A wind analysis of an evolved giant -- phase-resolved FUSE and HST/STIS observations of an eclipsing symbiotic binary
Cian Crowley (Trinity College, Dublin)
Brian Espey (Trinity College, Dublin)
Steve McCandliss (Johns Hopkins University, Baltimore, MD)
A major outstanding problem in stellar astrophysics lies in understanding the
wind generation mechanism by which evolved giants lose mass. Phase-resolved
observations of eclipsing symbiotic binary systems, containing a mass-losing
giant and a hot white dwarf, are ideal for studying the wind generation
mechanisms in evolved stars. For such systems it is possible to use the orbital
motion of the dwarf through the giant's wind to provide a pencil-beam view
through the circumstellar gas. FUV observations can probe different layers of
the wind in absorption, permitting the derivation of the velocity profile and
providing valuable, spatially-resolved diagnostics of the cool wind.
We present a series of new FUSE and HST/STIS observations of two such systems
and discuss our findings. The velocity profiles, and by implication, wind
generation mechanisms for these giants are found to differ from those predicted
by commonly used parametrisations. The phasing of our observations allow us to
examine the density, temperature and velocity structure in the wind acceleration
region, as well as the composition of the outflowing material.