A&A Supplement series, Vol. 121, January 1997, 15 - 44

Received December 27, 1995; accepted April 20, 1996

Raman scattering in symbiotic stars. II. Numerical models

T.J. Harries - I.D. Howarth

Send offprint request: Tim Harries (tjh@st-and.ac.uk)

  School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, Scotland
  Dept. of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

Abstract:

We present numerical models of Raman-line formation in symbiotic systems, based on Monte-Carlo simulations of scattering of OVI resonance-line photons from a hot source in the extended, expanding atmosphere of a cool companion, and we explore the sensitivity of the model results to the input parameters. The model successfully reproduces the observed line ratios, velocities, and polarizations, and the viewing-angle (orbital) dependence of the line strengths and polarized intensities. In principle, the position-angle dependence of the polarization in resolved Raman lines provides a diagnostic of the extent of the ionized region in symbiotic systems; however, axisymmetric geometries with `up-down' symmetry, such as we use, fail to reproduce the most commonly observed dependence of PA on velocity. Raman-line polarization morphology is shown to be a powerful probe of the conditions in the red-giant wind; this is particularly true if observations are available at different orbital phases, so that geometrical and physical variables may more easily be isolated.

keywords: stars: binaries: symbiotic -- stars: mass-loss -- polarization

 
• 1. Introduction
• 2. Model formulation
• 3. Implementation
• 4. A reference model
• 5. Reference-model results
• 6. Variants on the reference model
• 7. Sensitivity to viewing angle
• 8. Sensitivity to mass-loss rate
• 9. Sensitivity to velocities
• 10. Sensitivity to absorption opacities
• 11. Sensitivity to photon-source extension
• 12. Discussion
• References