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An ancient nova shell around the dwarf nova Z Camelopardalis


Cataclysmic variables (classical novae and dwarf novae) are binary star systems in which a red dwarf transfers hydrogen-rich matter, by way of an accretion disk, to its white dwarf companion1. In dwarf novae, an instability2 is believed to episodically dump much of the accretion disk onto the white dwarf. The liberation of gravitational potential energy then brightens these systems by up to 100-fold every few weeks or months2. Thermonuclear-powered eruptions thousands of times more luminous3,4 occur in classical novae5, accompanied by significant mass ejection6 and formation of clearly visible shells7,8 from the ejected material. Theory predicts that the white dwarfs in all dwarf novae must eventually accrete enough mass to undergo classical nova eruptions9. Here we report a shell, an order of magnitude more extended than those detected around many classical novae, surrounding the prototypical dwarf nova Z Camelopardalis. The derived shell mass matches that of classical novae, and is inconsistent with the mass expected from a dwarf nova wind or a planetary nebula. The shell observationally links the prototypical dwarf nova Z Camelopardalis with an ancient nova eruption and the classical nova process.

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Figure 1: GALEX satellite image of the field of the dwarf nova Z Camelopardalis on 25 January 2004.
Figure 2: Features around Z Cam.
Figure 3: All fields imaged by GALEX before July 2006, with centres within 200 arcmin of Z Cam.
Figure 4: Emission lines from the Z Cam nebulosity.

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This work was supported by the National Aeronautics and Space Administration. Telescope time at the Kitt Peak National Observatory, Lick Observatory and the Palomar Observatory is gratefully acknowledged. Kitt Peak National Observatory of the National Optical Astronomy Observatory is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.

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Correspondence to Michael M. Shara.

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Shara, M., Martin, C., Seibert, M. et al. An ancient nova shell around the dwarf nova Z Camelopardalis. Nature 446, 159–162 (2007).

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