恒星物理研究组知识库

The aim of this paper is to investigate the effect of rotation on the single and binary evolution for Population III stars. A small grid for a massive Population III star of 130 M is constructed, and various initial conditions are adjusted to explore the evolution. For comparison, we present the evolution of the models with the metallicity in the Small Magellanic Cloud and analyze the characteristic feature of chemically homogeneous evolution. It is found that Population III stars attain the equilibrium velocities later during synchronization owing to a smaller radius. The equilibrium velocity has been expressed as various timescales. There appears to be a deep dredge-up at hydrogen exhaustion for single Population III stars. It not only increases the helium core but also exchanges chemical elements between the He core and the H-burning shell. This will give rise to a significant amount of nitrogen and neon. Rotational mixing can reduce the specific entropy in the envelope and increase the specific entropy in the core owing to a change of mean molecular weight. Stellar compactness and the luminosity available for stellar expansion are decreased by rotational mixing because of the increase of helium in the envelopes. Mass loss induced by strong stellar winds and Roche lobe overflow can extinguish the hydrogen-burning shell and remove convective envelopes. Therefore, this process does not favor the dredge-up and production of primary nitrogen. The chemical structure for two components in binarities is significantly modified because Roche lobe overflow has an impact on convective cores.