Probing the Accreting Hot Components in Six S-Type Symbiotic Variables

TL;DR

This study analyzes ultraviolet spectra of six symbiotic star systems during quiescence to understand their hot components, revealing a low-mass white dwarf in RW Hya and a triple system in CQ Dra with a white dwarf around 50,000K.

Contribution

It provides detailed spectroscopic modeling of six symbiotic systems' hot components, including the first characterization of RW Hya's white dwarf and the identification of CQ Dra as a triple system.

Findings

RW Hya hosts a 160,000K white dwarf.

CQ Dra is a triple system with a 50,000K white dwarf.

Spectroscopic analysis clarifies hot component nature in symbiotic systems.

Abstract

We have carried out a spectroscopic analysis of the far ultraviolet spectra of six symbiotic variables. Two systems, LT Del, which has had one recorded outburst, and BD-21 3873 (= IV Vir) which has had no recorded outburst, are yellow symbiotic systems. Two other systems, V443 Her and RW Hya, have also never had a recorded outburst. Two other symbiotics, StHa190 and CQ Dra, are more strongly interacting with an outburst history. We have studied these systems during their quiescence in order to shed light on the nature of their hot components by fitting their archival far ultraviolet spectra with optically thick accretion disk models and NLTE model white dwarf photospheres. Using the critical advantage offered by extending wavelength coverage down to the Lyman Limit with FUSE spectra, we find that the hot component in RW Hya is a low mass white dwarf with a surface temperature of 160,000K while 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 whose white dwarf has a surface temperature of $\sim$50,000K. Implications are discussed.