A superoutburst of the dwarf nova EK Trianguli Australis.

Abstract

Simultaneous UV and optical spectrophotometry were obtained during several stages of a superoutburst of EK TrA. The observed spectra are compared with steady disc models, built both of blackbodies or Kurucz stellar atmospheres and with optically thin contributions. Atmosphere models predict much lower mass transfer rates than blackbody models. Assuming a quasi-steady disc, the size of the optically thick portion decreases between the peak and decline of the superoutburst. The existence of the optical superhump is confirmed and its large amplitude favors a disc hotspot explanation. The line spectra change from absorption to emission during decline, and the C IV (1550) line shows a P Cygni feature of variable profile.