FUSE Spectroscopy of the Accreting Hot Components in Symbiotic Variables

Prior research has shown that symbiotic variable stars host interacting binary systems with hot and cool components. However, the exact nature of the hot components—whether white dwarfs, accretion disks, or boundary layers—remains unclear in many cases. While optical and ultraviolet spectroscopy have provided insights, the Lyman Limit region remains underexplored. This gap motivated the use of FUSE spectroscopy to probe shorter wavelengths. No prior work had resolved the physical properties of hot components in quiescent symbiotic systems using extended ultraviolet data. The lack of detailed temperature and gravity measurements for these hot components in quiescence limits our understanding of accretion processes. This paper's contribution is to analyze FUSE spectra of four quiescent systems, comparing them with NLTE and accretion disk models. The study aims to clarify the structure and temperature of hot components in systems with and without outburst histories. This approach provides a new observational window to constrain the nature of the accreting objects.

The aim of this study is to determine the physical properties of hot components in quiescent symbiotic systems using FUSE spectroscopy. The specific problem addressed is the lack of detailed temperature and gravity data for these components in the Lyman Limit region. The motivation stems from the need to distinguish between white dwarf photospheres and accretion disk models in systems with and without outburst histories. By analyzing four quiescent systems, the researchers aim to reveal whether the hot components are low-mass white dwarfs, boundary layers, or other structures. The study focuses on systems with and without recorded outbursts to compare their hot component properties. The use of FUSE spectra allows for extended wavelength coverage down to the Lyman Limit. This approach helps to probe the shortest wavelengths, where the hot component's emission is most prominent. The goal is to improve our understanding of accretion processes in symbiotic binaries.

The researchers used FUSE archival spectra to analyze four symbiotic variables in quiescence. They extended the wavelength coverage down to the Lyman Limit to capture the shortest wavelength emission from hot components. The study compared observed spectra with NLTE model white dwarf photospheres and optically thick accretion disk models. They examined systems with and without outburst histories to identify differences in hot component properties. The analysis focused on the far ultraviolet region, which is sensitive to high-temperature sources. The researchers considered the possibility of a triple system in CQ Dra, where a red giant transfers matter to a cataclysmic variable. They evaluated the size and temperature of the hot component contributing to the shortest wavelengths in FUSE spectra. The study used surface temperature and gravity measurements to classify the hot components as low-mass white dwarfs or boundary layers.

The analysis revealed that RW Hya's hot component is a low-mass white dwarf with a surface temperature of 160,000K. In CQ Dra, the hot component is consistent with a boundary layer with a surface temperature of ∼120,000K and a size of ∼4% of the white dwarf surface. EG And's hot component is a hot, bare, low-mass white dwarf with a surface temperature of 80-95,000K and a surface gravity of log(g) = 7.5. AE Ara's hot component is a low-gravity (log(g) ∼ 6) white dwarf with a surface temperature of ∼130,000K. The researchers found that the hot components in these systems are not consistent with high-mass white dwarfs or optically thin accretion disks. The FUSE spectra provided evidence for boundary layers in systems with outburst histories. The study confirmed that the hot components in quiescent systems are low-temperature white dwarfs or boundary layers. These results help distinguish between different accretion models in symbiotic binaries.

The authors conclude that the hot components in quiescent symbiotic systems are low-mass white dwarfs or boundary layers. Their findings suggest that the hot component in RW Hya is a low-mass white dwarf with a surface temperature of 160,000K. In CQ Dra, the hot component is consistent with a boundary layer with a surface temperature of ∼120,000K. The study found that the hot components in EG And and AE Ara are low-mass white dwarfs with surface temperatures of 80-95,000K and ∼130,000K, respectively. The researchers propose that the hot components in these systems are not high-mass white dwarfs or optically thin accretion disks. The FUSE spectra provided evidence for boundary layers in systems with outburst histories. The study supports the use of extended ultraviolet data to probe the shortest wavelength emission from hot components. These results contribute to our understanding of accretion processes in symbiotic binaries.