Alpha Coronae Australis

α Coronae Australis
Diagram showing star positions and boundaries of the Corona Australis constellation and its surroundings


Location of α CrA (circled)

Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Corona Australis
Right ascension 19h 09m 28.34097s[1]
Declination –37° 54′ 16.1022″[1]
Apparent magnitude (V) 4.102[2]
Characteristics
Spectral type A2Va[3]
U−B color index +0.06[3]
B−V color index +0.04[3]
Astrometry
Radial velocity (Rv)−18.4[3] km/s
Proper motion (μ) RA: 84.87[3] mas/yr
Dec.: −95.99[3] mas/yr
Parallax (π)26.02 ± 0.25[1] mas
Distance125 ± 1 ly
(38.4 ± 0.4 pc)
Absolute magnitude (MV)1.11[4]
Details
Mass2.3[5] M☉
Radius2.3[5] R☉
Luminosity31[5] L☉
Temperature9,100[5] K
Rotational velocity (v sin i)195[6] km/s
Age254[2] Myr
Other designations
Alphekka Meridiana, α CrA, HR 7254, HD 178253, FK5 718, HIP 94114, SAO 210990, GC 26360, IRAS 19060-3759, 2MASS J19092834-3754157
Database references
SIMBADdata

Alpha Coronae Australis (α CrA, α Coronae Australis) is a star in the constellation Corona Australis. It is the only star in the constellation with a proper name, Alphekka Meridiana (Alphekka South), after the brightest star in Corona Borealis, Alphecca. In Chinese astronomy, it is known as 鱉六 (the Sixth Star of the River Turtle). It is a Class A star like Vega, rotating extremely fast on its axis, close to its breakup velocity.

Properties

Alpha Coronae Australis belongs to the spectral class A2Va and has apparent magnitude +4.10.[3] Located about 125 light years from Earth, the star's mass and radius are estimated at 2.3 times solar. With an effective temperature of roughly 9,100 K, the star radiates a total luminosity of about 31 times solar.[5] This star is roughly 254 million years old.[2] A rapidly rotating star, it spins at almost 200 km per second at the equator, making a complete revolution in approximately 14 hours.[6] Like the star Vega, it has excess infrared radiation, which indicates it may be ringed by a disk of dust.[5]

Etymology

The name Alphecca or Alphekka is Arabic, short for نير الفكّة nayyir al-fakka "the bright (star) of the broken (ring of stars)".[7]

In Chinese, 鱉 (Biē), meaning River Turtle, refers to an asterism consisting of α Coronae Australis, α Telescopii, η1Coronae Australis, ζ Coronae Australis, δ Coronae Australis, β Coronae Australis, γ Coronae Australis, ε Coronae Australis, HD 175362, κ2 Coronae Australis and θ Coronae Australis.[8] Consequently, α Coronae Australis itself is known as 鱉六 (Biēliù, English: the Sixth Star of River Turtle.).[9]

See also

References

  1. ↑ 1.0 1.1 1.2 van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction" (PDF). Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Retrieved 2012-08-28.
  2. ↑ 2.0 2.1 2.2 Song, Inseok et al. (February 2001), "Ages of A-Type Vega-like Stars from uvbyβ Photometry", The Astrophysical Journal 546 (1): 352–357, arXiv:astro-ph/0010102, Bibcode:2001ApJ...546..352S, doi:10.1086/318269
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 "SIMBAD query result:alf CrA -- Star". Centre de Données astronomiques de Strasbourg. Retrieved 2012-09-02.
  4. ↑ "α Coronae Australis (star)". Wolfram Alpha. Retrieved 2012-09-02.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Kaler, James B. "ALFECCA MERIDIANA (Alpha Coronae Australis)". Stars. University of Illinois. Retrieved 2012-09-02.
  6. ↑ 6.0 6.1 Royer, F.; Zorec, J.; Gómez, A. E. (February 2007). "Rotational velocities of A-type stars. III. Velocity distributions" (PDF) 463 (2). Astronomy and Astrophysics. pp. 671–682. arXiv:astro-ph/0610785. Bibcode:2007A&A...463..671R. doi:10.1051/0004-6361:20065224.
  7. ↑ Allen, Richard Hinckley, (1963) [1899]. Star Names: Their Lore and Meaning (rep. ed.). New York, NY: Dover Publications Inc. pp. 172–73. ISBN 0-486-21079-0.
  8. ↑ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  9. ↑ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.