  Small-scale clumping in the winds of hot, massive stars is conventionally
included in spectral analyses by assuming optically thin clumps, a void
inter-clump medium, and a smooth velocity field. To reconcile investigations of
different diagnostics within such models, a highly clumped wind with very low
mass-loss rates needs to be invoked. Particularly, unsaturated UV resonance
lines seem to indicate rates an order of magnitude (or even more) lower than
previously accepted values. We investigate resonance line formation in
inhomogeneous hot star winds with non-monotonic velocity fields by means of 2D
stochastic and pseudo-2D radiation-hydrodynamic wind models. A Monte-Carlo
radiative transfer code is presented and used to produce synthetic line
spectra. Results: The optically thin clumping limit is only valid for very weak
lines. For intermediate strong lines, the velocity spans of the clumps are of
central importance. Current hydrodynamical models predict spans that are too
large to reproduce observed profiles unless a very low mass-loss rate is
invoked. By simulating lower spans in 2D stochastic models, the profile
strengths become drastically reduced, and are consistent with higher mass-loss
rates. To simultaneously meet the constraints from strong lines, the
inter-clump medium must be non-void. A first comparison to the observed PV
doublet in the O6 supergiant lam Cep confirms that a stochastic 2D model
reproduces observations with a mass-loss rate roughly ten times higher than
that derived from the same lines but assuming optically thin clumping.
Tentatively this may resolve discrepancies between theoretical predictions,
evolutionary constraints, and recent derived mass-loss rates, and suggests a
re-investigation of the structure predicted by current hydrodynamical models.
