Late superhumps and the stream-disc impact in IYUMa

We use the hotspot eclipse times of the newly discovered deeply eclipsing d warf nova IY UMa to trace out the shape of its disc during the late superhu mp era. We find an eccentric disc. We show that the brightness of the strea m-disc impact region varies as expected with \DeltaV\(2), where DeltaV is t he relative velocity of the stream with respect to the velocity of the disc at the impact point. We conclude that the hotspot is the source of late su perhump light.