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Session 60 - Multiple Stars.
Display session, Wednesday, June 12
Symbiotic binary stars generally consist of a hot, compact star in orbit around a cooler red giant. A subset of these objects undergoes eclipses due to the plane of the binary orbit being close to our line of sight. For this subset, there are phases at which the large, cool giant interposes itself between us and the hot white dwarf. We will present results for two symbiotic binaries that have been observed in the far-ultraviolet during these phases. Both objects show unmistakable evidence for the presence of atomic and molecular hydrogen absorption in their spectra related to the extended red giant atmosphere, or perhaps the shocked region between the two stars where their winds interact.
AG Peg was observed during eclipse by the far-ultraviolet detector of the Berkeley spectrometer during the Orfeus space astronomy mission in September 1993. Initial results suggest that the absorption lines are broader than the detector resolution, with a linewidth similar to that of the shocked gas in this system.
EG And was observed twice with the Hopkins Ultraviolet Telescope (HUT) during the recent Astro-2 space shuttle mission in March 1995. The spectrum of this object is grossly similar to that of AG Peg, albeit at lower resolution. The spacing of the two observations provides us with two lines of sight through the extended atmosphere of the giant star. We will show our fits to these spectra and discuss the implications for models of these binaries, particularly in the light of other diagnostics of these systems. In addition, we will discuss the possible presence of emission lines which are visible in the absorption-corrected spectra of these objects. Our results show the utility of far-ultraviolet observations for probing the cooler material in these systems, as well as the hottest emission line emitting gas.
This work was funded by NASA grant NAS 5-27000 to the Johns Hopkins University and by NAG 8-1049 to the University of Pittsburgh.
Program listing for Wednesday