The response of a dwarf nova disc to real mass transfer variations

We present simulations of dwarf nova outbursts taking into account realisti c variations of the mass loss rate from the secondary. The mass transfer va riation has been derived from 20 years of visual monitoring and from X-ray observations covering various accretion states of the discless cataclysmic variable AM Herculis. We find that the outburst behaviour of a fictitious d warf nova with the same system parameters as AM Her is strongly influenced by these variations of the mass loss rate. Depending on the mass loss rate, the disc produces either long outbursts, a cycle of one long outburst foll owed by two short outbursts, or only short outbursts. The course of the tra nsfer rate dominates the shape of the outbursts because the mass accreted d uring an outburst cycle roughly equals the mass transferred from the second ary over the outburst interval. Only for less than 10% of the simulated tim e, when the mass transfer rate is nearly constant, the disc is in a quasi-s tationary state during which it periodically repeats the same cycle of outb ursts. Consequently, assuming that the secondary stars in non-magnetic CV's do not differ from those in magnetic ones, our simulation indicates that p robably all dwarf novae are rarely in a stationary state and are constantly adjusting to the prevailing value of the mass transfer rate from the secon dary.