2002A&A...388..202T

High resolutions observations of the regions of the Hα and HeII 4868 lines of the symbiotic star AG Dra were performed during its time of activity in 1996-1997. Profiles, fluxes and radial velocity data of these lines as well as the line HeI 4713 were obtained. The Hα fluxes changed in correlation with the optical light. The emission measure of the circumbinary nebula of the system at several epochs during its 1994-1998 active phase was also calculated using Balmer continuum emission on the basis of U photometric data from the literature. It was increased by factors up to 36 above its quiescent maximal value. After the 1996 and 1997 light maxima the profile of the HeII 4868 line contained a broad emission component indicating mainly a stellar wind from the hot secondary with a velocity of 1100/1300km/s. The mass-loss rate of this star was estimated to be about 1/210^–7(d/1.7kpc)^3/2M_☉/yr. The growth of its Lyman luminosity however is not sufficient to explain the increased nebular emission during the active phase. A view that this emission could be the result of both a rise of the mass-loss rate of the cool giant of the system and a rise of the Lyman flux of the hot luminous secondary, being in a steady-state burning regime during the quiescence, is discussed.