P V and the Mass Loss Discrepancy in O Stars
  Building upon a previous analysis of P V wind lines in LMC O stars, we analyze the P V wind lines in a sample of Galactic O stars which have empirical mass loss rates determined from either their radio fluxes or H alpha profiles. Since the wind analysis provides a measure of \dot{M}q where q is the ionization fraction of the ion, we determine q(P V) observationally. In spite of model predictions that q should be about 1 for mid-O stars, we find q(P V) is less than 0.15 throughout the O stars. We discuss the origin of this discrepancy. 
D. Massa, A.W. Fullerton & R.K. Prinja