Subsonic structure and optically thick winds from Wolf--Rayet stars

Abstract

Wolf-Rayet star's winds can be so dense and so optically thick that the photosphere appears in the highly supersonic part of the outflow, veiling the underlying subsonic part of the star, and leaving the initial acceleration of the wind inaccessible to observations. We investigate the conditions and the structure of the subsonic part of the outflow of Galactic WR stars, in particular of the WNE subclass; our focus is on the conditions at the sonic point. We compute 1D hydrodynamic stellar structure models for massive helium stars adopting outer boundaries at the sonic point. We find that the outflows of our models are accelerated to supersonic velocities by the radiative force from opacity bumps either at temperatures of the order of 200kK by the Fe opacity bump or of the order of 50kK by the HeII opacity bump. For a given mass-loss rate, the conditions in the subsonic part of the outflow are independent from the detailed physical conditions in the supersonic part. The close proximity to the Eddington limit at the sonic point allows us to construct a Sonic HR diagram, relating the sonic point temperature to the L/M ratio and the stellar mass-loss rate, thereby constraining the sonic point conditions, the subsonic structure, and the stellar wind mass-loss rates from observations. The minimum mass-loss rate necessary to have the flow accelerated to supersonic velocities by the Fe opacity bump is derived. A comparison of the observed parameters of Galactic WNE stars to this minimum mass-loss rate indicates that their winds are launched to supersonic velocities by the radiation pressure arising from the Fe-bump. Conversely, models which do not show transonic flows from the Fe opacity bump form inflated envelopes. We derive an analytic criterion for the appearance of envelope inflation in the subphotospheric layers.

arXiv commentA&A, Forthcoming article. 13 pages+5

References in corpus (41)

• Mass-loss predictions for O and B stars as a function of metallicity
• Presupernova Evolution of Rotating Massive Stars I: Numerical Method and Evolution of the Internal Stellar Structure
• Pre-Supernova Evolution of Massive Single and Binary Stars
• Acoustic black holes: horizons, ergospheres, and Hawking radiation
• Mass loss from hot massive stars
• Single star progenitors of long gamma-ray bursts I: Model grids and redshift dependent GRB rate
• On the metallicity dependence of Wolf-Rayet winds
• The Galactic WN stars: Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
• Grids of stellar models with rotation II. WR populations and supernovae/GRB progenitors at Z = 0.014
• The Galactic WC stars: Stellar parameters from spectral analyses indicate a new evolutionary sequence
• Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates
• Stellar envelope inflation near the Eddington limit. Implications for the radii of Wolf-Rayet stars and luminous blue variables
• The evolution of rotating very massive stars with LMC composition
• Massive main sequence stars evolving at the Eddington limit
• The spectroscopic Hertzsprung-Russell diagram
• Local Radiation Hydrodynamic Simulations of Massive Star Envelopes at the Iron Opacity Peak
• The VLT-FLAMES Tarantula Survey XVII. Physical and wind properties of massive stars at the top of the main sequence
• Hydrodynamic model atmospheres for WR stars: Self-consistent modeling of a WC star wind
• Core-halo Structure of Chemically Homogeneous Massive Star and Bending of Zero-Age Main-Sequence
• Clumping in the inner winds of hot, massive stars from hydrodynamical line-driven instability simulations
• Coupling hydrodynamics with comoving frame radiative transfer: I. A unified approach for OB and WR stars
• Local Radiative Hydrodynamic and Magnetohydrodynamic Instabilities in Optically Thick Media
• The metallicity dependence of envelope inflation in massive stars
• A consistent solution for the velocity field and mass-loss rate of massive stars
• Very Massive Stars in the Local Universe
• Explosion and nucleosynthesis of low redshift pair instability supernovae
• Observational consequences of turbulent pressure in the envelopes of massive stars
• On magnetic inhibition of photospheric macro-turbulence generated in the iron-bump opacity zone of O-stars
• A Systematic Search for Corotating Interaction Regions in Apparently Single Galactic WR Stars. I. Characterizing the Variability
• Helium Stars: Towards an Understanding of Wolf-Rayet Evolution
• On the optically-thick winds of Wolf-Rayet stars
• Mass fluxes for O stars
• Instabilities in the Envelopes and Winds of Very Massive Stars
• WR 110: A Single Wolf-Rayet Star With Corotating Interaction Regions In Its Wind?
• Inferring hot-star-wind acceleration from Line Profile Variability
• Diagnostic of the unstable envelopes of Wolf-Rayet stars
• On the Launching and Structure of Radiatively Driven Winds in Wolf-Rayet Stars
• Metallicity dependence of turbulent pressure and macroturbulence in stellar envelopes
• On the origin of variable structures in the winds of hot luminous stars
• The structure of line-driven winds
• Helium-Star Models with Optically Thick Winds: Implications for the Internal Structures and Mass-Loss Rates of Wolf-Rayet Stars

Cited by in corpus (26)

• On the nature of massive helium star winds and Wolf-Rayet-type mass loss
• The Galactic WC and WO stars: The impact of revised distances from Gaia DR2 and their role as massive black hole progenitors
• Theory and Diagnostics of Hot Star Mass Loss
• First 3D Radiation-Hydrodynamic Simulations of Wolf-Rayet Winds
• 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
• Evolution of Wolf-Rayet stars as black hole progenitors
• Numerical experiments to help understand cause and effect in massive star evolution
• Physics and evolution of the most massive stars in 30 Dor. Mass loss, envelope inflation, and a variable upper stellar mass limit
• Wind nebulae and supernova remnants of very massive stars
• The Shortest-period Wolf-Rayet binary in the Small Magellanic Cloud: Part of a high-order multiple system
• Dynamically inflated wind models of classical Wolf-Rayet stars
• A spectroscopic multiplicity survey of Galactic Wolf-Rayet stars. III. The northern late-type nitrogen-rich sample
• The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud: spectroscopy, orbital analysis, formation, and evolution
• Exploring the influence of different velocity fields on Wolf-Rayet star spectra
• PION: Simulating bow shocks and circumstellar nebulae
• Wind suppression by X-rays in Cygnus X-3
• The Wolf-Rayet Stellar Response To The Iron Opacity Bump: Envelope Inflation, Winds, and Microturbulence
• Spectroscopic and evolutionary analyses of the binary system AzV 14 outline paths toward the WR stage at low metallicity
• The Physical Parameters of Four WC-type Wolf-Rayet Stars in the Large Magellanic Cloud: Evidence of Evolution
• BAT99-9 -- a WC4 Wolf-Rayet star with nitrogen emission: Evidence for binary evolution?
• Inverse Compton cooling of thermal plasma in colliding-wind binaries
• Hydrogen-free Wolf-Rayet stars: Helium stars with envelope-inflation structure and rotation
• Metal-poor single Wolf-Rayet stars: The interplay of optically thick winds and rotation
• Dynamically consistent analysis of Galactic WN4b stars
• Polarization of light from fast rotating Wolf-Rayet stars: A Monte Carlo simulations compared to analytical formula