Hydrogen and helium emission of the symbiotic binary AG Draconis during an active phase (1996–1997) ^*

Institute of Astronomy and Isaac Newton Institute of Chile Bulgarian Branch, Bulgarian National Astronomical Observatory, PO Box 136, 4700 Smolyan, Bulgaria

Corresponding author: N. Tomov, rozhen@mbox.digsys.bg

Received: 7 November 2001
Accepted: 13 March 2002

Abstract

High resolutions observations of the regions of the Hα and 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 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 4868 line contained a broad emission component indicating mainly a stellar wind from the hot secondary with a velocity of km s^-1. The mass-loss rate of this star was estimated to be about  10^-7(d/1.7 kpc) yr^-1. 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.