Gamma Trianguli Australis
Star in the constellation Triangulum Australe
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Gamma Trianguli Australis, Latinized from γ Trianguli Australis, is a white-hued star in the southern constellation of Triangulum Australe. Along with Alpha and Beta Trianguli Australis it forms a prominent triangular asterism that gives the constellation its name (Latin for southern triangle). It is the third-brightest member of this constellation with an apparent visual magnitude of +2.87.[2] Based upon parallax measurements, Gamma Trianguli Australis is located at a distance of about 190 light-years (58 parsecs) from Earth.[1]
 | |
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Triangulum Australe |
| Right ascension | 15h 18m 54.58129s[1] |
| Declination | −68° 40′ 46.3680″[1] |
| Apparent magnitude (V) | +2.87[2] |
| Characteristics | |
| Evolutionary stage | Subgiant[3] |
| Spectral type | A1III[3] |
| U−B color index | −0.02[4] |
| B−V color index | +0.00[4] |
| Astrometry | |
| Radial velocity (Rv) | −3.0[2] km/s |
| Proper motion (μ) | RA: −65.816 mas/yr[1] Dec.: −31.187 mas/yr[1] |
| Parallax (π) | 17.1809±0.3327 mas[1] |
| Distance | 190 ± 4 ly (58 ± 1 pc)[1] |
| Absolute magnitude (MV) | −0.89[5] |
| Details | |
| Mass | 3.04[3] M☉ |
| Radius | 6.5 or 7[3] R☉ |
| Luminosity | 249[6] L☉ |
| Surface gravity (log g) | 3.39[7] cgs |
| Temperature | 8,225[3] K |
| Rotational velocity (v sin i) | 199[8] km/s |
| Age | 350[3] Myr |
| Other designations | |
| γ TrA, CD−68°1503, FK5 560, HD 135382, HIP 74946, HR 5671, SAO 253097[9] | |
| Database references | |
| SIMBAD | data |
Characteristics
The spectrum of this star matches a stellar classification of A1 III, which identifies it as a giant star. It could be also a subgiant.[3] An unusual abundance of the element europium demonstrates it to be a peculiar, or Ap star.[10] However, its classification as a chemically peculiar star is doubtful.[3] Most stars of this type are slow rotators,[11] but Gamma Trianguli Australis displays a very high rate of rotation with a projected rotational velocity of 199 km s−1.[8]
At a mass of 3.04 solar masses, Gamma Trianguli Australis was a late B-type star (B8V/B9V) in the main sequence. Being 350 million years old, it has recently begun its expansion towards a red giant. Its radius is either 7 R☉ (estimated using stellar isochrones) or 6.5 R☉ (measured).[3] The star is emitting a luminosity equivalent to 250 solar luminosities.[6] Its surface has an effective temperature of 8,225 K.[3] This is around 2,450 K hotter than the Sun[12] and gives it a white hue, typical of A-type stars.[13]
This star shows an excess emission of infrared radiation, suggesting that there is a circumstellar disk of dust orbiting this star. The mean temperature of the emission is 50 K, corresponding to a separation from the star of 481 astronomical units.[14]
Reported companion star
The Gaia Data Release 3 (Gaia DR3) reported Gamma Trianguli Australis as an astrometric binary with a period of 488 days (1.34 years). The companion star would be a red dwarf with a mass of 0.26 M☉ and a semimajor axis of 1.8 AU. However, a further study using the Very Large Telescope did not find any evidence of a companion, placing constraints on the properties of the putative companion.[3]
Modern legacy
γ TrA appears on the flag of Brazil, symbolising the state of Paraná.[15]