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 (12)

• 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
• Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates
• Unlocking Galactic Wolf-Rayet stars with $\text{Gaia}$ DR2 I: Distances and absolute magnitudes
• 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
• On the Importance of the Interclump Medium for Superionization: O VI Formation in the Wind of Zeta Pup
• Tides in asynchronous binary systems
• WO-Type Wolf-Rayet Stars: the Last Hurrah of Massive Star Evolution
• 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
• Using Shell Models to Investigate Clumping in the Wind of the O7Iaf+ Supergiant AzV83

Cited by in corpus (5)

• The morphing of decay powered to interaction powered Type II supernova ejecta at nebular times
• The PLATO field selection process. II. Characterization of LOPS2, the first long-pointing field
• X-Shooting ULLYSES: massive stars at low metallicity: XII. The clumped winds of O-type (super)giants in the Large Magellanic Cloud
• Radiative-transfer models for dusty Type II supernovae
• Constraints on Clumps in the Representative Wind of the WN8 Wolf-Rayet star HD96548 = WR40 with Simultaneous Broadband Light and Linear-Polarisation Variability