Zeta Trianguli Australis
Zeta Trianguli Australis is a spectroscopic binary star system in the southern constellation Triangulum Australe. The pair have a combined apparent visual magnitude of 4.90, which is bright enough to be visible to the naked eye. Based on parallax measurements, the system is located at a distance of approximately 39.4 light years from Earth. After closing to within some 436,600 years ago, it is now drifting farther away with a radial velocity of +8.3 km/s.
The pair orbit each other once every 13 days, and the orbital eccentricity is a low 0.014, making their orbit nearly circular. The primary component has a stellar classification of F9V, matching an F-type main-sequence star. It has a mass equal to 1.12 times the mass of the Sun, a radius 1.06 times the radius of the Sun, and irradiated at an effective temperature of, slightly hotter than the Sun as well. The companion is a small red dwarf star with a class in the range of M1–7V and 40% of the Sun's mass. The age of the system is estimated at 600–900 million years.
Any objects orbiting the pair in a circumbinary orbit should have an orbital separation of 0.217 AU or higher; otherwise its orbit would be unstable due to gravitational interactions.
Somewhat surprisingly for a star located at a declination of 70° S, it is a candidate swarm member of the Ursa Major moving group. However, there is some evidence to the contrary.