  The modeling of UV and optical spectra emitted from the symbiotic system AG
Draconis, adopting collision of the winds, predicts soft X-ray bremsstrahlung
from nebulae downstream of the reverse shock with velocities > 150 km/s and
intensities comparable to those of the white dwarf black body flux. At
outbursts, the envelop of debris, which corresponds to the nebula downstream of
the high velocity shocks (700-1000 km/s) accompanying the blast wave, absorbs
the black body soft X-ray flux from the white dwarf, explains the broad
component of the H and He lines, and leads to low optical-UV-X-ray continuum
fluxes. The high optical-UV flux observed at the outbursts is explained by
bremsstrahlung downstream of the reverse shock between the stars. The depletion
of C, N, O, and Mg relative to H indicates that they are trapped into dust
grains and/or into diatomic molecules, suggesting that the collision of the
wind from the white dwarf with the dusty shells, ejected from the red giant
with about 1 year periodicity, leads to the U-band fluctuations during the
major bursts.
