Z Camelopardalis -- click on the above image to view the full image.

Cataclysmic variables (classical novae and dwarf novae) are binary star systems in which a red dwarf transfers hydrogen-rich matter to its white dwarf companion. In dwarf novae, an instability is believed to episodically dump much of the accretion disk onto the white dwarf, brightening these systems every few weeks or months. Thermonuclear-powered eruptions a thousand times more luminous occur in classical novae, accompanied by significant mass ejection and formation of clearly visible shells. Theory predicts that the white dwarfs in all dwarf novae must eventually accrete enough mass to undergo classical nova eruptions, but not a single dwarf nova has ever been shown to have undergone a classical nova eruption. Recent observations by the NASA ultraviolet satellite  telescope  GALEX have revealed the shell of the prototypical dwarf nova Z Camelopardalis. This shell is about ten times more extended than any detected around any classical nova. The derived shell mass matches that of classical novae, and is inconsistent with the mass expected from a steady dwarf nova wind. Thus the shell mass and morphology observationally link, for the first time, a dwarf nova with the classical nova process...just as theory predicts.

Z Camelopardalis (Z Cam) is one of the brightest dwarf novae in the sky, and at a distance of 163 parsecs (1 pc = 3.26 light-year ), it is also one of the closest. About every 20 days it brightens by up to a factor of 40 (to apparent visual magnitude ~ 10), returning to minimum a few days later. The ultraviolet GALEX image shows Z Cam as the bright central star, and the material ejected hundreds or thousands of years ago during the last nova eruption of Z Cam.

This work was carried out by Michael Shara of AMNH, with collaborators C. Martin, M. Seibert, R. M. Rich, S. Salim, D. Reitzel, D. Schiminovich, C. Delyannis, A. R. Sarrazine, N. Brosch, S. Lépine, D. Zurek, O. De Marco and G. Jacoby