THE EFFECT OF THE MAGNETIC-FIELD OF THE SECONDARY STAR IN DWARF NOVAE

We investigate the effect of a secondary star magnetic field on the ac cretion disc dynamics of dwarf novae. Simulations have been carried ou t with a particle code and a dipolar magnetic field structure. The mag netic field acts to remove angular momentum from the disc material, in creasing the inward mass flow. This makes the accretion disc more cent rally condensed, causing a reduction in the recurrence time for dwarf nova outbursts. We have produced Doppler tomograms and light curves wh ich may be compared with observations. These tomograms are significant ly different from those produced in the absence of a magnetic held on the secondary. We derive an upper limit to the magnetic moment of the secondary star in U Gem of mu(2) < 2 x 10(32) A m(2). The magnetic tru ncation of the accretion disc produces resonance phenomena similar to those seen in the superoutbursts of SU UMa systems. While these have n ot been observed for systems like U Gem, observations of the SU UMa sy stems provide us with a useful diagnostic of the disc-field interactio n. We are able to place an upper limit on the magnetic moment of the s econdary in Z Cha of mu(2) < 1 x 10(30) A m(2).