SECULAR BRIGHTNESS VARIATION OF THE DWARF NOVA Z-CHA DURING QUIESCENCE

We report results of long-term optical photometry of the dwarf nova Z Cha made during two quiescent intervals. We find that the brightness of the 'hot spot' increases between two outbursts. This is consistent with the decrease of the outer disc radius previously reported by O'Donoghue. The fluxes of the accretion disc and of the white dwarf do not show a secular trend between outbursts. This result, which reinforces a similar result obtained from long-term observations of VW Hyi, seems hard to reconcile with current versions of the disc-instability model for dwarf-nova outbursts. © Royal Astronomical Society.