2012A&A...538A..94K

We present results of spectroscopic observations of SS Cygni performed at the 1.5 m telescope of the Loiano Observatory in June 2009, three days before a long outburst. Using results of these observations, we computed Doppler tomograms in three Balmer lines H_β, H_γ, and H_δ. Analyzing the tomograms, we identified gas dynamic features existing in the system. It is shown that in the pre-outburst disk a number of shock waves exist. These waves are ``hot line'' a wave produced by the interaction between the circum-disk halo and the stream from the inner Lagrangian point L₁, and two arms of the spiral tidal shock and bow shock caused by the motion of the accretor and disk in the gas of the circum-binary envelope. We also found that before the outburst the density and size of the disk increase.