Gamma Trianguli Australis

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Gamma Trianguli Australis
Diagram showing star positions and boundaries of the Triangulum Australe constellation and its surroundings
Cercle rouge 100%.svg
Location of γ Trianguli Australis (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Triangulum Australe
Right ascension  15h 18m 54.58198s[1]
Declination –68° 40′ 46.3654″[1]
Apparent magnitude (V) +2.87[2]
Spectral type A1 V[3][4]
U−B color index –0.02[5]
B−V color index +0.00[5]
Radial velocity (Rv)–3.0[2] km/s
Proper motion (μ) RA: –66.58[1] mas/yr
Dec.: –32.31[1] mas/yr
Parallax (π)17.74 ± 0.12[1] mas
Distance184 ± 1 ly
(56.4 ± 0.4 pc)
Absolute magnitude (MV)−0.89[6]
Mass1.99[7] M
Radius5.86[8] R
Luminosity249[9] L
Surface gravity (log g)3.39[7] cgs
Temperature9,306±316[7] K
Rotational velocity (v sin i)199[4] km/s
Age260[10] Myr
Other designations
γ TrA, CD−68° 1503, FK5 560, HD 135382, HIP 74946, HR 5671, SAO 253097[11]
Database references

Gamma Trianguli Australis (γ Trianguli Australis) is a single,[12] 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 184 light-years (56 parsecs) from Earth.[1]

The spectrum of this star matches a stellar classification of A1 V,[3][4] which identifies it as an A-type main sequence star that is generating energy through the nuclear fusion of hydrogen at its core. An unusual abundance of the element europium demonstrates it to be a peculiar, or Ap star.[13] Most stars of this type are slow rotators,[14] but Gamma Trianguli Australis displays a very high rate of rotation with a projected rotational velocity of 199 km s−1.[4] It has an estimated age of 260 million years.[10]

This system 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.[8]

Modern legacy[edit]

γ TrA appears on the flag of Brazil, symbolising the state of Paraná.[15]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
  2. ^ a b c Wielen, R.; et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W
  3. ^ a b Levato, O. H. (August 1972), "Rotational Velocities and Spectral Types of Some A-Type Stars", Publications of the Astronomical Society of the Pacific, 84 (500): 584, Bibcode:1972PASP...84..584L, doi:10.1086/129336
  4. ^ a b c d Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224
  5. ^ a b Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99). Bibcode:1966CoLPL...4...99J.
  6. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  7. ^ a b c David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146.
  8. ^ a b Rhee, Joseph H.; et al. (May 2007), "Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs", The Astrophysical Journal, 660 (2): 1556–1571, arXiv:astro-ph/0609555, Bibcode:2007ApJ...660.1556R, doi:10.1086/509912
  9. ^ Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691.
  10. ^ a b Rieke, G. H.; et al. (February 2005), "Decay of Planetary Debris Disks", The Astrophysical Journal, 620 (2): 1010–1026, Bibcode:2005ApJ...620.1010R, CiteSeerX, doi:10.1086/426937
  11. ^ "gam TrA -- Variable Star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-02-04
  12. ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  13. ^ Sokolov, N. A. (June 1998), "Effective temperatures of AP stars", Astronomy and Astrophysics Supplement, 130: 215–222, Bibcode:1998A&AS..130..215S, doi:10.1051/aas:1998226
  14. ^ Abt, Helmut A.; Morrell, Nidia I. (July 1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", Astrophysical Journal Supplement, 99: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182
  15. ^ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website.