H-ALPHA OBSERVATIONS OF EARLY-TYPE STARS

We present the results of a first session of a program run at the Catania Astrophysical Observatory to study and monitor thc H-alpha emission from early-type stars and determine the properties of their mass loss. Twelve early-type supergiants in the Cygnus region were observed repeatedly in 1988 July. From these observations we find evidence for short-term variability of the mass-loss rate, Also, a comparison with literature data reveals strong long-term variations for some of the stars. We have also developed simplified models to describe the Ha profile resulting from the combination of photospheric absorption with emission and scattering in the wind. By fitting the observed profiles with our models we determine the mass-loss rates and the velocity fields for all stars with accuracies generally better than 25%.