Astronomy:Epsilon1 Arae

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Short description: Star in the constellation Ara

Epsilon1 Arae
Diagram showing star positions and boundaries of the Ara constellation and its surroundings
Cercle rouge 100%.svg
The location of ε1 Arae (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Ara
Right ascension  16h 59m 35.04880s[1]
Declination –53° 09′ 37.5713″[1]
Apparent magnitude (V) +4.068[2]
Spectral type K3 III[3]
U−B color index +1.71[4]
B−V color index +1.45[4]
Radial velocity (Rv)+23.1[5] km/s
Proper motion (μ) RA: +2.16[1] mas/yr
Dec.: +22.04[1] mas/yr
Parallax (π)9.04 ± 0.27[1] mas
Distance360 ± 10 ly
(111 ± 3 pc)
Absolute magnitude (MV)–0.79 ± 0.16[6]
Mass1.74 ± 0.24[7] M
Radius33.7 ± 3.4[7] R
Surface gravity (log g)1.80[2] cgs
Temperature4,176[2] K
Metallicity [Fe/H]0.08 ± 0.05[2] dex
Age1.70 ± 0.57[7] Gyr
Other designations
CPD–52° 10372, FK5 632, HD 152980, HIP 83153, HR 6295, SAO 244331.[8]
Database references

Epsilon1 Arae1 Ara, ε1 Arae) is the Bayer designation for a star in the constellation Ara, the Altar. It is visible to the naked eye with an apparent visual magnitude of +4.1[2] Based upon an annual parallax shift of 9.04 mas,[1] this star is around 360 light-years (110 parsecs) distant from the Earth.

ε1 Arae is an evolved giant star[7] with a stellar classification of K3 III.[3] It is around 74% more massive than the Sun. At an age of about 1.7 billion years, the outer envelope of the star has expanded to almost 34 times the Sun's radius.[7] It is radiating energy into space at an effective temperature of 4,176 K,[2] giving it the orange-hued glow of a K-type star.[9]

ε1 Arae was known as 龜一(spelled as "Guī yī", meaning: "the 1st (star) of Guī") in traditional Chinese astronomy.[10][11] Allen erroneously called it Tso Kang (左更).[12] He probably confused the constellation "Ara" with "Ari", as Tso Kang is actually in Aries.[10][11]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode2007A&A...474..653V. 
  2. 2.0 2.1 2.2 2.3 2.4 2.5 Soubiran, C.; Le Campion, J.-F.; Cayrel de Strobel, G.; Caillo, A. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics 515: A111, doi:10.1051/0004-6361/201014247, Bibcode2010A&A...515A.111S. 
  3. 3.0 3.1 Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 2, Ann Arbor: Dept. of Astronomy, University of Michigan, 
  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, Bibcode1966CoLPL...4...99J. 
  5. 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, Bibcode1999VeARI..35....1W. 
  6. Setiawan, J. et al. (July 2004), "Precise radial velocity measurements of G and K giants. Multiple systems and variability trend along the Red Giant Branch", Astronomy and Astrophysics 421: 241–254, doi:10.1051/0004-6361:20041042-1, Bibcode2004A&A...421..241S. 
  7. 7.0 7.1 7.2 7.3 7.4 da Silva, L. et al. (November 2006), "Basic physical parameters of a selected sample of evolved stars", Astronomy and Astrophysics 458 (2): 609–623, doi:10.1051/0004-6361:20065105, Bibcode2006A&A...458..609D. 
  8. "eps01 Ara". SIMBAD. Centre de données astronomiques de Strasbourg. 
  9. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004,, retrieved 2012-07-21. 
  10. 10.0 10.1 Chevalier, S., and Tsuchihashi, P., (1911): "Catalogue d'Étoiles fixes, observés a Pekin sous l'Empereur Kien Long (Qianlong (Chien-Lung)), XVIIIe siecle", Annales de l'Observatoire Astronomique de Zô-Sé.
  11. 11.0 11.1 伊世同 (Yi Shi Tong) (1981): 『中西対照恒星図表』科学出版社.(in Chinese)
  12. Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc., p. 64, ISBN 0-486-21079-0, 

Further reading

  • 大崎正次 (1987): 「中国の星座・星名の同定一覧表」『中国の星座の歴史』 雄山閣出版, pp. 312, 326.(in Japanese)

External links