EG and: Far ultraviolet spectroscopic explorer and Hubble space telescope STIS monitoring of an eclipsing symbiotic binary

Abstract

We present highlights and an overview of 20 FUSE and HST STIS observations of the bright symbiotic binary EG And. The main motivation behind this work is to obtain spatially resolved information on an evolved giant star in order to understand the mass-loss processes at work in these objects. The system consists of a low-luminosity white dwarf and a mass-losing, nondusty M2 giant. The ultraviolet observations follow the white dwarf continuum through periodic gradual occultations by the wind and chromosphere of the giant, providing a unique diagnosis of the circumstellar gas in absorption. Unocculted spectra display high-ionization features, such as the O vi resonance doublet, which is present as a variable (hourly timescales), broad wind profile, which diagnose the hot gas close to the dwarf component. Spectra observed at stages of partial occultation display a host of low-ionization, narrow absorption lines,with transitions observed fromlower energy levels up to 5 eVabove ground. This absorption is due to chromospheric/wind material, with most lines due to transitions of Si ii, P ii, N i, Fe ii, andNi ii, as well as heavily damped H i Lyman series features.Nomolecular features are observed in the wind acceleration region despite the sensitivity of FUSE toH2. From analysis of the ultraviolet data set, as well as optical data, we find that the dwarf radiation does not dominate the wind acceleration region of the giant and that observed thermal and dynamic wind properties are most likely representative of isolated red giants.