Illumination in Symbiotic Binary Stars: Non-LTE Photoionization Models. II. WIND Case

Abstract

We describe a non-LTE photoionization code to calculate the wind structure and emergent spectrum of a red giant wind illuminated by the hot component of a symbiotic binary system. We consider spherically symmetric winds with several different velocity and temperature laws and derive predicted line fluxes as a function of the red giant mass-loss rate, Ṁ. Our models generally match observations of the symbiotic stars EG And and AG Peg for Ṁ~10^-8 to 10^-7 M_⊙ yr^-1. The optically thick cross section of the red giant wind as viewed from the hot component is a crucial parameter in these models. Winds with cross sections of 2-3 red giant radii reproduce the observed fluxes because the wind density is then high: ~10⁹ cm^-3. Our models favor winds with acceleration regions that either lie far from the red giant photosphere or extend for 2-3 red giant radii.