Stromgren photometry of dwarf novae.

A sample of twenty six dwarf novae was observed in the Strömgren photometric system. The objects show unique photometric characteristics in this system, both in quiescence and outburst. We find that in the binaries with non-detected secondary stars, υ - b remains constant independently of y magnitude, while b - y has a broad range and Hβ increases with b - y. In dwarf novae with detected secondaries Hβ decreases as b - y increase. We interpret these observations as a consequence of different mass accretion rates with discs having a broad range of external or minimum temperatures T_min, with Hβ increasing to a maximum for discs with T_min around 6000 K. A constant υ - b value indicates that there must be a redistribution of photons cooling the disc via Hδ, such that the line plus adjacent continuum flux remains constant relative to the continuum flux around 4700 Å.