Hydrodynamics, nucleosynthesis, and mass loss in massive stars

Abstract

I test the predictive power of the stellar evolution code TYCHO. Systematic errors are present in the predictions for double-lined eclipsing binary stars when only standard physics common to the majority of stellar evolution codes is included. A mechanism for driving slow circulation and mixing in the radiative regions of stars is identified in numerical simulations of convection and a physical theory developed. Mixing is caused by dissipation of inertial waves driven by the interaction of convective fluid motions with the boundary of the convection zone. Evolutionary calculations incorporating this physics are tested in several observational regimes. Light element depletion in young clusters, turnoff ages of young clusters with brown dwarf Li depletion ages, and evolution of carbon stars on the asymptotic giant branch are all predicted satisfactorily. Tests of solar models yield good agreement with surface observables, chemical abundances, helioseismological data, and neutrino fluxes. The predictive accuracy of a non-calibrated, state-of-the-art stellar evolution code is ∼7% for surface observables. The main sequence sun is relatively easy to model, so this gives an estimate of our minimum predictive error. The solar models also highlight problems with uniqueness of evolutionary tracks converging on a given point and the potential for avoiding the effects of missing physics by calibration. A reanalysis of the binary sample with the more complete physics shows a dramatic improvement in the accuracy of the models. The potential for avoiding the effects of missing physics by calibration is explored. A TYCHO model for a late AGB star is used for the boundary conditions on a hydrodynamic simulation of proto-planetary nebula evolution as an illustration of the unified technique. NaCl and NaCn are observed at large radii in the Egg Nebula. These molecules require high densities to form, which are difficult to explain at large distances from the star. The 2-D simulation of a fast wind interacting with earlier mass loss produces clumps of material through a thermal instability with the necessary conditions for formation of the molecules. In conclusion, the effects of the more complete physics on the core size and abundance profiles of a massive star during core Si burning are examined as an example of future developments.