Theta Tauri

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θ¹ Tauri
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Taurus
Right ascension 04h 28m 34.49603s[1]
Declination +15° 57′ 43.8494″[1]
Apparent magnitude (V) +3.84
Absolute magnitude (V)+0.416[2]
Distance154 ± 2[1] ly
(47.3 ± 0.6 pc)
Spectral typeK0 IIIb Fe-0.5
Other designations
Chamukuy, 77 Tau, BD+15 631, HD 28307, HIP 20885, HR 1411, SAO 93955.
θ² Tauri
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Taurus
Right ascension 04h 28m 39.74070s[1]
Declination +15° 52′ 15.1745″[1]
Apparent magnitude (V) +3.40
Absolute magnitude (V)+0.08[3]
Distance150 ± 3[1] ly
(46.1 ± 1.0 pc)
Spectral typeA7 III
Other designations
78 Tau, BD+15 632, HD 28319, HIP 20894, HR 1412, SAO 93957.

Theta Tauri (θ Tauri, abbreviated Tet Tau, θ Tau) is a double star in the constellation of Taurus and a member of the Hyades open cluster. It is composed of two 3rd magnitude stars, designated Theta¹ Tauri and Theta² Tauri, or alternatively Theta Tauri A and B, respectively. They are separated by 5.62 arcminutes (0.094°) on the sky. Based upon parallax measurements, Theta¹ Tauri is located at a distance of 154.4 ly (47.3 pc), while Theta² Tauri is at a distance of 150.4 light-years (46.1 parsecs).[1] As such, the two components are separated by about four light years and hence are unlikely to form a binary star system.

Both Theta Tauri A and B are spectroscopic binaries, whose four components are designated Theta Tauri Aa (also named Chamukuy[4]), Ab, Ba and Bb.


θ Tauri (Latinised to Theta Tauri) is the double star's Bayer designation; θ¹ Tauri and θ² Tauri those of its two constituents. The designations of the two constituents as Theta Tauri A and B, and those of the four components - Theta Tauri Aa, Ab, Ba and Bb - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[5]

In the mythology of the Maya peoples, Theta Tauri is known as Chamukuy, meaning a small bird in the Yucatec Maya language.[6] In 2016, the IAU organized a Working Group on Star Names (WGSN)[7] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[8] It approved the name Chamukuy for the component Theta Tauri Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[4]

In Chinese, 畢宿 (Bì Xiù), meaning Net, refers to an asterism consisting of Theta² Tauri, Epsilon Tauri (named Ain), Delta³ Tauri, Delta¹ Tauri, Gamma Tauri, Alpha Tauri (Aldebaran), 71 Tauri and Lambda Tauri.[9] Consequently, Theta² Tauri itself is known as 畢宿六 (Bì Xiù liù), "the Sixth Star of Net".[10]


Theta Tauri A is the dimmer constituent. Its primary component, Theta Tauri Aa, is an orange K-type giant with an apparent magnitude of +3.84. The secondary, Theta Tauri Ab, is of the 7th-magnitude. It has a mass of 1.31 M and orbits the primary every 16.26 years on a fairly eccentric (at 0.570) orbit.[11]

Theta Tauri B has a mean apparent magnitude of +3.40. It is classified as a Delta Scuti type variable star and its brightness varies from magnitude +3.35 to +3.42 with a period of 1.82 hours.[12] Its primary component, Theta Tauri Ba, is a white A-type giant. The secondary, Theta Tauri Bb, is of the 6th magnitude and is 0.005 arcseconds, or at least 2 AU, distant. It completes an orbit once every 141 days.


  1. ^ a b c d e f g van Leeuwen, F. (November 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. ^ Böhm-Vitense, Erika; et al. (December 2000), "Ultraviolet Emission Lines in BA and Non-BA Giants", The Astrophysical Journal, 545 (2): 992–999, Bibcode:2000ApJ...545..992B, doi:10.1086/317850. 
  3. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971Freely accessible, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015. 
  4. ^ a b "Naming Stars". Retrieved 16 December 2017. 
  5. ^ 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:1012.0707Freely accessible [astro-ph.SR]. 
  6. ^ Susan Milbrath: Star gods of the Maya: astronomy in art, folklore, and calendars on p. 253, University of Texas Press, Texas 1999, 2010.
  7. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. 
  8. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14. 
  9. ^ (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.
  10. ^ (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.
  11. ^ Torres, Guillermo; Stefanik, Robert P.; Latham, David W. (1997). "The Hyades Binaries θ1 Tauri and θ2Tauri: The Distance to the Cluster and the Mass‐Luminosity Relation". The Astrophysical Journal. 485: 167. Bibcode:1997ApJ...485..167T. doi:10.1086/304422. 
  12. ^ Solano, E.; Fernley, J. (April 1997), "Spectroscopic survey of delta Scuti stars. I. Rotation velocities and effective temperatures", Astronomy & Astrophysics Supplement Series, 122: 131–147, Bibcode:1997A&AS..122..131S, doi:10.1051/aas:1997329. 

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