Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-11-07
Mon.Not.Roy.Astron.Soc.375:105-114,2007
Astronomy and Astrophysics
Astrophysics
12 pages, 11 figures, accepted by MNRAS
Scientific paper
10.1111/j.1365-2966.2006.11252.x
We argue that the quiescent value of the viscosity parameter of the accretion disc in WZ Sge may be alpha_{cold}~0.01, in agreement with estimates of alpha_{cold} for other dwarf novae. Assuming the white dwarf in WZ Sge to be magnetic, we show that, in quiescence, material close to the white dwarf can be propelled to larger radii, depleting the inner accretion disc. The propeller therefore has the effect of stabilizing the inner disc and allowing the outer disc to accumulate mass. The outbursts of WZ Sge are then regulated by the (magnetically determined) evolution of the surface density of the outer disc at a radius close to the tidal limit. Numerical models confirm that the recurrence time can be significantly extended in this way. The outbursts are expected to be superoutbursts since the outer disc radius is forced to exceed the tidal (3:1 resonance) radius. The large, quiescent disc is expected to be massive, and to be able to supply the observed mass accretion rate during outburst. We predict that the long-term spin evolution of the white dwarf spin will involve a long cycle of spin up and spin down phases.
Matthews O. M.
Speith Roland
West Richard G.
Wynn Graham A.
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