High-speed photometry of Z Chamaeleontis in the quiescent state

We present high-speed photometry of the dwarf nova Z Cha. The total duration of the primary eclipse implies a lower limit of ∼ 0.51 ± 0.08 M0† for the mass of the white dwarf. The eclipse of the hotspot is more pronounced in comparison with previous observations, and shows at least two types of structure. Using the relationship between the mass ratio and inclination in this system, together with theoretical stream trajectories, we find that a mass ratio of between 5 and 7 is required to explain the phasing of the hotspot eclipse relative to the primary eclipse. The hotspot varies in size and location in the disc, but always indicates an outer radius for the accretion disc/ring which is about twice that of theoretical inviscid discs. The mass ratio limits, coupled with limitations on the size of the central source, indicate that the central source may have a disc component. It is found that, on occasion, the hotspot extends into the innermost regions of the accretion disc indicating that the stream thickness is, at times, larger than that of the outer disc. We suggest that these extended hotspots have consequences for the interpretation of radial velocity measurements from the wings of emission lines.