Structure and evolution of single WR stars

Abstract

New computations of massive stars follow the evolution up to advanced stages and include:

• -A large and flexible nuclear network consisting of 174 nuclear species that are linked by 1742 nuclear reactions.

• -Semiconvection, overshooting and mass loss.

• -Modern rates for both strong and weak interaction processes as well as the latest rates for the neutrino processes.

• -Improved grid distribution and a large number of grid points.

The nuclear network and the diffusion equation are solved for each time step during the whole evolution. In this way the accuracy of nuclear yields and chemical abundances are mainly limited by uncertainties in the diffusion coefficient found from the convection theories.

Several instability mechanisms may affect the mass loss rates of massive stars and thereby the structure and abundances of WR stars. Due to heavy mass loss at the LBV and WR stages, the masses at the pre-SN stage may be less than 5M _⊙. Yields and abundances throughout the stars are discussed together with the amount of all elements expelled.