  The true mass-loss rates from massive stars are important for many branches
of astrophysics. For the correct modeling of the resonance lines, which are
among the key diagnostics of stellar mass-loss, the stellar wind clumping
turned out to be very important. In order to incorporate clumping into
radiative transfer calculation, 3-D models are required. Various properties of
the clumps may have strong impact on the resonance line formation and,
therefore, on the determination of empirical mass-loss rates. We incorporate
the 3-D nature of the stellar wind clumping into radiative transfer
calculations and investigate how different model parameters influence the
resonance line formation. We develop a full 3-D Monte Carlo radiative transfer
code for inhomogeneous expanding stellar winds. The number density of clumps
follows the mass conservation. For the first time, realistic 3-D models that
describe the dense as well as the tenuous wind components are used to model the
formation of resonance lines in a clumped stellar wind. At the same time,
non-monotonic velocity fields are accounted for. The 3-D density and velocity
wind inhomogeneities show very strong impact on the resonance line formation.
The different parameters describing the clumping and the velocity field results
in different line strengths and profiles. We present a set of representative
models for various sets of model parameters and investigate how the resonance
lines are affected. Our 3-D models show that the line opacity is reduced for
larger clump separation and for more shallow velocity gradients within the
clumps. Our new model demonstrates that to obtain empirically correct mass-loss
rates from the UV resonance lines, the wind clumping and its 3-D nature must be
taken into account.
