1998AJ....116..444M

An analysis of the observed radial velocities in the system CH Cygni has been conducted in the framework of three-body dynamics. The observations and the fact that this star began symbiotic-like activity in the beginning of the 1960s can be explained in terms of a model consisting of a close binary of total mass ∼4 M_☉ that is orbited by a normal white dwarf of mass ∼1 M_☉. The 4 M_☉ binary consists of a red giant of mass ∼3.5 M_☉ and a ∼0.5 M_☉ dim star of unknown type, which is probably difficult to detect observationally. The orbit of this inner binary has high inclination (more than 40°) with respect to the orbit of the white dwarf. The dynamical phenomenon known as the Kozai resonance then causes large long-period eccentricity variations in the inner binary. When in the high-eccentricity state, the binary expels gas out of the red giant. Part of this ends up on the white dwarf, causing the activity. In our model, the eccentricity of the binary was low for a long time and has been growing steadily during this century. This explains the only recent symbiotic activity.