Name: Arpita Roy
Affiliation: Scuola Normale Superiore, Pisa, Italy
Conference ID : ASI2022_140
Title : A new mechanism for the origin of WNL stars: exposure of "fossil"-convective cores
Authors : Author: Arpita Roy. Co-authors: Mark Krumholz, Ralph Sutherland, Alexander Heger, Michael Dopita
Abstract Type: Oral
Abstract Category : Stars, ISM and Galaxy
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.