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| Paper: |
The Observed Metallicity Dependence of the Mass Loss of O and Early-B Stars |
| Volume: |
353, Stellar Evolution at Low Metallicity: Mass Loss, Explosions, Cosmology |
| Page: |
99 |
| Authors: |
de Koter, A. |
| Abstract: |
We review the observational evidence for a dependence of the mass loss through stellar winds of hot massive stars on the metal content of their atmospheres. The metal content of stars in the Small Magellanic Cloud is discussed, and an overview is given of state-of-the-art dM/dt determinations of OB stars in SMC and the Milky-Way. Assuming a powerlaw dependence of mass loss on metal content, dM/dt ∝ Zm, and adopting the theoretical result v∞ ∝ Z0.13 (Leitherer et al. 1992) for the relation between wind terminal flow velocity and metal content, we find from an analysis of the wind momentum luminosity relation (WLR) that m = 0.67 ± 0.22 for stars more luminous than 105.25LSolar. This compares very well with the prediction m = 0.69 ± 0.10 by Vink et al. (2001). For stars of lower luminosity the winds are so weak that their strengths can no longer be derived from Hα fitting and one must rely on the analysis of ultraviolet lines. In this regime the observed WLR appears much steeper than expected from theory, leading to an overprediction of the wind strength by up to a factor 100. We discuss possible explanations. UV analyses also suggests that about half of the stars brighter than ∼ 105.15 have clumped winds, implying that their wind strengths may be overestimated by factors 3 to 10. This would imply that also strong winds are overpredicted by current wind theory. |
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