A COMPARISON BETWEEN OBSERVED AND PREDICTED MASS-LOSS RATES AND WIND MOMENTUM OF O-STARS

Empirical mass-loss rates were derived for 28 luminous O stars from ra dio fluxes and Ha equivalent widths. Comparison with theoretical value s predicted by the theory of radiatively driven winds reveals a discre pancy of 0.30 +/- 0.05 dex, with the theoretical values being too low. We show that there is not only a mass-loss discrepancy but also a mom entum flux discrepancy. The theoretically predicted momentum fluxes ar e too low by 0.17 +/- 0.04 dex. This discrepancy is independent of the adopted stellar mass. We demonstrate that the momentum discrepancy in the most luminous O stars is comparable to the one found in the least extreme Wolf-Rayet stars. We suggest that the physical reason for the break-down of the theory in Wolf-Rayet stars and the most luminous O stars may be related.