It is shown that a moderate increase of the opacity due to heavy elements in models of massive stars, incorporating convective overshoot and mass loss by stellar wind, can remove the well known discrepancy between theoretical expectation and observed frequencies of luminous stars in the HR diagram. These models in fact extend their main sequence band far beyond the classical limit.

Evidence for a Large Main Sequence Widening: A Plea for Overshooting and Higher Heavy-Element Opacity

In this paper we present recent calculations of stellar structure in which the effects of convective overshooting are taken into account during the core H- and He-burning phases of stars in the mass range 1.3 M⊙ to 100 M⊙. In addition to this, we briefly review the effects of mass loss in luminous stars of all spectral types, and in red giant and asymptotic giant branch stars. Finally, the effects of the novel cross section for the 12C(α,γ)16O nuclear reaction are also illustrated.

Advancements in the Stellar Evolution Theory: The Role of Convective Overshooting All Across the HR Diagram

Atmospheric diagnostics of Wolf-Rayet stars

Atmospheres and interior models

Evolutionary tracks are computed for massive stars with masses between 10 and 100 M⊙ for the Galaxy and the Magellanic Clouds. The extent of the convective cores is determined by the Roxburgh criterion for convection, implying overshooting from convective cores. By comparing the observed upper boundary to the luminosity of late-type supergiants to observations, we determine the dependence of the mass-loss rate on the metallicity. It turns out that this dependence is weak. The influence of varying metallicity on the formation of Wolf-Rayet stars is discussed.

Stellar Evolution in the Magellanic Clouds

With the assumption of planparallel hydrostatic atmospheres, used generally for the computation of evolutionary models, the radii of WR stars are seriously underestimated. The true atmospheres may be very extended, due to the effect of the stellar wind. Instead of these hydrostatic atmospheres we consider dynamical atmospheres adopting a velocity law. The equation of the optical depth is integrated outwards using the equation of continuity.

C. De Loore

Papers

Corrections for Hydrostatic Atmospheric Models: Radii and Effective Temperatures of Wolf Rayet Stars