Gamma Tauri


γ Tauri
Taurus constellation map.svg
Red circle.svg
Location of γ Tauri (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Taurus
Right ascension 04h 19m 47.6037s[1]
Declination +15° 37′ 39.512″[1]
Apparent magnitude (V) 3.654[2]
Spectral type G8III[3]
U−B color index +0.84[4]
B−V color index +0.99[4]
Radial velocity (Rv)38.7 ± 0.9[5] km/s
Proper motion (μ) RA: +115.29[1] mas/yr
Dec.: -23.86[1] mas/yr
Parallax (π)21.17 ± 1.17[1] mas
Distance154 ± 9 ly
(47 ± 3 pc)
Absolute magnitude (MV)0.22[3]
Mass2.70 ± 0.13[6] M
Radius13.4 ± 0.2[7] R
Luminosity85[3] L
Surface gravity (log g)2.58-2.61[7] cgs
Temperature4,844 ± 47[7] K
Metallicity [Fe/H]+0.11[8] dex
Rotation253 days[9]
Rotational velocity (v sin i)4[10] km/s
Age430–530[3][6] Myr
Other designations
Prima Hyadum, Hyadum I,[11] 54 Tauri, BD+15°612, FK5 159, HD 27371, HIP 20205, HR 1346, SAO 93868, GC 5226, WDS 04198+1538[2]
Database references

Gamma Tauri (γ Tauri, abbreviated Gamma Tau, γ Tau) is either a solitary, binary or double star (the Washington Double Star Catalog notes it as a "Dubious Double" or "Bogus Binary"[12]) that marks the tip of the "V" in the constellation of Taurus. It is a member of, and located within about 2.5 parsecs of the center of, the Hyades star cluster, the nearest open cluster to the Sun. Based upon parallax measurements, Gamma Tauri is approximately 154 light-years from the Sun.

Considered as a pair of stars, the two components are designated Gamma Tauri A (officially named Prima Hyadum /ˌprmə ˈhədəm/, the traditional name for the system)[13] and B.


γ Tauri (Latinised to Gamma Tauri) is the system's Bayer designation. The designations of the two potential components as Gamma Tauri A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[14]

Gamma Tauri bore the traditional name Hyadum I,[11] which is Latin for "First of the Hyades". In 2016, the IAU organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[16] It approved the name Prima Hyadum for the component Gamma Tauri A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[13]

In Chinese, 畢宿 (Bì Xiù), meaning Net, refers to an asterism consisting of Gamma Tauri, Epsilon Tauri, Delta³ Tauri, Delta¹ Tauri, Alpha Tauri (Aldebaran), 71 Tauri and Lambda Tauri.[17] Consequently, the Chinese name for γ Tauri itself is 畢宿四 (Bì Xiù sì), "the Fourth Star of Net".[18]


Gamma Tauri presents as a spectral class G8 or K0[2][3] giant star with an apparent magnitude of +3.65. This star has passed through the main sequence phase is now a red clump giant, meaning it is using nuclear fusion of helium at its core to provide energy.[19] Age estimates for Gamma Tauri range from 430 million[3] to 530 million years.[6] By comparison, the age of the Hyades cluster is about 625 million years with an error margin of 50 million years.[6]

The angular diameter of this star has been measured using the CHARA array to 2% accuracy. After correcting for limb darkening, this gives the stellar radius as 13.4 times the radius of the Sun.[7] The star is radiating about 85 times the luminosity of the Sun[3] and has 2.7 times the Sun's mass.[6] With its large size and low projected rotational velocity of 4 km s−1,[10] it takes about 253 days to complete a rotation.[9]


  1. ^ a b c d e Perryman, M. A. C.; et al. (1997), "The Hipparcos Catalogue", Astronomy & Astrophysics, 323: L49–L52, Bibcode:1997A&A...323L..49P
  2. ^ a b c "NSV 1553 - Variable Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2009-09-22.
  3. ^ a b c d e f g Takeda, Yoichi; Sato, Bun'ei; Murata, Daisuke (August 2008). "Stellar Parameters and Elemental Abundances of Late-G Giants". Publications of the Astronomical Society of Japan. 60 (4): 781–802. arXiv:0805.2434. Bibcode:2008PASJ...60..781T. doi:10.1093/pasj/60.4.781. S2CID 16258166.
  4. ^ a b Johnson, H. L.; Morgan, W. W. (1953). "Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas". Astrophysical Journal. 117: 313–352. Bibcode:1953ApJ...117..313J. doi:10.1086/145697.
  5. ^ Evans, D. S. (June 20–24, 1966). "The Revision of the General Catalogue of Radial Velocities". In Batten, Alan Henry; Heard, John Frederick (eds.). Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30. University of Toronto: International Astronomical Union. Bibcode:1967IAUS...30...57E.
  6. ^ a b c d e da Silva, L.; et al. (November 2006). "Basic physical parameters of a selected sample of evolved stars". Astronomy and Astrophysics. 458 (2): 609–623. arXiv:astro-ph/0608160. Bibcode:2006A&A...458..609D. doi:10.1051/0004-6361:20065105. S2CID 9341088.
  7. ^ a b c d Boyajian, Tabetha S.; et al. (February 2009). "Angular Diameters of the Hyades Giants Measured with the CHARA Array". The Astrophysical Journal. 691 (2): 1243–1247. arXiv:0810.2238. Bibcode:2009ApJ...691.1243B. doi:10.1088/0004-637X/691/2/1243. S2CID 17092177.
  8. ^ Soubiran, C.; Bienaymé, O.; Mishenina, T. V.; Kovtyukh, V. V. (March 2008). "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants". Astronomy and Astrophysics. 480 (1): 91–101. arXiv:0712.1370. Bibcode:2008A&A...480...91S. doi:10.1051/0004-6361:20078788. S2CID 16602121.
  9. ^ a b 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, Bibcode:2004A&A...421..241S, doi:10.1051/0004-6361:20041042-1
  10. ^ a b Bernacca, P. L.; Perinotto, M. (1970). "A catalogue of stellar rotational velocities". Contributi Osservatorio Astronomico di Padova in Asiago. 239 (1). Bibcode:1970CoAsi.239....1B.
  11. ^ a b Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 390. ISBN 0-486-21079-0.
  12. ^ "Washington Double Star Catalog". United States Naval Observatory. Archived from the original on 14 February 2011. Retrieved 2 January 2018.
  13. ^ a b "Naming Stars". Retrieved 16 December 2017.
  14. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  15. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  16. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  17. ^ (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.
  18. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  19. ^ de Bruijne, J. H. J.; Hoogerwerf, R.; de Zeeuw, P. T. (February 2001). "A Hipparcos study of the Hyades open cluster. Improved colour-absolute magnitude and Hertzsprung-Russell diagrams". Astronomy and Astrophysics. 367 (1): 111–147. arXiv:astro-ph/0011565. Bibcode:2001A&A...367..111D. doi:10.1051/0004-6361:20000410. S2CID 55224801.