Using Shell Models to Investigate Clumping in the WN4 Star HD 50896

Abstract

The spectra of Wolf-Rayet (WR) stars exhibit strong, broad emission lines that originate in the wind. These winds are radiatively driven and are susceptible to hydrodynamic instabilities that result in the formation of clumps. When modelling spectra of WR stars the volume-filling factor (VFF) approach is usually employed to treat clumpy winds. However, it is based on the assumption that the entire wind mass resides in optically thin clumps, which is not necessarily justifiable in dense winds. To test the validity of the VFF approach we use a previously described method of treating clumping, the ``Shell'' approach, to study line and continuum formation in the dense wind of the WN4 star, HD 50896. Our models indicate that fully intact spherical shells are in tension with observed spectra; a persistent ``dip'' in emission lines occurs at line centre. Removing this dip requires our models to use ``broken'' shells -- shells that are highly decoherent laterally. This insinuates that the wind of HD 50896, and by extension the winds of other WR stars, are comprised of small laterally confined and radially compressed clumps -- clumps smaller than the Sobolev length. We discuss some of the conditions necessary for the VFF approach to be valid.

18 pages, 17 figures. Accepted for publication in MNRAS

References in corpus (27)

• Bright OB stars in the Galaxy - III. Constraints on the radial stratification of the clumping factor in hot star winds from a combined Halpha, IR and radio analysis
• Revised Stellar Temperatures for Magellanic Cloud O Supergiants from FUSE and VLT-UVES Spectroscopy
• Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates
• Stellar and Wind Properties of LMC WC4 stars - A metallicity dependence for Wolf-Rayet mass-loss rates
• L-band spectroscopy of Galactic OB-stars
• X-ray line emission from a fragmented stellar wind
• 2D wind clumping in hot, massive stars from hydrodynamical line-driven instability simulations using a pseudo-planar approach
• Unlocking Galactic Wolf-Rayet stars with $\text{Gaia}$ DR2 I: Distances and absolute magnitudes
• Atmospheric NLTE-models for the spectroscopic analysis of blue stars with winds. IV. Porosity in physical and velocity space
• X-ray emission lines from inhomogeneous stellar winds
• Mass loss from inhomogeneous hot star winds III. An effective-opacity formalism for line radiative transfer in accelerating, clumped two-component media, and first results on theory and diagnostics
• First 3D Radiation-Hydrodynamic Simulations of Wolf-Rayet Winds
• The impact of rotation on the line profiles of Wolf-Rayet stars
• Empirical mass-loss rates and clumping properties of Galactic early-type O supergiants
• On the Importance of the Interclump Medium for Superionization: O VI Formation in the Wind of Zeta Pup
• XMM-Newton Detection of Hard X-ray Emission in the Nitrogen-Type Wolf-Rayet Star WR110
• A generalised porosity formalism for isotropic and anisotropic effective opacity and its effects on X-ray line attenuation in clumped O star winds
• A 2.3-Day Periodic Variability in the Apparently Single Wolf-Rayet Star WR 134: Collapsed Companion or Rotational Modulation?
• Tides in asynchronous binary systems
• WO-Type Wolf-Rayet Stars: the Last Hurrah of Massive Star Evolution
• Upper Mass-Loss Limits and Clumping in the Intermediate and Outer Wind Regions of OB stars
• The influence of rotation on optical emission profiles of O stars
• Polarization Light Curve Modeling of Corotating Interaction Regions in the Wind of the Wolf-Rayet Star WR 6
• The nature of the companion in the Wolf-Rayet system EZ Canis Majoris
• Long uninterrupted photometric observations of the Wolf-Rayet star EZ CMa by the Toronto {\em{BRITE}} satellite reveal a very fast apsidal motion
• The Physical Parameters of Four WC-type Wolf-Rayet Stars in the Large Magellanic Cloud: Evidence of Evolution
• Using Shell Models to Investigate Clumping in the Wind of the O7Iaf+ Supergiant AzV83

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