The study of the Evolution of rotating Massive Pop III Stars at the stage of core H and He burning

We investigate the effects of rotation on the evolution of Population III (Pop III) stars at the stage of core H and He burning. Due to their zero-metallicity nature, these stars are initially unable to burn hydrogen through the CNO cycle. And without this crucial energy supply, they experience a contraction phase during the early main sequence(MS). The lack of CNO elements not only affects the central regions of the star but also leads to energy increase (due to triggering of the CNO cycle) in the stellar envelope due to the outward diffusion of He-burning products. Therefore, rotational mixing has a unique impact on these stars. · Rotation significantly affects the observable properties of Pop III stars through two main effects. Firstly, rotational mixing brings additional fuel into the nuclear burning core, which increases the luminosity as well as the stellar lifetimes. Secondly, rotational mixing brings He-burning products from the core to the H-burning shell during later evolutionary phases. This changes the temperature profile, and can lead to significant expansion in some models depending on the relative core size. The relative core size is crucial here, because the contribution of the shell and the core to the total energy produced tells us about the structure of the star and what dominates with regard to the evolution of the surface properties. · Despite weaker meridional currents in Pop III stars, angular momentum can accumulate at the surface in fast-rotating massive models because of their negligible mass loss through radiative winds. This spin-up brings models with an initial mass of 40M⊙, initial velocity of υini=400km/s and metallicity of Z=10⁻⁴ to critical rotation during the MS which leads to increased mass loss. · Rotational mixing strongly affects metal enrichment, but does not consistently enhance metal production, different from stars with high metallicity. Rotation leads to an earlier CNO boost to the H shell during He burning, which may hinder metal enrichment. This is true for the core He-burning phase. In these cases the triggering of convection by the CNO boost in the H shell causes a retraction of the He-burning core. As the core grows, the H shell moves outwards faster than the He-burning products can be expelled from the core through rotational mixing, therefore hindering the interaction of these products with the H-burning shell, which is required for metal enrichment. H-He shell interactions after core He burning play a crucial role in metal production, where rotation may enhance enrichment. This highlights the complexity in the metal enrichment processes of these models. A detailed understanding of the interior structure is therefore required to accurately predict metal yields.