A MONTE CARLO STUDY OF FLUX RATIOS OF RAMAN SCATTERED O VI FEATURES AT 6825 AND 7082 Å IN SYMBIOTIC STARS

Symbiotic stars are regarded as wide binary systems consisting of a hot white dwarf and a mass losing giant. They exhibit unique spectral features at 6825 and 7082 angstrom, which are formed via Raman scattering of O VI lambda lambda 1032 and 1038 with atomic hydrogen. We adopt a Monte Carlo technique to generate the same number of O VI lambda 1032 and lambda 1038 line photons and compute the flux ratioF(6825)/F(7082) of these Raman scattered O VI features formed in neutral regions with a simple geometric shape as a function of H I column density N-H I. In cylindrical and spherical neutral regions with the O VI source embedded inside, the flux ratioF(6825)/F(7082) shows an overall decrease from 3 to 1 as N-H I increases in the range 10(22-24) cm(-2). In cases of slab geometry and other geometries with the O VI source outside the H I region, Rayleigh escape operates to lower the flux ratio considerably. For moderate values of N-H I similar to 10(23) cm(-2) the flux ratio behaves in a complicated way to exhibit a broad bump with a peak value of 3.5 in the case of a sphere geometry. We find that the ratio of Raman conversion efficiencies of O VI lambda lambda 1032, 1038 ranges from 0.8 to 3.5. Our high resolution spectra of " D" type HM Sge and "S" type AG. Dra obtained with the Canada-France-Hawaii Telescope show that the flux ratioF(6825)/F(7082) of AG. Dra is significantly smaller than that of HM Sge, implying that "S" type symbiotics are characterized by higher N-H I than " D" type symbiotics.