Tau2 Eridani

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τ² Eridani
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Eridanus
Right ascension 02h 51m 02.32186s[1]
Declination −21° 00′ 14.4654″[1]
Apparent magnitude (V) 4.78[2]
Spectral type K0 III[3]
U−B color index +0.63[2]
B−V color index +0.92[2]
Radial velocity (Rv)−5.9[4] km/s
Proper motion (μ) RA: −38.52[1] mas/yr
Dec.: −16.05[1] mas/yr
Parallax (π)17.45 ± 0.20[1] mas
Distance187 ± 2 ly
(57.3 ± 0.7 pc)
Absolute magnitude (MV)1.008[5]
Mass2.40 M
Radius8.12 R
Luminosity42.7 L
Surface gravity (log g)2.95 cgs
Temperature5,049 K
Metallicity [Fe/H]0.08 dex
Rotational velocity (v sin i)1.11 km/s
Age660 Myr
Other designations
Angetenar, τ² Eridani, 2 Eri, BD−21° 509, HD 17824, HIP 13288, HR 850, SAO 168094.[6]
Database references

Tau² Eridani (τ² Eridani, abbreviated Tau² Eri, τ² Eri), also named Angetenar,[7] is a star in the constellation of Eridanus. It is visible to the naked eye with an apparent visual magnitude of 4.78.[2] The distance to this star, as determined via the parallax method, is around 187 light-years.


τ² Eridani (Latinised to Tau² Eridani) is the system's Bayer designation. It is one of a series of stars that share the Bayer designation Tau Eridani.

It bore the traditional name Angetenar, derived from the Arabic Al Ḥināyat al Nahr, 'the Bend in the River', near which it lies.[8] In 2016, the IAU organized a Working Group on Star Names (WGSN)[9] to catalog and standardize proper names for stars. The WGSN approved the name Angetenar for this star on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.[7]

In Chinese, 天苑 (Tiān Yuàn), meaning Celestial Meadows, refers to an asterism consisting of Tau² Eridani, Gamma Eridani, Pi Eridani, Delta Eridani, Epsilon Eridani, Zeta Eridani, Eta Eridani, Pi Ceti, Tau¹ Eridani, Tau³ Eridani, Tau⁴ Eridani, Tau⁵ Eridani, Tau⁶ Eridani, Tau⁷ Eridani, Tau⁸ Eridani and Tau⁹ Eridani.[10] Consequently, Tau² Eridani itself is known as 天苑九 (Tiān Yuàn jiǔ, English: the Ninth Star of Celestial Meadows.)[11]


Tau² Eridani is an evolved K-type giant star with a stellar classification of K0 III.[3] It is a red clump giant on the horizontal branch of the Hertzsprung–Russell diagram, indicating that is it now generating energy through the thermonuclear fusion of helium at its core.[5]

Around 660 million years old, Tau² Eridani has 2.4 times the mass of the Sun and has expanded to over 8 times the solar radius. It shines with nearly 43 times the Sun's luminosity from an outer atmosphere that has an effective temperature of 5,049 K.[4]

It is a member of the Galactic thin disk population.[4]


  1. ^ a b c d e van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. ^ a b c d Mermilliod, J.-C. (1986), Compilation of Eggen's UBV data, transformed to UBV (unpublished), SIMBAD, Bibcode:1986EgUBV........0M.
  3. ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H.
  4. ^ a b c d Jofré, E.; et al. (2015), "Stellar parameters and chemical abundances of 223 evolved stars with and without planets", Astronomy & Astrophysics, 574, arXiv:1410.6422, Bibcode:2015A&A...574A..50J, doi:10.1051/0004-6361/201424474, A50.
  5. ^ a b Liu, Y. J.; et al. (2007), "The abundances of nearby red clump giants", Monthly Notices of the Royal Astronomical Society, 382 (2): 553–66, Bibcode:2007MNRAS.382..553L, doi:10.1111/j.1365-2966.2007.11852.x.
  6. ^ "* tau02 Eri". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-10-13.
  7. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  8. ^ Allen, Richard Hinckley (1963) [1899]. Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 220. ISBN 0-486-21079-0.
  9. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  10. ^ (in 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.
  11. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2010-08-11 at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.