STROMGREN PHOTOMETRY OF DWARF NOVAE

A sample of twenty six dwarf novae was observed in the Stromgren photo metric system. The objects show unique photometric characteristics in this system, both in quiescence and outburst. We find that in the bina ries with non-detected secondary stars, v-b remains constant independe ntly of y magnitude, while b-y has a broad range and Hbeta increases w ith b-y. In dwarf novae with detected secondaries Hbeta decreases as b -y increase. We interpret these observations as a consequence of diffe rent mass accretion rates with discs having a broad range of external or minimum temperatures T(min), with Hbeta increasing to a maximum for discs with T(min) around 6000 K. A constant v-b value indicates that there must be a redistribution of photons cooling the disc via Hdelta, such that the line plus adjacent continuum flux remains constant rela tive to the continuum flux around 4700 angstrom.