1999A&A...347..151T

High and intermediate resolution observations of the blue and the Hα spectral regions of the symbiotic star AG Dra at quiescence and during an active phase in 1994 and 1995 were performed. Variations of profiles, fluxes and radial velocity data of a number of emission lines are investigated. The width (FWHM) of all of these lines was very large at times close to the 1994 light maximum. The emission measure of the surrounding nebula was also calculated using Balmer continuum emission on the basis of U photometric observations from the literature. It turned out that at the times of the 1994 and 1995 visual light maxima the emission measure has increased by a factor of 15 and 8 respectively, compared with its quiescent maximal value. After the 1995 light maximum the profiles of the Hβ and Hγ lines contained a broad emission component that indicated a hot stellar wind. The velocity of this wind and the mass-loss rate of the hot secondary giving its rise, were equal to 800km/s and 2x10^–7M_☉/yr. A view that the observed presence of a hot wind and the increase of the emission measure together can be considered as an argument in support of the thermonuclear outburst model is discussed. Moreover, we argue that a shocked wind region with X-ray luminosity of about 10L_☉ must be present in this system when the hot wind exists.