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 Å and 7082 Å , 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 ratio F ( 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 _ { HI } .
In cylindrical and spherical neutral regions with the O vi source embedded inside , the flux ratio F ( 6825 ) / F ( 7082 ) shows an overall decrease from 3 to 1 as N _ { HI } increases in the range 10 ^ { 22 - 24 } { cm ^ { -2 } } .
In the cases of a 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 _ { HI } \sim 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 ratio F ( 6825 ) / F ( 7082 ) of AG Dra is significantly smaller than that of HM Sge , implying that ’ S ’ type symbiotics are characterized by higher N _ { HI } than ’ D ’ type symbiotics .