Tau2 Eridani

From Wikipedia, the free encyclopedia
Jump to: navigation, search
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
Distance 187 ± 2 ly
(57.3 ± 0.7 pc)
Absolute magnitude (MV) 1.008[5]
Mass 2.40 M
Radius 8.12 R
Luminosity 42.7 L
Surface gravity (log g) 2.95 cgs
Temperature 5,049 K
Metallicity [Fe/H] 0.08 dex
Rotational velocity (v sin i) 1.11 km/s
Age 660 Myr
Other designations
Angetenar,[citation needed] τ2 Eridani, 2 Eri, BD−21° 509, HD 17824, HIP 13288, HR 850, SAO 168094.[6]
Database references

Tau2 Eridani2 Eri, 2 Eridani) is a star in the constellation Eridanus. It is one of a series of stars that share the Bayer designation Tau Eridani. The traditional name for this star is Angetenar, meaning "bend of the river" in Arabic. It is visible to the naked eye with an apparent visual magnitude of 4.78.[2] The distance to τ2 Eri, as determined via the parallax method, is around 187 light years.

In Chinese, 天苑 (Tiān Yuàn), meaning Celestial Meadows, refers to an asterism consisting of τ2 Eridani, γ Eridani, π Eridani, δ Eridani, ε Eridani, ζ Eridani, η Eridani, π Ceti, τ1 Eridani, τ3 Eridani, τ4 Eridani, τ5 Eridani, τ6 Eridani, τ7 Eridani, τ8 Eridani and τ9 Eridani.[7] Consequently, τ2 Eridani itself is known as 天苑九 (Tiān Yuàn jiǔ, English: the Ninth Star of Celestial Meadows.)[8]

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

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]


  1. ^ a b c d e van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, 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:1988MSS...C04....0H. 
  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:1410.6422Freely accessible, 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 -- Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2016-10-13. 
  7. ^ (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.
  8. ^ (in 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.