Zeta Tauri

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Zeta Tauri
Diagram showing star positions and boundaries of the Taurus constellation and its surroundings
Cercle rouge 100%.svg

Location of ζ Tauri (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Taurus
Right ascension 05h 37m 38.68542s[1]
Declination +21° 08′ 33.1588″[1]
Apparent magnitude (V) 3.010[2]
Characteristics
Spectral type B2 IIIpe[3]
U−B color index –0.749[2]
B−V color index –0.164[2]
Astrometry
Radial velocity (Rv) +20[4] km/s
Proper motion (μ) RA: +1.78[1] mas/yr
Dec.: –20.07[1] mas/yr
Parallax (π) 7.33 ± 0.82[1] mas
Distance approx. 440 ly
(approx. 140 pc)
Orbit[3]
Period (P) 132.987 days
Semi-major axis (a) 1.17 AU
Eccentricity (e) 0.0 (assumed)
Inclination (i) 92.8°
Longitude of the node (Ω) –58.0°
Periastron epoch (T) 2,447,025.6 HJD
Argument of periastron (ω)
(secondary)
0.0 (assumed)°
Semi-amplitude (K1)
(primary)
7.43 km/s
Details
ζ Tau A
Mass 11.2[3] M
Radius 5.5[3] R
Luminosity 4,169[5] L
Temperature 15,500[5] K
Rotational velocity (v sin i) 125[6] km/s
Age 22.5 ± 2.6[7] Myr
ζ Tau B
Mass 0.94[3] M
Other designations
123 Tauri, HR 1910, HD 37202, BD+21 908, FK5 211, HIP 26451, SAO 77336, GC 6985.[8]

Zeta Tauri (ζ Tau, ζ Tauri) is a binary star in the zodiac constellation Taurus, the Bull. It has an apparent visual magnitude of 3.0,[2] which is bright enough to be seen with the naked eye. Parallax measurements place it at a distance of roughly 440 light-years from the Earth.[1]

In Chinese astronomy, Zeta Tauri is called 天關, Pinyin: Tiānguān, meaning Celestial Gate, an asterism within the Net (畢宿 Bì Xiù) mansion (see also: Chinese constellation).[9] 天關 (Tiānguān) has also been transliterated as Tien Kwan. Technically, Tiānguān refers not just to Zeta Tauri but to an asterism of which Zeta Tauri is the main star, alongside 113 Tau, 126 Tau, 128 Tau, 129 Tau, 130 Tau and 127 Tau (see Taurus (Chinese astronomy)).[10]

Properties[edit]

This is a single-lined spectroscopic binary system, which means the two components are orbiting so close to each other that they can not be resolved with a telescope. Instead, the orbital motion of the primary component is indicated by Doppler effect shifts in the absorption lines in its spectrum. The two components are separated by an estimated distance of about 1.17 Astronomical Units, or 117% of the distance from the Earth to the Sun. They are following circular orbits with a period of nearly 133 days.[3]

Compared to the Sun, the primary is an enormous star with more than 11 times the mass and 5–6 times the radius.[3] It is rotating rapidly with a projected rotational velocity of 125 km s–1.[6] The companion has about 94% the mass of the Sun, although it is unknown whether this is a main sequence star, a neutron star, or a white dwarf. If it is a main sequence star, then the mass indicates it may have a stellar classification of G4.[3]

The spectrum of the primary component has a stellar classification of B2 IIIpe.[3] A luminosity class of 'III' indicates this is a giant star that has exhausted the hydrogen at its core and evolved away from the main sequence. The 'e' suffix is used for stars that show emission lines in their spectrum. For Be stars such as this, the emission lines are produced by a rotating circumstellar disk of gas, made of material that has been ejected from the star's outer envelope. An oscillatory pattern in this spectrum is being caused by a single-armed spiral density wave in the disk. The disk may be precessing from the gravitational influence of the secondary component.[3]

References[edit]

  1. ^ a b c d e f 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 
  2. ^ a b c d Harmanec, P. et al., "Photoelectric photometry at the Hvar Observatory. IV - A study of UBV variations of a group of bright northern Be stars", Bulletin of the Astronomical Institutes of Czechoslovakia, Bulletin 31 (3): 144–159, Bibcode:1980BAICz..31..144H 
  3. ^ a b c d e f g h i j Schaefer, G. H. et al. (December 2010), "Multi-epoch Near-infrared Interferometry of the Spatially Resolved Disk around the Be Star ζ Tau", The Astronomical Journal 140 (6): 1838–1849, arXiv:1009.5425, Bibcode:2010AJ....140.1838S, doi:10.1088/0004-6256/140/6/1838 
  4. ^ Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E 
  5. ^ a b Balona, L. A.; Dziembowski, W. A. (October 1999), "Excitation and visibility of high-degree modes in stars", Monthly Notices of the Royal Astronomical Society 309 (1): 221–232, Bibcode:1999MNRAS.309..221B, doi:10.1046/j.1365-8711.1999.02821.x 
  6. ^ a b Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational velocities of B Stars", The Astrophysical Journal 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590 
  7. ^ Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x 
  8. ^ "zet Tau -- Be Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-01-20 
  9. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 24 日
  10. ^ Richard Hinckley Allen: Star Names — Their Lore and Meaning: Taurus