Mechanism of helium enrichment in hydrogen-enriched WN stars

Determine the physical mechanism responsible for helium enrichment in the surface layers of hydrogen-enriched WN stars (spectral types WN5–7h and WN5–7ha), assessing whether the enrichment is caused primarily by significant mass loss through powerful stellar winds or by rotationally induced internal mixing.

Background

The authors summarize that very luminous, hydrogen-enriched WN stars differ from classical Wolf–Rayet stars and exhibit helium-enriched surfaces while likely being comparatively young and core hydrogen-burning. They note that the origin of this helium enrichment is debated in the literature.

Two leading hypotheses are cited: (i) substantial mass loss via strong winds, and (ii) mixing of interior material driven by rapid axial rotation. Discriminating between these mechanisms remains unresolved.