Clumping in the Winds of Wolf-Rayet Stars

Abstract

We attempt to determine the driver for clumping in hot-star winds by extending the measure of the spectral variability level of Galactic Wolf-Rayet stars to by far the hottest known among them, the WN2 star WR 2 and the WO2 stars WR 102 and WR 142. These three stars have T* = 140 kK and 200 kK, the last two being well above the bulk of WR stars with T* ~ 40-120 kK. This full temperature range for WR stars is much broader than that of their O-star progenitors (~30-50 kK), so is better suited to look for any temperature dependence of wind clumping. We have obtained multiple observations with high signal-to-noise, moderate-resolution spectroscopy in search of smallscale variability in the strong emission lines from the dense winds of these three extreme stars, and find a very low-level of variability in both stars. Temperature and terminal velocity are correlated, so faster winds show a lower variability, though this trend goes against any predictions made involving Line Deshadowing Instability (LDI) only, implying that instabilities intrinsic to LDI are not the main source of wind clumping. Instead, it could be taken as support for the suggestion that clumps are caused by a sub-surface convection zone (SSCZ) at T ~ 170 kK, since such an SSCZ would have little opportunity to operate under the hydrostatic surface of these hottest WR stars. It is still possible, however, that an SSCZ-related driver could interact with nonlinear line instability effects to enhance or possibly even produce clumps.

17 pages, 6 figures, 5 tables, ApJ, in press

References in corpus (4)

• 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
• Direct spectroscopic observations of clumping in O-star winds
• Investigating the origin of the spectral line profiles of the Hot Wolf-Rayet Star WR2

Cited by in corpus (8)

• First 3D Radiation-Hydrodynamic Simulations of Wolf-Rayet Winds
• A spectroscopic multiplicity survey of Galactic Wolf-Rayet stars. III. The northern late-type nitrogen-rich sample
• Space Photometry with BRITE-Constellation
• Strong nebular HeII emission induced by He${}^{+}$ ionizing photons escaping through the clumpy winds of massive stars
• Particle acceleration and magnetic field amplification by relativistic shocks in inhomogeneous media
• Constraints on Clumps in the Representative Wind of the WN8 Wolf-Rayet star HD96548 = WR40 with Simultaneous Broadband Light and Linear-Polarisation Variability
• Property of downstream turbulence driven by the special relativistic shock-clump interaction
• ALMA measurements of mass loss and wind clumping in the massive stars of the Arches cluster