1998A&A...336L..73N

We present a study of the observable spectral manifestations associated with spiral shocks within quiescent accretion disks and compare them with observations of the dwarf nova U Geminorum. Our results indicate that the orbital behaviour of the hydrogen emission line profile in the spectrum of U Gem can be reproduced via a simple model of the accretion disk with two symmetrically located spiral shocks with the spiral angle θ about 60°. This provides for the first time convincing evidence for the existence of spiral shocks in the accretion disk of a cataclysmic variable in quiescence.