EK Trianguli Australis
EK Trianguli Australis is a star in the constellation Triangulum Australe. It is a dwarf nova of the SU Ursae Majoris type that officially classified as such in 1980, after the characteristic eruptions of a short eruption and a supereruption were observed in May 1978 and June 1979 respectively. These systems are characterised by frequent eruptions and less frequent supereruptions. The former are smooth, while the latter exhibit short "superhumps" of heightened activity. The distance of the system has been assumed at 180 parsecs from the Solar System, for the donor star. Spectroscopic analysis and calculation gave an estimate of 125 parsecs.
The system consists of a white dwarf and a donor star which orbit around a common centre of gravity every 1.5 hours. The white dwarf sucks matter from the other star onto an accretion disc and periodically erupts, reaching apparent magnitude 11.2 in superoutbursts, 12.1 in normal outbursts and remaining at magnitude 16.7 when quiet. The "superhumps" see the star increase by 0.24 magnitude for 1.55 hours during these superoutbursts.
Spectroscopic observations of the white dwarf with the Hubble Space Telescope and Space Telescope Imaging Spectrograph reveal it to be spinning at a speed of 200 km/s, with a surface temperature of 18800 K and is estimated to have 0.6 the mass of our sun. Up to 75% of the brightness of the object comes from the accretion disc, which is heated to a temperature of 6500 K.
