2. Numerical method and physical assumptions
Our calculations have been performed with a hydrodynamic stellar evolution code (cf., Langer 1998, and references therein), which has been upgraded to include angular momentum, the effect of the centrifugal force on the stellar structure, and rotationally induced transport of angular momentum and chemical species due to Eddington-Sweet circulations, the Solberg-Hoiland and Goldreich-Schubert-Fricke instability, and the dynamical and secular shear instability. We apply the rotational physics exactly as in Heger et al. (1999). In particular, the effects of gradients of the mean molecular weight µ, which pose barriers to any mixing process, have been included as in Heger et al. (i.e., ). As in Heger et al., we have also included the effects of µ-barriers on convection by using the Ledoux-criterion for convection and semiconvection according to Langer et al. (1983), which is consistent with our treatment of the rotational mixing (Maeder 1997).
Changes of the chemical composition and the nuclear energy generation rate are computed using nuclear networks for the three pp-chains, the four CNO-cycles, and the NeNa- and the MgAl-cycle. Further, the 3-reaction is included, and (,)-reactions on 12C, , , 19F, , , and (,n)-reactions on 13C, 17O, , . The inclusion of (n,)-reactions on 12C, , , allows an order of magnitude estimate of the neutron concentration. For more details see Heger et al. (1999) and Heger (1998).
© European Southern Observatory (ESO) 1999
Online publication: June 17, 1999