Alpha Trianguli Australis
 Location of α Trianguli Australis (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Triangulum Australe |
| Right ascension | 16h 48m 39.89508s |
| Declination | –69° 01′ 39.7626″ |
| Apparent magnitude (V) | 1.91 |
| Characteristics | |
| Spectral type | K2 IIb-IIIa |
| U−B color index | +1.56 |
| B−V color index | +1.44 |
| Astrometry | |
| Radial velocity (Rv) | –3.3 km/s |
| Proper motion (μ) |
RA: 17.99 mas/yr Dec.: –31.58 mas/yr |
| Parallax (π) | 8.35 ± 0.15mas |
| Distance | 391 ± 7 ly (120 ± 2 pc) |
| Absolute magnitude (MV) | –3.68 |
| Details | |
| Mass | 7 M☉ |
| Luminosity | 5,500 L☉ |
| Surface gravity (log g) | 1.5 cgs |
| Temperature | 4,150 K |
| Metallicity [Fe/H] | –0.06 dex |
| Age | 4.8 × 107 years |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Trianguli Australis (α Trianguli Australis, abbreviated Alpha TrA, α TrA), also named Atria, is the brightest star in the southern constellation of Triangulum Australe, forming an apex of a triangle with Beta and Gamma Trianguli Australis that gives the constellation its name (Latin for southern triangle).
α Trianguli Australis (Latinised to Alpha Trianguli Australis) is the star's Bayer designation. The historical name Atria is a contraction. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Atria for this star.
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. 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. 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, which gives it the characteristic orange hue of a K-type star. With a diameter 130 times that of the Sun, it would almost reach the orbit of Venus if placed at the centre of the Solar System.
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