The precursor to a nova, which is expected to be a form of cataclysmic binary. To date, no object that has been studied in detail has subsequently become a nova, but some novae have been identified on earlier photographs. Of the few pre-outburst light-curves that can be constructed, some appear to show a rise in brightness of 1–4 mag. (perhaps with oscillations), over a period of 1–5 years before the explosion.