Properties of WNh stars in the Small Magellanic Cloud: evidence for homogeneous evolution

Abstract

We derive the physical properties of three WNh stars in the SMC to constrain stellar evolution beyond the main sequence at low metallicity and to investigate the metallicity dependence of the clumping properties of massive stars. We compute atmosphere models to derive the stellar and wind properties of the three WNh targets. A FUV/UV/optical/near-infrared analysis gives access to temperatures, luminosities, mass loss rates, terminal velocities and stellar abundances. All stars still have a large hydrogen mass fraction in their atmosphere, and show clear signs of CNO processing in their surface abundances. One of the targets can be accounted for by normal stellar evolution. It is a star with initial mass around 40-50 Msun in, or close to, the core He burning phase. The other two objects must follow a peculiar evolution, governed by fast rotation. In particular, one object is likely evolving homogeneously due to its position blue-ward of the main sequence and its high H mass fraction. The clumping factor of one star is found to be 0.15+/-0.05. This is comparable to values found for Galactic Wolf-Rayet stars, indicating that within the uncertainties, the clumping factor does not seem to depend on metallicity.

16 pages. A&A accepted

References in corpus (9)

• The Supernova -- Gamma-Ray Burst Connection
• The empirical metallicity dependence of the mass-loss rate of O- and early B-type stars
• Mass loss from late-type WN stars and its Z-dependence: very massive stars approaching the Eddington limit
• The most massive stars in the Arches cluster
• Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates
• The VLT-FLAMES survey of massive stars: atmospheric parameters and rotational velocity distributions for B-type stars in the Magellanic Clouds
• The VLT-FLAMES survey of massive stars: Wind properties and evolution of hot massive stars in the LMC
• A Spectroscopic Survey of WNL Stars in the LMC: General Properties and Binary Status
• The very massive binary NGC3603-A1