The influence of turbulent pressure on the late stages of evolution of low- and intermediate-mass star. (I). Calculations for turbulent pressure, the equation of state and the thermodynamic quantities.

Based on the mixing-length theory of convection, expressions are derived for (1) the turbulent pressure, and (2) the equation of state as well as the thermodynamic quantities by taking turbulent pressure into account. In order to know how great the turbulent pressure could be, the authors performed calculations for the evolution of stars of 2.8 M_sun and 7 M_sun from the main sequence to the red giant and the AGB stages. The results show that the turbulent pressure in the regions close to the surfaces of a red giant and an AGB star can reach a value of 30% of the total pressure.