A multi-frequency study of symbiotic stars – III. Simultaneous ultraviolet and optical observations of AX Persei

• Published in: Monthly notices of the Royal Astronomical Society Vol. 264; no. 4; pp. 875 - 892
• Main Authors: Ivison, R. J., Bode, M. F., Evans, A., Skopal, A., Meaburn, J.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford University Press 15.10.1993; Blackwell Science
• Subjects: Astronomy; binaries: eclipsing; Binary and multiple stars; cataclysmic variables; Earth, ocean, space; Eclipsing binaries; Exact sciences and technology; line: profiles; novae; radio continuum: stars; Stars; stars: individual: AX Per; ultraviolet: stars; Eclipsing binary stars; Line shape; Light curves; Ultraviolet spectra; Visible spectra; Symbiotic stars; Cataclysmic variable stars; Radial velocity
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/264.4.875

Spectra obtained simultaneously both at visual maximum and during eclipse with the International Ultraviolet Explorer satellite and the Isaac Newton Telescope between 1988 September and 1991 August are discussed and interpreted. Ultraviolet line ratios and phase plots are used to confirm that the C III]/Si III] emission-line ratio is subject to phase-related variations, and possible causes are discussed. Visual, photoelectric and ultraviolet light curves are used to determine the physical extent of the emission components. The resulting estimates suggest that AX Per is a detached binary system. The distance is determined bolometrically 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 outburst. Several models are discussed in an attempt to explain broad ingress/egress variations observed in the post-outburst visual light curve. The most promising of these reproduces the variations by gradually obscuring the outbursting hot component with the dusty envelope of the late-type giant. This model is shown to face difficulties when confronted by our ultraviolet observations. High-resolution spectroscopy is used to investigate the kinematics of the system. An extended, very slowly 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.