Theta Tauri

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θ Tauri
Hyades showing θ Tauri
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Taurus
θ1 Tauri
Right ascension 04h 28m 34.49603s[1]
Declination +15° 57′ 43.8494″[1]
Apparent magnitude (V) +3.84
θ2 Tauri
Right ascension 04h 28m 39.74070s[1]
Declination +15° 52′ 15.1745″[1]
Apparent magnitude (V) +3.35 - 3.42[2]
θ1 Tauri
Spectral type G9 III Fe-0.5[3]
θ2 Tauri
Spectral type A7 III[4]
Variable type δ Scuti[2]
θ1 Tauri
Parallax (π)21.4183 ± 0.3731 mas[5]
Distance152 ± 3 ly
(46.7 ± 0.8 pc)
Absolute magnitude (MV)+0.416[6]
θ2 Tauri
Parallax (π)20.8354 ± 0.3731 mas[7]
Distance157 ± 3 ly
(48.0 ± 0.9 pc)
Absolute magnitude (MV)+0.30/+1.44[8]
Period (P)5,997 days
Eccentricity (e)0.64
Semi-amplitude (K1)
8.39 km/s
Period (P)140.7302 days
Semi-major axis (a)18.91″
Eccentricity (e)0.7360
Inclination (i)47.8°
Semi-amplitude (K1)
32.95 km/s
Semi-amplitude (K2)
43.68 km/s
Mass2.86[10] M
Radius4.4[10] R
Luminosity59[8] L
Surface gravity (log g)3.6[10] cgs
Temperature7,800[10] K
Rotational velocity (v sin i)68.4[8] km/s
Mass2.16[10] M
Radius2.7[10] R
Luminosity21[8] L
Temperature7,800[8] K
Rotational velocity (v sin i)113[8] km/s
Age650[8] Myr
θ1 Tauri
Mass2.67[11] M
Radius10.55[11] R
Luminosity71[11] L
Surface gravity (log g)3.21[11] cgs
Temperature5,080[11] K
Metallicity [Fe/H]+0.14[11] dex
Rotational velocity (v sin i)1.40[11] km/s
Age510[11] Myr
Other designations
θ Tauri
θ1 Tauri: 77 Tauri, BD+15 631, HD 28307, HIP 20885, HR 1411, SAO 93955
θ2 Tauri: Chamukuy, 78 Tauri, BD+15 632, HD 28319, HIP 20894, HR 1412, SAO 93957
Database references
SIMBADθ1 Tauri
θ2 Tauri

Theta Tauri (θ Tauri, abbreviated Theta Tau, θ Tau) is a wide double star in the constellation of Taurus and a member of the Hyades open cluster.

θ Tauri is composed of two 3rd magnitude stars, designated Theta¹ Tauri (Theta Tauri B) and Theta² Tauri (Theta Tauri A). Theta² is brighter, hence the pair are sometimes referred to as Theta Tauri B and A, 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 152 ly (47 pc), while Theta² Tauri is at a distance of 157 light-years (48 parsecs). θ Tauri A and B are both spectroscopic binaries; the four components are designated Theta Tauri Aa (formally named Chamukuy /ˈɑːmki/), Ab, Ba, and Bb.


The θ Tauri pair, showing contrasting blue and yellow colors, in the Hyades cluster. In this image, θ1 Tauri is above in yellow, and θ2 Tauri is below in light blue.

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).[12]

In the mythology of the Maya peoples, Theta Tauri is known as Chamukuy, meaning a small bird in the Yucatec Maya language.[13] In 2016, the IAU organized a Working Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[15] 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.[16]

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.[17] Consequently, the Chinese name for Theta² Tauri itself is 畢宿六 (Bì Xiù liù), "the Sixth Star of Net".[18]


Theta Tauri B is the dimmer constituent. Its primary component, Theta Tauri Ba, is an orange K-type giant with an apparent magnitude of +3.84. The secondary, Theta Tauri Bb, 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.[19]

Theta Tauri A 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.[20] Its primary component, Theta Tauri Aa, is a white A-type giant. The secondary, Theta Tauri Ab, 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 van Leeuwen, F. (November 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. S2CID 18759600.
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  6. ^ 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.
  7. ^ Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  8. ^ a b c d e f g h Torres, K. B. V.; Lampens, P.; Frémat, Y.; Hensberge, H.; Lebreton, Y.; Škoda, P.; Guenther, E.; Schwope, A.; Heber, U. (2011). "Spectra disentangling applied to the Hyades binary θ2 Tauri AB: New orbit, orbital parallax and component properties". Astronomy and Astrophysics. 525: A50. arXiv:1010.5643. Bibcode:2011A&A...525A..50T. doi:10.1051/0004-6361/201015166. S2CID 55408682.
  9. ^ Mermilliod, J. -C; Andersen, J.; Latham, D. W.; Mayor, M. (2007). "Red giants in open clusters. XIII. Orbital elements of 156 spectroscopic binaries". Astronomy and Astrophysics. 473 (3): 829. Bibcode:2007A&A...473..829M. doi:10.1051/0004-6361:20078007.
  10. ^ a b c d e f Liakos, Alexios; Niarchos, Panagiotis (2017). "Catalogue and properties of δ Scuti stars in binaries". Monthly Notices of the Royal Astronomical Society. 465 (1): 1181. arXiv:1611.00200. Bibcode:2017MNRAS.465.1181L. doi:10.1093/mnras/stw2756.
  11. ^ a b c d e f g h Jofré, E.; Petrucci, R.; Saffe, C.; Saker, L.; de la Villarmois, E. Artur; Chavero, C.; Gómez, M.; Mauas, P. J. D.; Heber, U. (2015). "Stellar parameters and chemical abundances of 223 evolved stars with and without planets". Astronomy and Astrophysics. 574: A50. arXiv:1410.6422. Bibcode:2015A&A...574A..50J. doi:10.1051/0004-6361/201424474. S2CID 53666931.
  12. ^ 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].
  13. ^ Susan Milbrath (1 January 2010). Star Gods of the Maya: Astronomy in Art, Folklore, and Calendars. University of Texas Press. ISBN 978-0-292-77851-1.
  14. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  15. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  16. ^ "Naming Stars". Retrieved 16 December 2017.
  17. ^ 陳久金 (2005). 中國星座神話. 五南圖書出版股份有限公司. 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. ^ 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 (1): 167. Bibcode:1997ApJ...485..167T. doi:10.1086/304422.
  20. ^ 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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