A MULTIFREQUENCY STUDY OF SYMBIOTIC STARS .3. SIMULTANEOUS ULTRAVIOLET AND OPTICAL OBSERVATIONS OF AX PERSEI

Spectra obtained simultaneously both at visual maximum and during ecli pse with the International Ultraviolet Explorer satellite and the Isaa c Newton Telescope between 1988 September and 1991 August are discusse d and interpreted. Ultraviolet line ratios and phase plots are used to confirm that the C III]/Si III] emission-line ratio is subject to pha se-related variations, and possible causes are discussed. Visual, phot oelectric and ultraviolet light curves are used to determine the physi cal extent of the emission components. The resulting estimates suggest that AX Per is a detached binary system. The distance is determined b olometrically and by spectroscopic parallax. Deep visual minima, which reach below the lowest quiescent level, are thought to reflect total eclipses of the source of optical continuum which must shrink in outbu rst. Several models are discussed in an attempt to explain broad ingre ss/egress variations observed in the post-outburst visual light curve. The most promising of these reproduces the variations by gradually ob scuring the outbursting hot component with the dusty envelope of the l ate-type giant. This model is shown to face difficulties when confront ed by our ultraviolet observations. High-resolution spectroscopy is us ed to investigate the kinematics of the system. An extended, very slow ly expanding region is indicated by the radial velocities of hydrogen absorption lines in the Balmer series. Finally, the revised positional coordinates given here have led to the first detection of this system at radio wavelengths.