Alpha Trianguli Australis (α TrA, α Trianguli Australis) is the brightest star in the southern circumpolar constellation Triangulum Australe, forming an apex of a triangle with Beta and Gamma Trianguli Australis that gives the constellation its name (Latin for southern triangle). This star has the traditional name Atria, which is merely a contraction of its Bayer designation.[7] In traditional Chinese it is called 三角形三 (Mandarin: sān jiǎo xín sān), the Third Star of the Triangle.
Alpha Trianguli Australis is a bright giant star with an apparent magnitude of +1.91. Based upon parallax measurements, this star is located roughly 391 light-years (120 parsecs) distant from the Earth.[1] The estimated age of the star is 48 million years old; sufficiently old for a massive star to evolve away from the main sequence and expand into a giant.[3] It has a mass roughly seven times the mass of the Sun, but is emitting about 5,500 times the Sun's luminosity. The effective temperature of the star's outer envelope is 4,150 K,[3] which gives it the characteristic orange hue of a K-type star.[8] With a diameter 130 times that of our sun, it would almost reach the orbit of Venus if placed at the centre of our solar system. The proper name Atria is a contraction of its Bayer designation.[9]
There is evidence that Atria may be a binary star. It displays unusual properties for a star of its class, including stellar flares and a higher than normal emission of X-rays. These can be explained by a young, magnetically active companion with a stellar classification of about G0 V. Such a star would have a mass similar to the Sun, with an orbital period of at least 130 years. Young, G-type stars have a high temperature corona and frequently emit flares causing sudden increases in luminosity. The pair may be separated by about 50 Astronomical Units.[5]