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IP Peg
The light curves of IP Peg differ strongly from those of HT Cas and V2051 Oph. As an example the B light curve (Stiening system) of 1992, November 27, is shown in Fig. 5a. It is dominated by an exceptionally strong hump which reaches a peak flux approximately three times as high as the flux around phase -0.4 where the hump is invisible. The eclipse is characteristically structured: A steep part of the ingress caused by the white dwarf ingress is followed by a more gradual part due to the hot spot ingress. Unlike in the classical SU UMa systems OY Car and Z Cha, however, white dwarf and hot spot ingress cannot be separated. The white dwarf egress is in most cycles discernible as a discrete step in the light curve. Somewhat later a second step marks the egress of the hot spot.
In view of the variations of the location of the hot spot in the system the corresponding contact phases are not very stable as was shown by [Wood et al. (1989b)]. The lateral dashed lines in Fig. 5 represent the mean first and last hot spot eclipse contacts as measured in the present light curves. The central line marks the mean white dwarf egress phase determined by [Wood et al. (1989b)].
The general character of the short term variations of IP Peg is different from that of other CVs. Significant variations above the noise level are only seen during the presence of the orbital hump, suggesting that the hot spot is the culprit. This is confirmed by the more formal scatter analysis.
The mean scatter curve of IP Peg (Fig. 5b) was measured in the same way as in the previous cases. Since it is based on only three light curves the noise is particularly large. For the same reason it is not sensible to derive formal errors in the way done for the other stars in this study. Nevertheless there is no doubt that it is significantly different from the corresponding curves for the other stars. The strong increase of the scatter at the phases when the orbital hump is visible indicates that the flickering in IP Peg is dominated by the hot spot. In contrast to Z Cha (Bruch 1996) and V2051 Oph (Sect. 4.2) where the scatter eclipse ends with the white dwarf eclipse even if the hot spot continues to be eclipsed, there is no significant increase of the scatter of IP Peg when the white dwarf eclipse ends. The scatter only increases when the hot spot emerges from the eclipse (the single high point just at white dwarf egress is an artifact due to the same effect which produces the spurious peaks in the HT Cas scatter curve; see Sect. 4.1).
Recognizing that the scatter at phases when the hot spot is invisible is as small as during eclipse centre indicates that in this particular system the accretion disk/white dwarf contributes practically nothing to the total flickering.
Since these conclusions are based on only three light curves, they may not be as firm as concerning the other stars of this study. However, it does not appear likely that the light curves used here which are very similar to each other are wholly atypical for IP Peg.