Spectroscopy of SMC Wolf-Rayet Stars Suggests that Wind-Clumping does not Depend on Ambient Metallicity

Abstract

The mass-loss rates of hot, massive, luminous stars are considered a decisive parameter in shaping the evolutionary tracks of such stars and influencing the interstellar medium on galactic scales. The small-scale structures (clumps) omnipresent in such winds may reduce empirical estimates of mass-loss rates by an evolutionarily significant factor of >=3. So far, there has been no direct observational evidence that wind-clumping may persist at the same level in environments with a low ambient metallicity, where the wind-driving opacity is reduced. Here we report the results of time-resolved spectroscopy of three presumably single Population I Wolf-Rayet stars in the Small Magellanic Cloud, where the ambient metallicity is ~1/5 Z_Sun.We detect numerous small-scale emission peaks moving outwards in the accelerating parts of the stellar winds.The general properties of the moving features, such as their velocity dispersions,emissivities and average accelerations, closely match the corresponding characteristics of small-scale inhomogeneities in the winds of Galactic Wolf-Rayet stars.

9 pages, 3 figures; accepted by ApJ Letters

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• Pre-Supernova Evolution of Massive Single and Binary Stars
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• Properties of WNh stars in the Small Magellanic Cloud: evidence for homogeneous evolution
• Direct spectroscopic observations of clumping in O-star winds
• Wolf-Rayet stars in the Small Magellanic Cloud as testbed for massive star evolution
• Global hot-star wind models for stars from Magellanic Clouds
• Observational properties of massive black hole binary progenitors
• Constraining GRB progenitor models by probing Wolf-Rayet wind geometries in the Large Magellanic Cloud
• An absence of binary companions to Wolf-Rayet stars in the Small Magellanic Cloud: implications for mass loss and black hole masses at low metallicity
• Wind properties of Milky Way and SMC massive stars: empirical Z dependence from CMFGEN models
• Spectroscopic evolution of massive stars near the main sequence at low metallicity
• Empirical mass-loss rates and clumping properties of O-type stars in the LMC