Wind mass transfer in S-type symbiotic binaries III. Confirmation of a wind focusing in EG Andromedae from the nebular [OIII]\lambda 5007 line

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 $\varphi = 0.1$, 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.Comment: 10 pages, 8 figure

Density asymmetry and wind velocities in the orbital plane of the symbiotic binary EG Andromedae

Context. Non-dusty late-type giants without a corona and large-scale pulsations represent objects that do not fulfil the conditions under which standard mass-loss mechanisms can be applied efficiently. The driving mechanism of their winds is still unknown. Aims. The main goal of this work is to match the radial velocities of absorbing matter with a depth in the red giant (RG) atmosphere in the S-type symbiotic star EG And. Methods. We measured fluxes and radial velocities of ten FeI absorption lines from spectroscopic observations with a resolution of ~30 000. At selected orbital phases, we modelled their broadened profiles, including all significant broadening mechanisms. Results. The selected FeI absorption lines at 5151 - 6469A, originate at a radial distance ~1.03 RG radii from its centre. The corresponding radial velocity is typically ~1 km/s , which represents a few percent of the terminal velocity of the RG wind. The high scatter of the radial velocities of several km/s in the narrow layer of the stellar atmosphere points to the complex nature of the near-surface wind mass flow. The average rotational velocity of 11 km/s implies that the rotation of the donor star can contribute to observed focusing the wind towards the orbital plane. The orbital variability of the absorbed flux indicates the highest column densities of the wind in the area between the binary components, even though the absorbing neutral material is geometrically more extended from the opposite side of the giant. This wind density asymmetry in the orbital plane region can be ascribed to gravitational focusing by the white dwarf companion. Conclusions. Our results suggest that both gravitational and rotational focusing contribute to the observed enhancement of the RG wind towards the orbital plane, which makes mass transfer by the stellar wind highly efficient.Comment: 12 pages, 10 figure

The secondary minimum in YY Her: Evidence for a tidally distorted giant

We present and analyze quiescent UBVRI light curves of the classical symbiotic binary YY Her. We show that the secondary minimum, which is clearly visible only in the quiescent VRI light curves, is due to ellipsoidal variability of the red giant component. Our simple light curve analysis, by fitting of the Fourier cosine series, resulted in a self-consistent phenomenological model of YY Her, in which the periodic changes can be described by a combination of the ellipsoidal changes and a sinusoidal changes of the nebular continuum and line emission.Comment: 5 pages, 2 figures, to appear in Astronomy & Astrophysic