Nova outbursts on rotating oblate white dwarfs

A novel hypothesis is proposed in which the prolate geometry and latitudina l abundance gradients observed in nova ejecta are simultaneously explained as a natural consequence of the rotation and oblate distortion of the white dwarf. Thermonuclear runaway on the surface of an oblate rotating white dw arf is strongly affected by the local gravity, leading to stronger outburst s and faster outflows at the poles than in the equatorial regions. A unifie d scheme is presented which is capable of explaining the gross structures o f the shells of classical novae, those 'recurrent novae' with giant compani ons, and symbiotic novae, which also show evidence for bipolar outbursts. I t is shown that this hypothesis is capable of producing the observed geomet ry of the ejecta of the classical novae DQ Her 1934, V1500 Cyg 1975 and GK Per 1901, the recurrent nova RS Oph (1985 outburst), and the symbiotic nova HM Sge. Some observationally testable predictions which follow from this h ypothesis are discussed.