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

Abstract

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 6825Å and 7082Å, which are formed via Raman scattering of O VIλλ 1032 and 1038 with atomic hydrogen. We adopt a Monte Carlo technique to generate the same number of O VIλ1032 and λ1038 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 ∼ 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 VIλλ1032, 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.