Mass loss rate determination of southern OB stars

A sample of OB stars (eleven Of, one O and one B supergiant) has been surve yed with the Australia Telescope Compact Array at 4.8 and 8.64 GHz with a r esolution of similar to2"-4". Five stars were detected; three of them have negative spectral indices, consistent with non-thermal emission, and two ha ve positive indices. The thermal radiation from HD 150135 and HD 163181 can be explained as coming from an optically thick ionized stellar wind. The n on-thermal radiation from CD-47 degrees 4551, HD 124314 and HD 150136 possi bly comes from strong shocks in the wind itself and/or in the wind collidin g region if the stars have a massive early-type companion. The percentage o f non-thermal emitters among detected O stars has increased up to similar t o 50%. The Of star HD 124314 clearly shows flux density variations. Mass lo ss rates (or upper limits) were derived for all the observed stars and the results compared with non-radio measurements and theoretical predictions.