Radio observations of O-type stars

Radio observations of eight O-type giants and supergiants are reported. The observations, made at a frequency of 5 GHz with 17 antennas of the partially completed VLA, failed to detect six of the stars, and achieved possible detections of the two supergiants HD 225160 and HD 30614 at a flux density of 0.15 mJy, equal to the 3-sigma noise level. Upper limits to the mass loss rates of the undetected stars are consistent with their spectral types and luminosity classes. As for the detected stars, the mass loss rate computed for HD 30614 agrees with the average found for late O-type supergiants, while the value derived for HD 225160 is one of the highest ever measured.