Hot, massive stars possess line-driven winds. The mass-loss rates involved are, however, highly uncertain and strongly depend on whether the winds are smooth or develop clumpy structures caused by instabilities. Furthermore, deviation from spherical symmetry can occur due to stellar rotation.

We studied the influence of non-spherical mass loss and stellar rotation on the wind geometry.

Ionization structure in the winds of B[e] supergiants - Kraus & Lamers 2003, A&A, 405, 165 & Kraus 2006, A&A, 456, 151

Furthermore, the influence of clumping on the continuum energy distribution of a sample of OB supergiant stars has been investigated:

Kraus, Kubát, & Krtička, 2008, 481, 499

Kraus, Kubát, & Krtička, 2008, in Clumping in Hot star Winds, p. 51

Kraus, Borges Fernandes, Kubát, 2009, A&A 499, 291