Dwarf Nova Outbursts. III. The Viscosity Parameter α

Visual light curves based on dwarf nova models, covering a broad range of relevant parameters, are used to determine the widths of outbursts, rates of decline, and UV delays, as well as their dependence on the orbital period. From a comparison with the observational data it is found that the value of α on the hot branch of the Σ-Te relation is αhot≈0.2. An important test is also made concerning the tidal radii of disks. A comparison of the absolute visual magnitudes at maximum, obtained from model light curves, with the observed MV(max) gives Rtid/RRoche≈0.9, which is the standard value used in model calculations.