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

3-D radiative transfer in clumped hot star winds I. Influence of clumping on the resonance line formation