Mass loss rates in central stars of planetary nebulae.

Central stars of planetary nebulae frequently exhibit fast winds. They may be important for the structure of the whole nebula as well as for the evolution of the central star. Their speed is typically two orders of magnitude higher than that of the classical optically visible nebula, which in turn expands a few times faster than the most external winds detected in few cases in the radio domain. The author reviews the status of art in the determination of the mass loss rates (M˙) associated with these fast winds.