Astronomical Institute, Slovak Academy of Sciences, SK-059 60 Tatranska
Received August 13, 2007; revised September 3, 2007; accepted September 4, 2007
Abstract I introduce fundamental types of variations observed in the light curves
of symbiotic stars: the orbitally-related wave-like modulation during quiescent
phases, eclipses during active phases, and apparent orbital changes indicated
during transitions between quiescence and activity. I explain their nature with the
aid of the spectral energy distribution of the composite spectrum of symbiotic stars
and their simple ionization model.