar Astrophysics (MESA), a 1D stellar evolution code. I use this code to generate models of stars matching stellar properties of Spite plateau stars from Norris et.al. [1]. We impose astrophysical schemes on these models, and explore various scenarios to induce gradual thermonuclear destruction of ⁷Li bringing its abundance closer to the value predicted by BBN. In particular, we show that the observed lithium resides in a thin surface convective layer for which gradual mixing into the interior is possible.

[1] "A Critique of the Spite Plateau, and the Astration of Primordial Lithium," J. E. Norris et. al., MNRAS, 522, 1358 (2022), arXiv:2303.11297 [astro-ph.SR].