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White dwarfs are routinely observed to have polluted atmospheres, andsometimes significant infrared excesses, that indicate ongoing accretion ofcircumstellar dust and rocky debris. Typically this debris is assumed to be inthe form of a (circular) disc, and to originate from asteroids that passedclose enough to the white dwarf to be pulled apart by tides. However,theoretical considerations suggest that the circularisation of the debris,which initially occupies highly eccentric orbits, is very slow. We thereforehypothesise that the observations may be readily explained by the debrisremaining on highly eccentric orbits, and we explore the properties of suchdebris. For the generic case of an asteroid originating at several au from thewhite dwarf, we find that all of the tidal debris is always bound to the whitedwarf and that the orbital energy distribution of the debris is narrow enoughthat it executes similar elliptical orbits with only a narrow spread. Assumingthat the tidal field of the white dwarf is sufficient to minimise the effectsof self-gravity and collisions within the debris, we estimate the time overwhich the debris spreads into a single elliptical ring, and we generate toyspectra and lightcurves from the initial disruption to late times when thedebris distribution is essentially time steady. Finally we speculate on theconnection between these simple considerations and the observed properties ofthese systems, and on additional physical processes that may change this simplepicture.

Emission from elliptical streams of dusty debris around white dwarfs