The symbiotic system Z Andromedae : a spectral analysis of the anomalous   1984-1986 outburst
  The visual magnitude profile of the symbiotic system Z And during the 1984-1986 activity period appears double peaked and the flux intensity is low compared to outbursts in other epochs. The detailed modeling of the observed spectra, accounting for the shells ejected by the red giant star, shows that the outburst is intrinsically single but distorted by the collision at different phases of the white dwarf wind with two close shells. 
M. Contini
astro-ph.SR