clumps. The interclump medium is assumed to be void. Typical values for the clumping factor in WR winds are found to be 0.1 – 0.25 (Hillier & Miller 1999, Hamann & Koesterke 1998). The ionization structure of a clumped wind will behave similarly to that of an unclumped wind with an $\sqrt{f}$ times lower mass-loss rate. There may be a dependence of the clumping factor on metallicity. If it holds true that weaker winds (e.g. O star winds) are less clumped than WR winds (e.g. Lamers & Leitherer 1993, but see Bouret et al. 2005), one might speculate that the winds of WR stars at lower $Z$ may also be less clumped than those of Galactic WR stars.

Nevertheless, we emphasize that the neglect of clumping could effect the results presented in this paper.

Ion decoupling
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In line-driven winds, the ions that are most effective in absorbing photons (i.e. those with many lines in the region of the flux maximum of the star; notably C, N, O, and Fe) redistribute the momentum they have gained – through friction – to ions that are only marginally effective line absorbers. These latter more “passive ions” include H and He, containing most 