Creation of neutral disks during outbursts of symbiotic binaries

Abstract

Multiwavelength modelling of the spectral energy distribution of symbiotic binaries suggests that a neutral disk-like zone is created around the hot star near the orbital plane during active phases. Presumably, this is connected with the enhanced wind from the active hot star. To test this idea, we applied the wind compression model to active hot stars in symbiotic binaries, within which the wind particles are compressed more to the equatorial plane due to a fast rotation of the hot star. Accordingly, we calculated the ionization structure for such compressed wind and ionizing photons from the hot star. We found that the hot star wind, enhanced during active phases to \sim (10^-7 - 10^-6) M_sun yr^-1, and the rotational velocity of 100 - 350 km s^-1 at the star's equator lead to formation of a neutral disk-shaped zone. The presence of such disks is transient, being connected with the active phases of symbiotic binaries. During quiescent phases, such neutral disks cannot be created, because of insufficient mass loss rate.