Astronomy:Epsilon1 Arae

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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 (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), Bibcode1966CoLPL...4...99J. 
  5. Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions, Astronomisches Rechen-Institut Heidelberg, 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, archived from the original on 2012-03-18,, 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