1998A&A...332..251S

Fifteen O and B supergiants have been observed with the Very Large Array (VLA) at 4.85, 8.45, and 14.95GHz in order to make a detailed comparative study of the mass loss rates evaluated from Hα and radio continuum observations and reveal and quantify possible departures from standard wind conditions. We detected 12 sources, 7 of which for the first time, thus increasing by 30% the total number of detections of OB supergiants in the northern sky. Radio spectral slopes indicate that the radio emission is mainly of thermal origin in all objects with one exception (HD 190603) out of the 12 detections. Our results demonstrate the value of using Hα for mass loss rate determinations, especially for stars that are too distant or too faint to be detected with radio techniques. The relationship {dot}(M)-L for supergiants turns out to be appreciably flatter than commonly reported, i.e. log{dot}(M)=(1.25±0.30)logL.