Dwarf nova outbursts. I. The UV delay

Models of dwarf nova outbursts are calculated for a range of relevant param eters: the masses of the components which determine the orbital period and the radius of the disk, the mass transfer rate, and the viscosity parameter alpha. The visual (lambda 5500 Angstrom) and ultraviolet (lambda 1200 Angs trom) light curves are calculated using black body and Kurucz fluxes. The r esulting UV delays show strong dependence on model parameters and, in parti cular, confirm the existence of a dichotomy between Type A and Type B outbu rsts. The model predicted UV delays agree quite well with observations, wit h the "best-fit" for alpha(hot) between 0.1 and 0.2. Earlier, negative conc lusions and the controversy around the "problem of UV delay" resulted prima rily from incorrect outer boundary conditions and other model simplificatio ns.