Ionization structure of hot components in symbiotic binaries during active phases

Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranská Lomnica, Slovakia
e-mail: zcarikova@ta3.sk; skopal@ta3.sk

Received: 14 March 2012
Accepted: 24 September 2012

Abstract

Context. During active phases of symbiotic binaries, an optically thick medium in the form of a flared disk develops around their hot stars. During quiescent phases, this structure is not evident.

Aims. We propose the formation of a flared neutral disk-like structure around the rotating white dwarf (WD) in symbiotic binaries.

Methods. We applied the wind compression model and calculated the ionization boundaries in the compressed wind from the WD using the equation of photoionization equilibrium.

Results. During active phases, the compression of the enhanced wind from the rotating WD can form a neutral disk-like zone at the equatorial plane, while the remainder of the sphere above/below the disk is ionized. The hydrogen column density throughout the neutral zone and the emission measure of the ionized fraction of the wind, calculated for the mass loss rate from the WD, Ṁ = 2×10^-6 M_⊙ yr^-1 with v_∞ = 2000 km s^-1, are consistent with those derived from observations. During quiescent phases, the neutral disk-like structure cannot be created because of insufficient mass loss rate.

Conclusions. Formation of the neutral disk-like zone at the equatorial plane is connected with the enhanced wind from the rotating WD, observed during active phases of symbiotic binaries. This probably represents a common origin of warm pseudophotospheres, indicated in the spectrum of active symbiotic binaries with a high orbital inclination.