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Triangulum Australe

Coordinates: Sky map 16h 00m 00s, −65° 00′ 00″
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For the northern constellation, see Triangulum.
Triangulum Australe
Constellation
Triangulum Australe
List of stars in Triangulum Australe
AbbreviationTrA
GenitiveTrianguli Australis
Pronunciation/traɪˈæŋɡjʊləm ɒsˈtreɪliː/,
genitive /traɪˈæŋɡjʊlaɪ ɒˈstreɪl[invalid input: 'ɨ']s/
Symbolismthe Southern Triangle
Right ascension16
Declination−65
QuadrantSQ3
Area110 sq. deg. (83rd)
Main stars3
Bayer/Flamsteed
stars		10
Stars with planets1
Stars brighter than 3.00m3
Stars within 10.00 pc (32.62 ly)0
Brightest starα TrA (Atria) (1.91m)
Messier objectsNone
Meteor showersNone
Bordering
constellations		Norma
Ara
Circinus
Apus
Visible at latitudes between +25° and −90°.
Best visible at 21:00 (9 p.m.) during the month of July.

Triangulum Australe is a small constellation in the southern sky, created in the sixteenth century. Its name is Latin for 'the southern triangle', which distinguishes it from Triangulum in the northern sky. Its name derives from its three brightest stars which form an approximately equilateral triangle. Alpha Trianguli Australis, known as Atria, is a second magnitude orange giant and the brightest star in the constellation. Beta and Gamma Trianguli Australis are white main sequence stars and round out the triangle. Although the constellation lies in the Milky Way and contains many stars, deep sky objects are not prominent. Other notable features include the open cluster NGC 6025 and planetary nebula NGC 5979.

Characteristics

Triangulum Australe is a small constellation bordered by Norma to the North, Circinus to the west, Apus to the south and Ara to the east. It lies near the Pointers, with only Circinus in between. A roughly equilateral triangle, it is easily identifiable. It lies too far south in the celestial southern hemisphere to be visible from Europe,[1] yet is circumpolar from most of the southern hemisphere.[2] The recommended three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is 'TrA'.[3] The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 18 segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 14h 56.4m and 17h 13.5m , while the declination coordinates are between -60.26° and -70.51°.[4] Triangulum Australe culminates each year at 9 p.m. on 23 August.[5]

Notable features

See also: List of stars in Triangulum Australe

Nicolas Louis de Lacaille gave twelve stars Bayer designations of Alpha through to Lambda, with two close stars called Eta, while Lambda was later dropped due to its dimness.[6] The three brightest stars, Alpha, Beta and Gamma, make up an equilateral triangle. Readily identified by its orange hue,[1] Alpha Trianguli Australis is a bright giant star of spectral class K2 IIb-IIIa with an apparent magnitude of +1.91, which lies 424 light-years (130 parsecs) away and has an absolute magnitude of -3.68 and is 5500 times more luminous than our sun.[7] Beta Trianguli Australis is a double star, the primary being a F-type main-sequence star with a stellar classification of F1 V,[8] and an apparent magnitude of 2.85.[9] Lying only 40 light-years (12 parsecs) away, it has an absolute magnitude of 2.38.[10] The remaining member of the triangle is Gamma Trianguli Australis with an apparent magnitude of 2.87.[11] It is an A-type main sequence star of spectral class A1 V, which lies 180 light-years (55 parsecs) away.[10]

Located outside the triangle near Beta, Delta Trianguli Australis is the fourth brightest star at apparent magnitude +3.8, yet in reality is a much more powerful star that lies further away.[1] It is a yellow giant of spectral type G2Ib-II.[12] Lying halfway between Beta and Gamma, Epsilon Trianguli Australis is a double star. The primary component, Epsilon Trianguli Australis A, is an orange K-type sub-giant of spectral type K1.5III C with an apparent magnitude of +4.11V.[13] The companion, Epsilon Trianguli Australis B (or HD 138510), is a white A-type main sequence dwarf of spectral type A9IV/V C which has an apparent magnitude of +9.32v,[14]

Zeta Trianguli Australis appears as a star of apparent magnitude +4.91 and spectral class F9V, yet is actually a spectroscopic binary with a companion whose spectrum and identity are unknown yet likely to be a red dwarf. The pair orbit each other once every 13 days.[15] Iota Trianguli Australis shows itself to be composed of a yellow and a white star when seen though a 7.5 cm telescope.[16] HD 147018 is a sun-like star of apparent magnitude 8.3 and spectral type G9V,[12] which was found to have two exoplanets, HD 147018 b and HD 147018 c, in 2009.[17]

