ИСТИНА

In symbiotic binaries, two very different temperature regimes of the circumstellar material exist side by side. Around the donor red giant star, there is a neutral, cool and dense environment of its stellar wind, while around the hot component, physical processes take place at temperatures of the order of 105 K, thus ionizing the surrounding medium. The hot component is in most cases a very hot and luminous white dwarf accreting the giant’s wind. However, the accretion rates that can be achieved by the standard Bondi-Hoyle wind accretion are too low to power the high luminosities of the accretor. We found two independent indications of wind focusing towards the orbital plane that affects the efficiency of mass transfer. By modelling the measured neutral hydrogen column densities from Rayleigh scattering along multiple lines of sight for two quiet high-inclination symbiotic systems, EG And and SY Mus, we found higher densities at the orbital-plane than can correspond to a spherically-symmetric wind. Consistently, the orbital variability of [OIII] 5007Å line in EG And points to diluted wind matter around the poles of the red giant. Yet another asymmetry within the orbital plane was revealed by modelling the spectral profiles of 10 Fe I absorption lines. The maximal absorbed fluxes measured around the superior conjunction of the white dwarf result from a higher-density red giant wind located in the direction towards the white dwarf. This asymmetry supports gravitational focusing as the mechanism responsible for the observed wind enhancement towards the orbital plane. Also, the measured giant’s rotational velocity of 11 km/s is sufficiently high for rotationally-induced focusing of the wind to contribute to this pole-orbital plane density asymmetry.