PROPERTIES AND VARIABILITY OF THE STELLAR WIND FROM P-CYGNI

We present the results of a study of the wind of the luminous blue variable star P Cyg. We obtained spectroscopy of P Cyg in the Her line region in the period 1988 June through 1991 July. We also used UBV photometric data to obtain information on the variations of the radius and of the effective temperature of the star, The properties of the wind of P Cyg at the different epochs of observations were determined by fitting theoretical Her profiles to the observed ones. The computation of the theoretical profiles was done using the method of Scuderi et al. (1992), enhanced to include the effect of Thomson scattering by free electrons on the Ha profile. We found that the wind velocity held displays both systematic and irregular variations which match the variability of the stellar radius and effective temperature. On the other hand, the mass-loss rate is virtually constant, at a level of(1.9 +/- 0.2) x 10(-5) M(circle dot) yr(-1), and so is the bolometric luminosity of the star. These results suggest that the mass-loss rate of P Cyg is determined entirely by internal properties of the star and is connected with its energy output whereas the wind velocity structure is also sensitive to even small changes of the photosphere conditions.