Triangulum Australe contains several cepheid variables, all of which are too faint to be seen with the naked eye:[18] R Trianguli Australis which ranges from apparent magnitude 6.4 to 6.9 over a period of 3.389 days, S Trianguli Australis ranges from apparent magnitude 6.1 to 6.8 over a period of 6.323 days, and U Trianguli Australis varies from 7.5 to 8.3 over 2.568 days.[2] All three are yellow-white giants of spectral type F7Ib/II,[19] F8II,[20] and F8Ib/II respectively.[21] RT Trianguli Australis is an unusual cepheid variable which shows strong absorption bands in C2, CH and CN, and has been classified as a carbon cepheid of spectral type R. It varies between magnitudes 9.2 and 9.97 over 1.95 days.[22] Lying nearby Gamma, X Trianguli Australis is a variable carbon star with an average magnitude of 5.63.[23] The 12th magnitude star EK Trianguli Australis is a dwarf nova of the SU Ursae Majoris type.[24]

Triangulum Australe lies within the Milky Way, so has many stars, yet is not well represented with deep sky objects—one open cluster and a few planetary nebulae and faint galaxies.[2] Its notable features include NGC 6025, an open cluster with about 30 stars ranging from 7th to 9th magnitude.[2] Lying 3 degrees north and 1 east of Beta Trianguli Australis, it lies about 2500 light years away and is about 11 light years in diameter. Its brightest star is MQ Trianguli Australis at apparent magnitude 7.1.[25] NGC 5979 is a planetary nebula of apparent magnitude 12.3, which has a blue-green hue at higher magnifications, while Henize 2-138 is a smaller planetary nebula of magnitude 11.0.[26] NGC 5938 is a remote spiral galaxy around 300 million light-years away. It is located 5' south of Epsilon Trianguli Australis.[27]

History

The invention of this constellation is obscure but can be attributed to 16th century seafarers. It was introduced in 1589 by Petrus Plancius on a 32½-cm diameter celestial globe published in Amsterdam by Jacob Floris van Langren,[28] where it was called Triangulus Antarcticus and was misplaced south of Argo Navis. His student Petrus Keyzer along with Houtman coined the name Den Zuyden Trianghel.[6] It was first depicted in a celestial atlas in the Uranometria of Johann Bayer in 1603.[29]

Lacaille portrayed the constellations of Norma, Circinus and Triangulum Australe as a set square and ruler, a compass, and a surveyor's level respectively in a set of draughtsman's instruments in his 1756 map of the southern stars.[30] Also depicting it as a surveyor’s level, German Johann Bode gave it the alternate name of Libella in his Uranographia.[28] German poet and author Philippus Caesius saw the three main stars as representing the Three Patriarchs, Abraham, Isaac and Jacob (with Atria as Abraham).[31]

