Radio evidence on the mass loss bi-stability jump

We present the results of a first campaign of radio continuum observations toward supergiants with spectral types in the range O8 - B3. Three targets out of twelve were detected with the ATCA and the VLA. The measured fluxes and the upper limits yielded values of the stellar mass-loss rates dM/dt and the wind efficiencies. The comparison of predicted and derived values of dM/dt shows a good agreement.