A new kind of nova

We performed extensive, multi-wavelength observations of the prototypical symbiotic star Z Andromedae between 2000 and 2003, during a large eruption. The rise to optical maximum occurred in three distinct stages. During the first stage, the rise was very similar to an earlier, small outburst which we determined was due to an accretion-disk instability. In the second stage, an optically thick shell of material was ejected, and in the third stage, the shell cleared to reveal a white dwarf whose luminosity was roughly 10^4 Lsun. We suggest that the outburst was powered by an increase in the rate of nuclear burning on the white-dwarf surface, triggered by a sudden burst of accretion. This outburst thus combined elements of both dwarf novae and classical novae.