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Physical Properties of Wolf-Rayet Stars

Unknown author(s)

Annual Review of Astronomy and Astrophysics · 2007 · 979 citations · 161 references

Open access

TL;DR

Wolf‑Rayet stars exhibit unusually broad emission lines that have long challenged analysis due to the extreme physical conditions in their line‑forming regions. Recent model‑atmosphere studies now enable determination of temperatures, luminosities, abundances, ionizing fluxes, and wind properties, while binary systems provide a laboratory for wind‑wind interactions and dust formation in WC stars. Observed WN and WC star distributions imply progenitor mass thresholds of ~25, 40, and 75 M⊙ for He‑burning WN, WC, and H‑burning WN stars, respectively, with typical WR masses of 10–25 M⊙ (up to 80 M⊙ for H‑rich WN) and evidence that metallicity‑dependent winds affect evolutionary models, ionizing output, and the roles of WR stars in core‑collapse supernovae and long‑duration gamma‑ray bursts.

Abstract

The striking broad emission line spectroscopic appearance of Wolf-Rayet (WR) stars has long defied analysis, owing to the extreme physical conditions within their line- and continuum-forming regions. Recently, model atmosphere studies have advanced sufficiently to enable the determination of stellar temperatures, luminosities, abundances, ionizing fluxes, and wind properties. The observed distributions of nitrogen- (WN) and carbon (WC)-sequence WR stars in the Milky Way and in nearby star-forming galaxies are discussed; these imply lower limits to progenitor masses of ∼25, 40, and 75 M ⊙ for hydrogen-depleted (He-burning) WN, WC, and H-rich (H-burning) WN stars, respectively. WR stars in massive star binaries permit studies of wind-wind interactions and dust formation in WC systems. They also show that WR stars have typical masses of 10–25 M ⊙ , extending up to 80 M ⊙ for H-rich WN stars. Theoretical and observational evidence that WR winds depend on metallicity is presented, with implications for evolutionary models, ionizing fluxes, and the role of WR stars within the context of core-collapse supernovae and long-duration gamma-ray bursts.