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 A, which are formed via Raman scattering of O vi λλ 1032 and 1038 with atomic hydrogen. We adopt a Monte Carlo technique to generate the same number of O vi λ1032 and λ1038 line photons and compute the flux ratio 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 ratio shows an overall decrease from 3 to 1 as N H i increases in the range . 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 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 λλ 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 ratio 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.