A Theoretical Study of the Structure and Elemental Abundances of HD 20794

Abstract HD 20794 is a nearby, bright, and well-studied metal-poor G-type dwarf hosting a compact multi-planet system, including a super-Earth located near the habitable zone. Its low stellar activity and the availability of high-precision radial-velocity and photometric data make it a valuable benchmark for testing stellar structure models and chemical abundance interpretations in low-metallicity planet-hosting stars. To our best knowledge, we present the first grid-based stellar modelling analysis of HD 20794 using the Modules for Experiments in Stellar Astrophysics (MESA), focusing on its main-sequence and late main-sequence evolution. We computed 252 stellar evolutionary models with initial masses between 0.78 and 0.80 M⊙, systematically varying the convection efficiency, numerical resolution, and atmospheric boundary conditions. We selected the models by performing a χ2-based comparison with the observed effective temperature, surface gravity, luminosity, radius, and age. The best-fitting models adopt a stellar mass of 0.80 M⊙ and an age of approximately 9 Gyr, and reproduce all observed stellar parameters within their uncertainties. In particular, the models successfully reproduce the observed surface abundance pattern of HD 20794 for a wide range of elements, including light elements, α-elements, and the odd-Z species phosphorus and chlorine. Comparisons with published massive-star nucleosynthesis yields suggest that the observed phosphorus and chlorine abundances are consistent with enrichment from core-collapse supernovae and have been preserved throughout the star’s evolution. Our results are consistent with standard stellar evolution theory, indicating that low-mass, metal-poor G-type dwarfs such as HD 20794 retain their natal chemical signatures over Gyr timescales, providing valuable constraints on stellar evolution, Galactic chemical enrichment, and the chemical environments of long-lived planetary systems.