2000A&A...359..998B

The scatter in the light curves of four eclipsing cataclysmic variables (CVs) is analyzed in order to find constraints for the location of the flickering light source in these systems. In all cases the ``scatter curves'' contain well defined eclipses which begin and end exactly at the phases of eclipse ingress and egress of individual system components: In HT Cas, V2051 Oph and UX UMa the scatter eclipse coincides with the white dwarf eclipse, in IP Peg with the hot spot eclipse. Moreover, in V2051 Oph, IP Peg and UX UMa the scatter is enhanced during phases of visibility of the hot spot. Together with similar results from earlier investigations these findings leave little doubt that the flickering in CVs can originate in two regions: the innermost accretions disk with the boundary layer and the white dwarf surface, and the region of impact of the stream of transferred matter from the secondary star upon the accretion disk. Two different techniques (termed `single' and `ensemble' method) to measure the scatter curves of CVs are advocated in the literature. A critical comparison of these techniques is performed. It is found that the `ensemble' method yields reasonable results only under specific circumstances.