Epoch J2000.0 Equinox J2000.0
|Right ascension||04h 28m 34.49603s|
|Declination||+15° 57′ 43.8494″|
|Apparent magnitude (V)||+3.84|
|Absolute magnitude (V)||+0.416|
|Distance||154 ± 2 ly|
(47.3 ± 0.6 pc)
|Spectral type||K0 IIIb Fe-0.5|
Epoch J2000.0 Equinox J2000.0
|Right ascension||04h 28m 39.74070s|
|Declination||+15° 52′ 15.1745″|
|Apparent magnitude (V)||+3.40|
|Absolute magnitude (V)||+0.08|
|Distance||150 ± 3 ly|
(46.1 ± 1.0 pc)
|Spectral type||A7 III|
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). As such, the two components are separated by about four light years and hence are unlikely to form a binary star system.
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).
In the mythology of the Maya peoples, Theta Tauri is known as Chamukuy, meaning a small bird in the Yucatec Maya language. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. 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.
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. Consequently, Theta² Tauri itself is known as 畢宿六 (Bì Xiù liù), "the Sixth Star of Net".
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.
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. 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.
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