Binary star system in the constellation Triangulum Australe
! style="text-align: center; background-color: #FFFFC0;" colspan="2" | Observation dataEpoch J2000      Equinox J2000
! style="text-align:left" | Constellation
! style="text-align:left" | Right ascension
! style="text-align:left" | Declination
! style="text-align:left" | Apparent magnitude (V)
! style="background-color: #FFFFC0; text-align: center;" colspan="2"| Characteristics
! style="text-align:left" | Spectral type
! style="text-align:left" | U−B 
! style="text-align:left" | B−V 
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Zeta Trianguli Australis (ζ TrA) 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 further 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.
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.
References.
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