6 Conclusions

We computed non-isothermal three-component models of OB star winds with allowing for different temperatures of each component and with inclusion of the Gayley-Owocki (GO) heating/cooling. We showed that temperature differentiation takes place in the winds of B stars starting from spectral type B3. The temperature of absorbing ions is of the order $10^3\,{\rm K}$higher than temperature of other components whereas the temperatures of passive plasma and electrons is nearly equal. The main sources which trigger the temperature differentiation are GO, frictional, and radiative heating.

Another important effect studied in this paper is the GO heating and cooling, which is important mainly for the low density winds. We showed that this effect is a direct consequence of the dependence of the radiative force on the wind velocity. We derived the GO heating formula directly from the Boltzmann equation. More subtle GO cooling operates near the star at the wind base whereas the GO heating affects the flow mainly in outer parts of the wind. These effects become important starting from stellar type O6. Frictional and GO heating provides a possibility for an alternative explanation of UV-excess observed in some B stars.

At the lowest densities either the passive component falls back onto the star or purely metallic wind exists. If the reaccretion takes place then ionic components is frictionally heated to the temperatures of orders millions K creating corona-like region. This effect can explain enhanced X-ray activity in many of B stars.

Finally, we compared our computed terminal velocities with those derived from observation. There is quite good agreement between them. The systematic difference between observed and predicted (by a "cooking formula'' of KPPA) terminal velocities found by LSL was removed. However, we found no effects of frictional or GO heating in our sample.

Acknowledgements

The authors would like to thank Dr. John Porter for pointing their attention to the importance of the effect of Gayley-Owocki (Doppler) heating, Dr. Kenneth Gayley and Prof. Michal Lenc for their comments on the manuscript of this paper. This research has made use of NASA's Astrophysics Data System Abstract Service (Kurtz et al. 2000; Eichhorn et al. 2000; Accomazzi et al. 2000; Grant et al. 2000). This work was supported by a grant GA CR 205/01/0656 and by projects K2043105 and Z1003909.