Wind mass transfer in S-type symbiotic binaries III. Confirmation of a wind focusing in EG Andromedae from the nebular [OIII]λ5007 line

Abstract

Context. The structure of the wind from the cool giants in symbiotic binaries carries important information for understanding the wind mass transfer to their white dwarf companions and its fuelling. Aims. In this paper, we indicate a non-spherical distribution of the neutral wind zone around the red giant (RG) in the symbiotic binary star, EG And. Methods. We achieved this aim by analysing the periodic orbital variations of fluxes and radial velocities of individual components of the H$\alpha$ and [OIII]$\lambda$5007 lines observed on our high-cadence medium (R $\sim$ 11 000) and high-resolution (R $\sim$ 38 000) spectra. Results. The asymmetric shaping of the neutral wind zone at the near-orbital-plane region is indicated by: (i) the asymmetric course of the H$\alpha$ core emission fluxes along the orbit; (ii) the presence of their secondary maximum around the orbital phase $\phi =0.1$, which is possibly caused by the refraction effect; and (iii) the properties of the H$\alpha$ broad wing emission originating by Raman scattering on H${}^0$ atoms. The wind is substantially compressed from polar directions to the orbital plane as constrained by the location of the [OIII]$\lambda$5007 line emission zones in the vicinity of the RG at/around its poles. The corresponding mass-loss rate from the polar regions of $\lesssim 10^{-8}$ Msun/yr is a factor of $\gtrsim 10$ lower than the average rate of $\approx 10^{-7}$Msun/yr derived from nebular emission of the ionised wind from the RG. Furthermore, it is two orders of magnitude lower than that measured in the near-orbital-plane region from Rayleigh scattering. Conclusions. The startling properties of the nebular [OIII]$\lambda$5007 line in EG And provides an independent indication of the wind focusing towards the orbital plane.

10 pages, 8 figures

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• Numerical Simulations of Wind Accretion in Symbiotic Binaries
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• THA 15-31: Discovery with VLT/X-Shooter and Swift/UVOT of a new symbiotic star of the accreting-only variety
• DeGaPe 35: Amateur discovery of a new southern symbiotic star
• Symbiotic Stars in the APOGEE Survey: The Case of LIN 358 and SMC N73 (LIN 445a)
• Multiwavelength modeling the SED of Luminous Supersoft X-ray Sources in Large Magellanic Cloud and Small Magellanic Cloud
• The emergence of a neutral wind region in the orbital plane of symbiotic binaries during their outbursts