| Abstract : | The evolutionary paths taken by very massive stars, M > 60 M , remain substantially uncertain: they begin their lives as main sequence O stars, but, depending on their
masses, rotation rates, and metallicities, can then pass through a wide range of evolutionary
states, yielding an equally broad set of possible surface compositions and spectral classifications. The surface enrichment of He and N is quite common in rotating WNL stars, but the
observed WNL-like surface elemental abundances in slow rotators puzzled astronomers for almost two decades. Previous findings hypothesized that an exotic scenario of stellar spin-down
needs to be invoked in order to explain the origin of these unusually high surface enriched
slow rotators. Contrary to this hypothesis, I will present a different origin mechanism for
WNL stars that these nonrotating metal-rich stars reveal the products of nucleosynthesis
on their surfaces because even modest amounts of mass loss expose their “fossil”-convective
cores: regions that are no longer convective, but which were part of the convective core at
an early stage in the star’s evolution. This mechanism provides a natural explanation for the
origin of metal-rich ([Fe/H] ≥ −1.0) slowly-rotating WNL stars without any need for exotic
spin-downs. |
