According to previous investigations the effect of diffusion in the stellar atmospheres and envelopes of subdwarf B ( sdB ) stars with luminosities 10 \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ < $ } } } L% / L _ { \odot } \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox% { $ < $ } } } 100 strongly depends on the presence of weak winds with mass loss rates \dot { M } \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ < % $ } } } 10 ^ { -12 } M _ { \odot } / yr .
These calculations with the mass loss rate as a free parameter have shown that it is hardly possible to reproduce the measured abundances of helium and metals simultaneously .
A possible reason is the decoupling of metals , which preferably absorb the photon momentum , from hydrogen and helium in the wind region .
In the present paper it will be investigated if “ chemically homogeneous ” winds , as assumed in previous investigations , with mass loss rates \dot { M } \leq 10 ^ { -12 } M _ { \odot } / yr can exist .
From an observational point of view the existence of weak winds in sdB stars is unclear .
Only in the most luminous ones possible wind signatures have been detected .
Therefore it will be investigated if according to the theory of radiatively driven winds the existence of weak winds is plausible .
A stellar mass M _ { * } = 0.5 M _ { \odot } is assumed .

The results for effective temperatures T _ { eff } = 35000 , 30000 and 25000 K , metallicities 0.1 \leq Z / Z _ { \odot } \leq 1 predict decreasing mass loss rates with increasing surface gravity .
Dependent on the luminosity and metallicity the mass loss rates are between about 10 ^ { -11 } M _ { \odot } / yr and zero .
If at all , chemically homogeneous winds can exist for the most luminous sdB stars only .
For the other ones selective winds are expected which should lead to additional changes of the surface composition .

In sdB stars , hot white dwarfs and HgMn stars ( which are chemically peculiar main sequence stars ) the measured metal abundances are tendencially lower than the ones predicted from diffusion calculations which assume an equilibrium between gravitational settling and radiative levitation .
Only for helium in almost all cases the measured abundances are larger than the predicted ones , but usually lower , below the solar value .
This may be an indication that the abundance anomalies of metals are preferably due to the selective winds , whereas the helium deficiencies are due to gravitational settling , which for still unknown reasons is less effective than expected in an undisturbed stellar atmosphere .