Helium-Star Models with Optically Thick Winds: Implications for the Internal Structures and Mass-Loss Rates of Wolf-Rayet Stars

Abstract

We construct helium (He) star models with optically thick winds and compare them with the properties of Galactic Wolf-Rayet (WR) stars. Hydrostatic He-core solutions are connected smoothly to trans-sonic wind solutions that satisfy the regularity conditions at the sonic point. Velocity structures in the supersonic parts are assumed by a simple beta-type law. By constructing a center-to-surface structure, a mass-loss rate can be obtained as an eigenvalue of the equations. Sonic points appear at temperatures ~ 1.8e5 - 2.8e5 K below the Fe-group opacity peak, where the radiation force becomes comparable to the local gravity. Photospheres are located at radii 3-10 times larger than sonic points. The obtained mass-loss rates are comparable to those of WR stars. Our mass-loss rate - luminosity relation agrees well with the relation recently obtained by Graefener et al. (2017). Photospheric temperatures of WR stars tend to be cooler than our predictions. We discuss the effects of stellar evolution, detailed radiation transfer, and wind clumping, which are ignored in this paper.

18 pages, 23 figures, accepted for publication in the Astrophysical Journal

References in corpus (11)

• The Gaia mission
• Physical Properties of Wolf-Rayet Stars
• Mass loss from hot massive stars
• The Galactic WN stars: Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
• Mass loss from late-type WN stars and its Z-dependence: very massive stars approaching the Eddington limit
• The Galactic WC stars: Stellar parameters from spectral analyses indicate a new evolutionary sequence
• Towards a better understanding of the evolution of Wolf-Rayet stars and Type Ib/Ic supernova progenitors
• Interpretation of the BRITE oscillation data of the hybrid pulsator $\nu$ Eridani: a call for the modification of stellar opacities
• A new prescription for the mass-loss rates of WC and WO stars
• On the optically-thick winds of Wolf-Rayet stars
• Do Stellar Winds Prevent the Formation of Supermassive Stars by Accretion?