FUSE Spectroscopy of the Accreting Hot Components in Symbiotic Variables

We have conducted a spectroscopic analysis of the far-ultraviolet archival spectra of four symbiotic variables, EG And, AE Ara, CQ Dra, and RW Hya. RW Hya and EG And have never had a recorded outburst, while CQ Dra and AE Ara have outburst histories. We analyze these systems while they are in quiescence in order to help reveal the physical properties of their hot components via comparisons of the observations with optically thick accretion disk models and non-LTE model white dwarf photospheres. We have extended the wavelength coverage down to the Lyman limit with Far Ultraviolet Spectroscopic Explorer (FUSE) spectra. We find that the hot component in RW Hya is a low-mass white dwarf with a surface temperature of 160,000 K. We reexamine whether or not the symbiotic system CQ Dra is a triple system with a red giant transferring matter to a hot component made up of a cataclysmic variable in which the white dwarf has a surface temperature as low as ∼20,000 K. The very small size of the hot component contributing to the shortest wavelengths of the FUSE spectrum of CQ Dra agrees with an optically thick and geometrically thin (∼4% of the WD surface) hot (∼120,000 K) boundary layer. Our analysis of EG And reveals that its hot component is a hot, bare, low-mass white dwarf with a surface temperature of 80,000-95,000 K, with a surface gravity {log}(g)=7.5. For AE Ara, we also find that a low-gravity ({log}(g)∼ 6), hot (T∼ {{130,000}} K) WD accounts for the hot component.