The Mechanism Investigation on the Superwind and Thermal Pulse in the AGB Star

The theoretical investigations on the superwind and thermal pulsation in the AGB star so far are based on the neglecting theturbulent pressure. How ever, for an AGB star with complete convectiv eenv elope the turbulent pressure exists and has important influence on the gaspressure, density, tempera ture and the ther modynamical quanti ties. Therefore, the existence of the turbulent perssure must influence on the superwind and thermal pulse in the AGB star. In this thesis we have derived the expressions of the turbulent pressure, the state equation and the thermody namical quanti ties based on the mixing lengh covection theory and given a criterion for the occurrence of the dy namical instability in the convective envelope. In order to investiga te the effects of turbulent pressure on the superwind and thermal pulse in the AGB star, the evolution of the stars with mass of 2.8M⊙ and 7M⊙ from the main sequence to the AGB stage has calculated respectively. The results show that the turbulent pressure can be 30 percent of the total pressure in the regions closed to the surface of an AGB star with 7M⊙and has an important influence on the innerst ructure and evolution. Owing to the effect of turbulent pressure the regions closed to the surface of AGB star and redgiant star are insta bledynamically. This causes an outwards mass ejection which forms the superwind in the AGB star or the strong stellar wind in the red giant star. Due to the effect of the turbulent pressure, the thermal pulse in the He-burning shell occurs early and its period becomes shorter.