al. 2001), therefore these elements become “less passive”. At $Z = 1/300 {\mbox{$Z_{\odot}$}}$ this contribution may amount to several tens of percents ($\sim$ 10–30 %). Second, and especially relevant for WC stars, the mass fraction contained in “passive ions” decreases with an increasing surface abundance of carbon and oxygen. For the WC model that we study here, already half of the mass in contained in carbon. Therefore, if ion-decoupling would occur, one may expect that the predictions presented in this paper overpredict  by at most a factor of two.

The WR parameters {#s_parameters}
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This study is not intended to be a full parameter study of WR stars, but is deliberately limited to very specific choices of stellar properties. For an accurate modelling of higher temperatures, i.e. earlier spectral types, the line list is required to be complete for the higher ionization stages. As we are principally interested in the metallicity dependence, we choose to model “late” WR stars of both flavours: WNL, the late-type nitrogen-rich stars, and WCL, the late-type carbon-rich ones. Our strategy is as follows: we choose typical WN/WC stellar parameters such as luminosity and effective temperature, based on studies using the most sophisticated “standard” WR star 