Balmer decrements in dwarf novae

Abstract

We investigate the question of the possible variable conditions in dwarf novae. The Balmer decrements are used as variability indicators due to their form being strongly dependent on the conditions in the radiating medium. It is shown that the decrements are usually anomalous and variable in time at minimum light, which indicates a variability of the conditions in the radiating medium. The spectrum changes significantly during the outburst state, the decrement becomes steep and has no anomalies. It appears that the outburst makes the emitting region more homogeneous and sparse. Another possible explanation is that the radiation is emitted by some other region, unseen at minimum light.