References

  1. ^ a b c Moore, Patrick (2005). The Observer's Year: 366 Nights of the Universe. Springer. p. 116. ISBN 1852338849.
  2. ^ a b c d Inglis, Mike (2004). Astronomy of the Milky Way: Observer's Guide to the Southern Sky. Springer. p. 119. ISBN 1852337427.
  3. ^ Russell, Henry Norris (1922). "The new international symbols for the constellations". Popular Astronomy. 30: 469. Bibcode:1922PA.....30..469R.
  4. ^ "Triangulum Australe, constellation boundary" (Document). International Astronomical Union. {{cite document}}: Unknown parameter |accessdate= ignored (help); Unknown parameter |url= ignored (help); Unknown parameter |work= ignored (help)CS1 maint: postscript (link)
  5. ^ James, Andrew (7 February 2011). "'The '"Constellations : Part 2 Culmination Times"'". Southern Astronomical Delights. Sydney, New South Wales. Retrieved 10 September 2012.
  6. ^ a b Wagman, Morton (2003). Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg, VA: The McDonald & Woodward Publishing Company. pp. 303–04. ISBN 978-0-939923-78-6.
  7. ^ Ayres, Thomas R.; Brown, Alexander; Harper, Graham M. (2007), "α TrA Junior", The Astrophysical Journal, 658 (2): L107–L110, Bibcode:2007ApJ...658L.107A, doi:10.1086/514818 {{citation}}: Unknown parameter |month= ignored (help)
  8. ^ Gray, R. O.; et al. (2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637 {{citation}}: Unknown parameter |month= ignored (help)
  9. ^ Nicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Astronomy and Astrophysics Supplement Series. 34: 1–49. Bibcode:1978A&AS...34....1N. {{cite journal}}: Unknown parameter |month= ignored (help)
  10. ^ a b Schaaf, Fred (2008). The Brightest Stars: Discovering the Universe Through the Sky's Most Brilliant Stars. Hoboken, New Jersey: John Wiley and Sons. pp. 263–65. ISBN 047170410. {{cite book}}: Check |isbn= value: length (help)
  11. ^ Wielen, R.; et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions, Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W
  12. ^ a b "Delta Trianguli Australis". SIMBAD. Retrieved 7 June 2012. Cite error: The named reference "simbad" was defined multiple times with different content (see the help page).
  13. ^ "Epsilon Trianguli Australis". SIMBAD. Retrieved 7 June 2012.
  14. ^ "HD 138510". SIMBAD. Retrieved 7 June 2012.
  15. ^ Skuljan, Jovan (2004), "Accurate orbital parameters for the bright southern spectroscopic binary ζ Trianguli Australis – an interesting case of a near-circular orbit", Monthly Notices of the Royal Astronomical Society, 352: 975, Bibcode:2004MNRAS.352..975S, doi:10.1111/j.1365-2966.2004.07988.x
  16. ^ Hartung, Ernst Johannes (1984). Astronomical Objects for Southern Telescopes, with an Addendum for Northern Observatories: A Handbook for Amateur Observers. CUP Archive. p. 214. ISBN 0521318874.
  17. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1051/0004-6361/200912136, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1051/0004-6361/200912136 instead.
  18. ^ Klepešta, Josef (1974) [1969]. Constellations. Hamlyn. pp. 248–49. ISBN 0-600-00893-2. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  19. ^ "V* R TrA -- Classical Cepheid (delta Cep type)". SIMBAD. Retrieved 2 September 2012.
  20. ^ "V* S TrA -- Classical Cepheid (delta Cep type)". SIMBAD. Retrieved 2 September 2012.
  21. ^ "V* U TrA -- Cepheid variable Star". SIMBAD. Retrieved 2 September 2012.
  22. ^ Wallerstein, George; Matt, Sean; Gonzalez, Guillermo (2000). "The carbon Cepheid RT Trianguli Australis: additional evidence of triple-α and CNO cycling". Monthly Notices of the Royal Astronomical Society. 311 (2): 414–22. Bibcode:2000MNRAS.311..414W. doi:10.1046/j.1365-8711.2000.03064.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. ^ "V* X TrA -- Carbon Star". SIMBAD. Retrieved 9 September 2012.
  24. ^ "A superoutburst of the dwarf nova EK Trianguli Australis". Monthly Notices of the Royal Astronomical Society. 216: 335–52. September 15, 1985. Bibcode:1985MNRAS.216..335H. ISSN 0035-8711. {{cite journal}}: Cite uses deprecated parameter |authors= (help)
  25. ^ Mobberley, Martin (2009). The Caldwell Objects and How to Observe Them. Springer. p. 198. ISBN 1441903259.
  26. ^ Griffiths, Martin (2012). Planetary Nebulae and How to Observe Them. Springer. p. 262. ISBN 1461417813.
  27. ^ Polakis, Tom (2001). "Ara, Triangulum and Apus: A spectacular myriad of deep-sky objects fills this southern trio". Astronomy. 29 (7): 80–84. ISSN 0091-6358.
  28. ^ a b Ridpath, Ian. "Triangulum Australe". Star Tales. Retrieved 7 June 2012.
  29. ^ Moore, Patrick; Tirion, Wil (1997). Cambridge Guide to Stars and Planets. Cambridge, United Kingdom: Cambridge University Press. ISBN 978-0-521-58582-8.
  30. ^ Ridpath, Ian. "Lacaille's grouping of Norma, Circinus, and Triangulum Australe". Star Tales. Retrieved 7 June 2012.
  31. ^ Motz, Lloyd (1991). The Constellations: An Enthusiast's Guide to the Night Sky. London, United Kingdom: Aurum Press. p. 387. ISBN 1-85410-088-2. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
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