Astronomy:Gamma Trianguli Australis

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Short description: Star in the constellation Triangulum Australe
Gamma Trianguli Australis
Location of γ Trianguli Australis (circled)
Observation data
Equinox J2000.0]] (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[1] mas/yr
Dec.: −31.187[1] mas/yr
Parallax (π)17.1809 ± 0.3327[1] mas
Distance190 ± 4 ly
(58 ± 1 pc)
Absolute magnitude (MV)−0.89[5]
Details[3]
Mass3.04 M☉
Radius6.5 or 7 R☉
Luminosity249[6] L☉
Surface gravity (log g)3.39[7] cgs
Temperature8,225 K
Rotational velocity (v sin i)199[8] km/s
Age350 Myr
Other designations
γ TrA, CD−68°1503, FK5 560, HD 135382, HIP 74946, HR 5671, SAO 253097[9]
Database references
SIMBADdata

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]

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 astronomical unit|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]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 Wielen, R. et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg (Astronomisches Rechen-Institut Heidelberg) 35 (35): 1, Bibcode: 1999VeARI..35....1W 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Waisberg, Idel; Klein, Ygal; Katz, Boaz (May 2024). "Hidden Companions to Intermediate-mass Stars. XIX. Spin–Orbit Misalignment and a 0.26M⊙, 1.8 au Companion in the Astrometric Binary Gamma Trianguli Australis*" (in en). Research Notes of the AAS 8 (5): 131. doi:10.3847/2515-5172/ad4a7b. ISSN 2515-5172. Bibcode: 2024RNAAS...8..131W. 
  4. ↑ 4.0 4.1 Johnson, H. L. et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory 4 (99): 99. Bibcode: 1966CoLPL...4...99J. 
  5. ↑ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A. 
  6. ↑ 6.0 6.1 Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics 537: A120, doi:10.1051/0004-6361/201117691, Bibcode: 2012A&A...537A.120Z. 
  7. ↑ 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, doi:10.1088/0004-637X/804/2/146, Bibcode: 2015ApJ...804..146D. 
  8. ↑ 8.0 8.1 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, doi:10.1051/0004-6361:20065224, Bibcode: 2007A&A...463..671R 
  9. ↑ "gam TrA -- Variable Star", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Gamma+Trianguli+Australis, retrieved 2012-02-04 
  10. ↑ Sokolov, N. A. (June 1998), "Effective temperatures of AP stars", Astronomy and Astrophysics Supplement 130 (2): 215–222, doi:10.1051/aas:1998226, Bibcode: 1998A&AS..130..215S 
  11. ↑ 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, doi:10.1086/192182, Bibcode: 1995ApJS...99..135A 
  12. ↑ "Sun Fact Sheet". https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html. 
  13. ↑ "The Colour of Stars". 6 March 2024. https://www.atnf.csiro.au/outreach/education/senior/astrophysics/photometry_colour.html. 
  14. ↑ Rhee, Joseph H. et al. (May 2007), "Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs", The Astrophysical Journal 660 (2): 1556–1571, doi:10.1086/509912, Bibcode: 2007ApJ...660.1556R 
  15. ↑ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website. https://flagspot.net/flags/br_astro.html. 



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