Tau Tauri
Star system in the constellation Taurus
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Tau Tauri, Latinized from τ Tauri (τ Tau) formally named Gaja,[14] is a quadruple star system[5] in the constellation Taurus. It is visible to the naked eye as a faint point of light with a combined apparent visual magnitude of 4.33.[15] The distance to this system is approximately about 400 light years based on parallax.[1] The system is moving further from the Earth with a heliocentric radial velocity of +14.6 km/s,[7] and it is a member of the Taurion OB association, located between Orion and Taurus.[16] It is located 0.7 degree north of the ecliptic, and thus is subject to lunar occultations.[4]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Taurus |
| Right ascension | 04h 42m 14.70161s[1] |
| Declination | +22° 57′ 24.9214″[1] |
| Apparent magnitude (V) | 4.27[2] |
| Characteristics | |
| Spectral type | B3V[3] + ? + A0V–A2V[4] + A1V[5] |
| U−B color index | -0.57[6] |
| B−V color index | -0.14[6] |
| Astrometry | |
| Radial velocity (Rv) | +14.60[7] km/s |
| Proper motion (μ) | RA: -2.89[1] mas/yr Dec.: -21.86[1] mas/yr |
| Parallax (π) | 8.19±0.88 mas[1] |
| Distance | approx. 400 ly (approx. 120 pc) |
| Absolute magnitude (MV) | -1.15[2] |
| Orbit[8] | |
| Primary | Aa |
| Period (P) | 2.956549±0.000002 d |
| Semi-major axis (a) | ≤ 0.01455 AU |
| Eccentricity (e) | 0.051±0.019 |
| Periastron epoch (T) | 2,436,424.207±0.009 JD |
| Argument of periastron (ω) (secondary) | 126.7±21.8° |
| Semi-amplitude (K1) (primary) | 53.6±1.0 km/s |
| Details | |
| