Tau Orionis
Star in the constellation Orion
From Wikipedia, the free encyclopedia
Tau Orionis (τ Ori, τ Orionis) is a binary star in the constellation Orion. If an imaginary line is drawn north-west between the stars Rigel and Mintaka, Tau Orionis can be found roughly one-sixth of the way to Mintaka. It is visible to the naked eye with a combined apparent visual magnitude of 3.58.[2] Based upon an annual parallax shift of 6.6 mas,[1] it is located around 490 light years distant.
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Orion |
| Right ascension | 05h 17m 36.38856s[1] |
| Declination | −06° 50′ 39.8702″[1] |
| Apparent magnitude (V) | 3.58[2] |
| Characteristics | |
| Spectral type | B5 III[3] |
| U−B color index | −0.47[2] |
| B−V color index | −0.11[2] |
| Astrometry | |
| Radial velocity (Rv) | +20.1[4] km/s |
| Proper motion (μ) | RA: −17.61[1] mas/yr Dec.: −9.24[1] mas/yr |
| Parallax (π) | 6.60±0.15 mas[1] |
| Distance | 490 ± 10 ly (152 ± 3 pc) |
| Orbit[5] | |
| Period (P) | 90.29 days |
| Eccentricity (e) | 0.834 |
| Longitude of the node (Ω) | 156° |
| Details[5] | |
| A | |
| Mass | 6.6 M☉ |
| B | |
| Mass | 5.3 M☉ |
| Other designations | |
| τ Ori, 20 Orionis, BD−07°1028, HD 34503, HIP 24674, HR 1735, SAO 131952.[6] | |
| Database references | |
| SIMBAD | data |
This is a spectroscopic binary system with an orbital period of 90 days and a very high eccentricity of 0.834. It is a heartbeat star, showing variations on its apparent magnitude during the close periastron passage. The components have masses of 6.6 and 5.3 M☉[5] and a combined stellar classification of B5 III.[3] The star has a peculiar velocity through space of 16.9 km/s.[7]
Tau Orionis has three visual companions: magnitude 11.0 component B at an angular separation of 33.30″ along a position angle of 251°; magnitude 10.9 component C lying some 3.80″ from component B; and magnitude 10.9 component D at 36.0″ from τ Ori along a position angle of 51°, all as of 2011.[8]
Proper names
According to Richard H. Allen, this star, along with β Eri, λ Eri and ψ Eri were Al Kursiyy al Jauzah, "the Chair (or "Footstool") of the Central One".[9] However, per the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Kursiyy al Jauzah were the title for just three stars: β Eri as Cursa, ψ Eri as Al Kursiyy al Jauzah I and λ Eri as Al Kursiyy al Jauzah II, excluding this star.[10]
In Chinese, 玉井 (Yù Jǐng), meaning Jade Well, refers to an asterism consisting of τ Orionis, β Eridani, λ Eridani and ψ Eridani.[11] Consequently, the Chinese name for τ Orionis itself is 玉井四 (Yù Jǐng sì, English: the Fourth Star of Jade Well.).[12] From this Chinese title, the name Yuh Tsing is derived.[9]