A Monte Carlo Study of Flux Ratios of Raman Scattered O~VI Features at 6825 Å 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 6825 Å and 7082 Å, which are formed via Raman scattering of \ion{O}{6}$\lambda \lambda$ 1032 and 1038 with atomic hydrogen. We adopt a Monte Carlo technique to generate the same number of \ion{O}{6}$\lambda$1032 and $\lambda$1038 line photons and compute the flux ratio $F(6825)/F(7082)$ of these Raman scattered \ion{O}{6} features formed in neutral regions with a simple geometric shape as a function of \ion{H}{1} column density $N_{HI}$. In cylindrical and spherical neutral regions with the \ion{O}{6} 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 $10^{22-24}\mathrm{c}{\mathrm{m}}^{-2}$. In the cases of a slab geometry and other geometries with the \ion{O}{6} source outside the \ion{H}{1} region, Rayleigh escape operates to lower the flux ratio considerably. For moderate values of $N_{HI}\sim 10^{23}\mathrm{c}{\mathrm{m}}^{-2}$ 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 \ion{O}{6}$\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 {\it 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.

15 pages, 9 figures, accepted for publication in ApJ

References in corpus (2)

• Raman Scattered O VI $\lambda$ 6825 and the Accretion Disk Emission Model in the Symbiotic Stars V1016 Cygni and HM Sagittae
• Optical Flickering of the recurrent nova RS Ophiuchi: amplitude - flux relation

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• Stellar Wind Accretion and Raman Scattered O VI Features in the Symbiotic Star AG Draconis