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Tim Harries
Symbiotic binaries

Introduction

A symbiotic binary consists of a mass-losing red giant star and a hot, compact companion (typically a white-dwarf). The hot star ionizes some of the material shed by the giant, and this leads to the symbiotic's characterisitic composite spectrum of nebular emission lines superimposed on molecular absorption bands. Symbiotic binaries are valuable laboratories for the study of cool stellar winds, ionized nebulae, wind-fed accretion processes and wind-wind collision dynamics.

Raman-scattering

A strong OVI resonance doublet (1032, 1038 angstroms) is produced in the vicinity of the white-dwarf star and is Raman-scattered by neutral hydrogen in the red giant's wind. This results in Raman-scattered emission lines at 6830 and 7088 angstroms. Since the Raman-scattering is dipolar and the scattering geometry is asymmetric (with scattering region essentially illuminated by a point source), the Raman-lines are highly linearly polarized. By measuring the orbital phase dependence of the Raman-line polarization we are able to determine the orbits of these long-period systems. This represents the only method for finding orbits of the longest (many decades) period systems, since the orbital Doppler shifts in these binaries will be substantially less than the pulsation speed of the Mira. In addition to orbital information, the Raman-lines encode both geometrical and dynamical information on the red giant wind. For the best studied systems it will be possible construct tailored models in order to measure the distribution of the neutral material, the mass-loss rates, and the velocity laws of the red giant wind.

The image to the left is a link to a movie of a simulation of Raman-scattering in a symbiotic binary. The panels are (clockwise, from top left) the intensity image, the intensity image + polarization vectors, the velocity image, and the polarized intensity.

See also Tim Harries' publication list and the Group publications list .

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