Zeta Tauri
A binary star in Taurus, visible to the naked eye.
Zeta Tauri is a binary star system in the constellation Taurus, the Bull. Its apparent magnitude of about 3.0 makes it visible without a telescope. Located roughly 440 light-years away, it is also known as Tianguan. Because it lies near the ecliptic, the Moon can occasionally pass in front of it.
Quick Facts
- Apparent visual magnitude
- about 3.0
- Distance from sun
- roughly 440 light-years
- Bayer designation
- ζ Tauri (Zeta Tauri)
- Flamsteed designation
- 123 Tauri
- Spectral type (primary)
- B2 IIIpe
- Orbital period
- nearly 133 days
- Separation of components
- about 1.17 astronomical units
Facts from the source article.
Nomenclature
The Bayer designation for this star is ζ Tauri, Latinised to Zeta Tauri, and it also carries the Flamsteed designation 123 Tauri. The two components are designated Zeta Tauri A and B according to the convention of the Washington Multiplicity Catalog, adopted by the International Astronomical Union. In Chinese astronomy, Zeta Tauri is called 天關 (Tiānguān), meaning Celestial [Frontier] Gate, an asterism within the Net mansion. The IAU Working Group on Star Names approved the name Tianguan for the component Zeta Tauri A in 2017.
Properties
Zeta Tauri is a single-lined spectroscopic binary, meaning the two components orbit too close to be resolved telescopically; the primary's orbital motion is detected through Doppler shifts in its spectrum. The components are separated by an estimated 1.17 astronomical units and follow circular orbits with a period of nearly 133 days. The primary, Zeta Tauri A, is a giant star with more than 11 times the Sun's mass and 5–6 times its radius, rotating rapidly. Its stellar classification is B2 IIIpe, where 'III' indicates a giant that has exhausted core hydrogen, 'p' denotes a chemical peculiarity, and 'e' signifies emission lines from a rotating circumstellar disk of ejected gas. An oscillatory pattern in the spectrum is caused by a single-armed spiral density wave in the disk, which may precess due to the secondary's gravity. The companion, Zeta Tauri B, has about 94% of the Sun's mass and has been proposed to be a white dwarf accreting mass from the Be star, which would explain its hard X-ray emission. Zeta Tauri shows variation in spectrum and brightness; it is listed as an eclipsing variable and a Gamma Cassiopeiae variable in the General Catalogue of Variable Stars, but studies have failed to confirm the presence of eclipses.
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