Contributed Talk - Splinter Stellar

Friday, 25 September 2020, 11:38   (virtual room M)

On the nature of WR-type mass loss in different environments

Andreas Sander, Jorick Vink
Armagh Observatory & Planetarium

Classical Wolf-Rayet (WR) stars are hydrogen-poor massive stars with prominent emission lines. They are therefore often used as benchmarks for massive helium (He) stars in stellar populations. However, their occurrence depends strongly on their environment, in particular on the metallicity (Z). Until now, our theoretical understanding of their feedback is rather fragmentary, hampering robust predictions about stellar populations and the occurrence of WR-type mass loss. To develop a fundamental understanding of mass loss in massive He stars, we employ a new generation of model atmospheres including a consistent solution of the wind hydrodynamics. This way, we can study the ingredients of He-star winds and unveil the nature of WR-type mass loss. Our results reveal a complex picture with strong, non-linear dependencies on the luminosity-to-mass ratio and Z. Moreover, they provide a theoretical motivation for a population of He stars at low Z, which cannot be detected via WR-type spectral features. The talk will briefly outline the challenges of understanding hydrogen-depleted massive stars and the underlying concept of next-generation stellar atmospheres. Moreover, we present and discuss the results from our groundbreaking study of massive He-star models, yielding the very first mass-loss recipe derived from first principles in this regime. We finish by outlining observational implications of our study including the need to correctly understand the manifold impacts of the presence and absence of WR-type mass-loss in the Universe.