IUE observations of the symbiotic star AG Draconis

Abstract

The extensive IUE observations of the symbiotic system AG Draconis along seventeen years have allowed the coverage of long periods of quiescence and of a number of different outbursts. This presents an unique opportunity to study the nature of the hot star as well as the physics of the accretion processes. The IUE data cover eleven orbital cycles of the system, and show that UV variations during quiescence are characterized by the modulation of the continuum and the emission lines along the 554 days orbital motion. During the IUE lifetime six outbursts were observed. These outbursts can be divided in two types according to its "hardness", as derived from the behaviour of the UV continuum and emission lines. Simultaneous X-ray observations with EXOSAT and ROSAT point to a clear anticorrelation of optical/UV and X-ray fluxes during outburst.