Rotating Stellar Structure And Evolution

Stellar rotation is a difficult problem of the theory of stellar structure and evolution. Recent observational dates, especially observational dates of the early type stars indicate that some efficient mixing processes might be induced by rotation. Thus, the study of evolution of rotating stars has attracted more and more attention in the last decades.The stellar structure and evolution model will be two dimensional due to the effects of rotation, but many scientists have tried to simplify the two dimensional stellar structure and evolution model to one dimensional. Their ways of dealing this problem are reviewed, and a relative simple way is proposed, this way is based on the following assumption: physical quantities such as temperature, density, pressure, luminosities, chemical composition and angular velocities are nearly the same on the equipotential surfaces, and they are equal to their counterparts on the equivalent sphere. (The equivalent sphere is an imaginary sphere, the volume enclosed by it is equal to the volume enclosed by the equipotential surface) We derive the new structure and evolution equations of rotating stars by using the quantities of an point on the equivalent sphere, and construct a new model. Comparing with the non-rotating model, it has the following changes: the change in the hydrostatic equation; the change in the radiation temperature gradient and the criterion of convection, and the enhancement of stellar wind and angular momentum loss.As the application of our new rotating model, we study the main factors which affecting the formation and extension of the blue loops of the middle and low massstars. It is interesting to notice that although rotation and overshooting can both affect the length of the blue loops, their effects are appreciably different. Hence, a comparison of the differences between the inner structure of a star affected by rotation and overshooting can isolate those factors, which play a primary role in the formation and extension of the blue loops. We find that the feature of blue loops is correlated to the variation of the total energy production rate of the star during the core He-burning. When the variation of the total energy production rate is contributed mainly by the H-burning shell, the formation and extension of the blue loops is dependent, however, on the temperature and the hydrogen profile in the u-gradient region and the inward penetration of the outer convective zone. When the variation of the total energy production rate is contributed by both of the H-burning shell and the core He-burning, the formation and extension of the blue loops is dependent not only on the properties of the u-gradient region, but also on both of the size of the He core and the temperature in the region of the He core.In the present paper, some physical effects of rotation have been discussed, however, they will be studied in detail later.