EK Trianguli Australis is a

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Triangulum Australe Triangulum Australe is a small constellation in the far Southern Celestial Hemisphere. Its name is Latin for "the southern triangle", which distinguishes it from Triangulum in the northern sky and is derived from the Acute triangle, acute, almost ...

. It is a

dwarf nova A dwarf nova (pl. wiktionary:nova, novae), or U Geminorum variable, is one of several types of cataclysmic variable star, consisting of a close binary star system in which one of the components is a white dwarf that accretion disk, accretes matter ...

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 "

superhump In astronomy, a superhump is a periodic brightness variation in a cataclysmic variable star system, with a period within a few percent of the orbital period of the system. History Superhumps were first seen in SU Ursae Majoris (SU UMa) stars, a su ...

s" of heightened activity. The distance of the system has been assumed at 180 parsecs (586 light years) from the Solar System, for the

donor star In astronomy, the Roche lobe is the region around a star in a binary system within which orbiting material is gravitationally bound to that star. It is an approximately teardrop-shaped region bounded by a critical gravitational equipotential, wi ...

(assumed to be a

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

that is nondetectable at that range). Spectroscopic analysis and calculation gave an estimate of 125 parsecs (407.5 light years). The system consists of a

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

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 An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and ...

and periodically erupts, reaching

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

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 the Sun. Up to 75% of the brightness of the object comes from the accretion disc, which is heated to a temperature of 6500 K.

References

{{DEFAULTSORT:EK Trianguli Australis Triangulum Australe Dwarf novae Trianguli Australis, EK