have chosen the following stellar parameters for our WC model:  = 40000 K, and  = 5.36. The adopted mass is $M$ = 10 , again based on the compilation of Nugis & Lamers (2000) for late WC stars, and in line with the expectation that a later evolutionary phase results in a smaller mass, as a result of mass loss. The terminal wind velocity we adopt is  = 1200 [km s$^{-1}$]{}, as found by Dessart et al. (2000) for the WC8 star WR135. Nugis & Lamers (2000) found $N_{\rm C}/N_{\rm O}$ $\simeq$ 5 for all WC subtypes, but a $N_{\rm C}/N_{\rm He}$ that is spectral-type dependent, ranging between 0.18 – 0.36. These abundance ratios are by number. Based on the above, it is clear that oxygen is not expected to be an important line driver, however carbon should become crucial at very low iron abundance. We adopt a ratio $N_{\rm C}/N_{\rm He}$ of 1/3, which corresponds to an equal mass contribution of these two elements. Such a high ratio maximizes the potential effect of carbon line driving, compared to that of Fe. (If we would take a lower ratio, carbon would start to dominate at a lower $Z$ value.)

Note 