Stellar Wind Accretion and Raman O VI Spectroscopy of the Symbiotic Star AG Draconis

  • Published : 2018.05.08

Abstract

High resolution spectroscopy of the yellow symbiotic star AG Draconis is performed with the Canada-France-Hawaii Telescope to analyse the line profiles of Raman scattered O VI broad emission features at $6825{\AA}$ and $7082{\AA}$ with a view to investigating the wind accretion process from the mass losing giant to the white dwarf. These two spectral features are formed through inelastic scattering of O $VI{\lambda}{\lambda}32$ and 1038 with atomic hydrogen. We find that these features exhibit double-component profiles with red parts stronger than blue ones with the velocity separation of ~ 60 km s-1 in the O VI velocity space. Monte Carlo simulations for O VI line radiative transfer are performed by assuming that the O VI emission region constitutes a part of the accretion flow around the white dwarf and that Raman O VI features are formed in the neutral part of the slow stellar wind from the giant companion. The overall Raman O VI profiles are reasonably fit with an azimuthally asymmetric accretion flow and the mass loss rate ~ 4 ${\times}$ 10^{-7} M_sun yr^{-1}. We also find that additional bipolar neutral regions moving away with a speed ~ 70 km s^{-1} in the directions perpendicular to the orbital plane provide considerably improved fit to the red wing parts of Raman features.

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