2005A&A...430L..41P

We present empirically determined ionization conditions for the winds of 106 luminous B0 to B5 stars observed by IUE. The UV wind lines are modelled to extract products of mass-loss rates times ionization fractions ({dot}(M)q_i(w), where w=v/v_∞) for NV, CIV, SiIV, SiIII, AlIII and CII. We describe the general behaviour of the {dot}(M)q_i(w) and their ratios, demonstrating that the wind ionization increases with distance from the star, contrary to recent findings for O star winds. Using empirical mass-loss rates (from Hα observations) and model prescriptions, we derive mean q_i(w) values integrated over the wind, <q_i>. These <q_i> are quite small, never exceeding 15% for AlIII or 2% for SiIV. This is surprising, since the <q_i> for these ions clearly peak within the observed spectral range. We conclude that the low <q_i> arise because the <{dot}(M)q_i> are underestimated by the wind models, which assume that the outflows are smooth when they are, in fact, highly structured.