Alpha Trianguli Australis
 Location of α Trianguli Australis (circled) |
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| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Triangulum Australe |
| Right ascension | 16h 48m 39.89508s[1] |
| Declination | –69° 01′ 39.7626″[1] |
| Apparent magnitude (V) | 1.91[2] |
| Characteristics | |
| Spectral type | K2 IIb-IIIa[3] |
| U−B color index | +1.56[4] |
| B−V color index | +1.44[4] |
| Astrometry | |
| Radial velocity (Rv) | –3.3[2] km/s |
| Proper motion (μ) | RA: 17.99[1] mas/yr Dec.: –31.58[1] mas/yr |
| Parallax (π) | 8.35 ± 0.15[1] mas |
| Distance | 391 ± 7 ly (120 ± 2 pc) |
| Absolute magnitude (MV) | –3.68[5] |
| Details | |
| Mass | 7[3] M☉ |
| Luminosity | 5,500[5] L☉ |
| Surface gravity (log g) | 1.5[3] |
| Temperature | 4,150[3] K |
| Metallicity [Fe/H] | –0.06[3] dex |
| Age | 4.8 × 107[3] years |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Trianguli Australis (α TrA, α Trianguli Australis) is the brightest star in the southern circumpolar constellation Triangulum Australe, forming an apex of a triangle with Beta and Gamma Trianguli Australis that gives the constellation its name (Latin for southern triangle). This star has the traditional name Atria, which is merely a contraction of its Bayer designation.[7] 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.[1] 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.[3] 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,[3] which gives it the characteristic orange hue of a K-type star.[8]
There is evidence that Atria may be a binary star. It displays unusual properties for a star of its class, including stellar flares and a higher than normal emission of X-rays. These can be explained by a young, magnetically active companion with a stellar classification of about G0 V. Such a star would have a mass similar to the Sun, with an orbital period of at least 130 years. Young, G-type stars have a high temperature corona and frequently emit flares causing sudden increases in luminosity. The pair may be separated by about 50 Astronomical Units.[5]
[edit] In culture
Atria appears on the flag of Brazil, symbolizing the state of Rio Grande do Sul.[9]
[edit] References
- ^ a b c d e f van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
- ^ a b 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
- ^ a b c d e f g h Kovacs, N. (April 1983), "Model-atmosphere analysis of high-dispersion spectra of four red giants and supergiants", Astronomy and Astrophysics 120 (1): 21–35, Bibcode 1983A&A...120...21K
- ^ 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.
- ^ a b c Ayres, Thomas R.; Brown, Alexander; Harper, Graham M. (April 2007), "α TrA Junior", The Astrophysical Journal 658 (2): L107–L110, Bibcode 2007ApJ...658L.107A, doi:10.1086/514818
- ^ "alf TrA -- Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Alpha+Trianguli+Australis, retrieved 2011-12-26
- ^ Ridpath, Ian (1989), Star tales, James Clarke & Co., p. 125, ISBN 0718826957, http://books.google.com/books?id=gFrdcTdeVaEC&pg=RA1-PA12
- ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16
- ^ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website. http://www.fotw.net/flags/br_astro.html. Retrieved 2011-12-26.
[edit] External links
- Kaler, James B., "ATRIA (Alpha Trianguli Australis)", Stars (University of Illinois), http://www.astro.uiuc.edu/~kaler/sow/atria.html, retrieved 2011-12-26
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