The Wolf-Rayet Stellar Response To The Iron Opacity Bump: Envelope Inflation, Winds, and Microturbulence

Abstract

Early-type Wolf-Rayet(WR) stellar models harbor a super-Eddington layer in their outer envelopes due to a prominent iron opacity bump. In the past few decades, one-dimensional hydrostatic and time-steady hydrodynamic models have suggested a variety of WR responses to a super-Eddington force including envelope inflation and optically thick winds. In this paper, I study these responses using semianalytical estimates and WR models from both MESA and Ro & Matzner; four conclusions are present. First, early-type WR stars do not harbor inflated envelopes because they have either strong winds or insufficient luminosities. Second, the condition for an opacity bump to harbor a sonic point is expressible as a minimum mass-loss rate, ${\dot{M}}_{\mathrm{sp}}(L_{\ast })$. In agreement with Grassitelli et al. and Ro, the majority of galactic early-type WR stars can harbor sonic points at the iron opacity bump. However, about half of those in the Large Magellanic Cloud cannot given typical wind parameters. Third, WR winds driven by the iron opacity bump must have mass-loss rates that exceed a global minimum of $10^{-5.8}-10^{-6}{M}_{\odot }{\mathrm{yr}}^{-1}$. Lastly, the observed early-type WR distribution follows a simple mass-loss relation derived here if the radiation-to-gas pressure ratio is approximately $p_r/p_g\sim 145$ in the wind; a value consistent with studies by Grafener et al. and Nakauchi & Saio.

10 pages, 6 figures

References in corpus (10)

• Physical Properties of Wolf-Rayet Stars
• The Galactic WN stars: Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
• The Galactic WC stars: Stellar parameters from spectral analyses indicate a new evolutionary sequence
• On the consistent treatment of the quasi-hydrostatic layers in hot star atmospheres
• Common envelope ejection in massive binary stars - Implications for the progenitors of GW150914 and GW151226
• Towards a better understanding of the evolution of Wolf-Rayet stars and Type Ib/Ic supernova progenitors
• A new prescription for the mass-loss rates of WC and WO stars
• On the optically-thick winds of Wolf-Rayet stars
• Extended supernova shock breakout signals from inflated stellar envelopes
• Helium-Star Models with Optically Thick Winds: Implications for the Internal Structures and Mass-Loss Rates of Wolf-Rayet Stars

Cited by in corpus (10)

• On the nature of massive helium star winds and Wolf-Rayet-type mass loss
• Driving classical Wolf-Rayet winds: A Γ- and Z-dependent mass-loss
• Wind-envelope interaction as the origin of the slow cyclic brightness variations of luminous blue variables
• The temperature dependency of Wolf-Rayet-type mass loss: An exploratory study for winds launched by the hot iron bump
• Tidal Spin-up of Black Hole Progenitor Stars
• The SOUX AGN sample: Optical/UV/X-ray SEDs and the nature of the disc
• A spectroscopic multiplicity survey of Galactic Wolf-Rayet stars. III. The northern late-type nitrogen-rich sample
• Hydrogen-free Wolf-Rayet stars: Helium stars with envelope-inflation structure and rotation
• Multiple variability time-scales of the early nitrogen-rich Wolf-Rayet star WR7
• Methods to Test the Source of the Extreme Gas Motions in WS 35