Calculated and observed UV spectra for the WN5h star R136a3. The calculated spectra represent our prototype model (model A⁺ – lowest panel), whereas the model in the upper panel (model A⁻) shows the result of our consistently calculated dynamical values based on the stellar parameter set of Crowther et al. (2010). As a consequence of the assumed compactness of the object²¹ the result of a too low mass loss rate Ṁ and a too high terminal velocity v_∞ of this model (cf. Table 12) is easily recognized by a comparison to the observed spectrum shown in the third panel²². The spectrum presented in the second panel shows clearly that a moderate reduction of the stellar mass along with an enhancement of the abundances of iron and nickel – which leads to an enhancement of Ṁ – does not solve the problem (“model A” in Table 13), because the Fe lines start to become too strong in the emission parts of the N v and C iv resonance lines²³. On the other hand, model A⁺ (lowest panel) is not affected by these weak points. Although the He ii line at 1640   Å is somewhat too weak, the spectrum is together with the dynamical parameters (cf. Table 13) in quite good agreement with the observations²⁴.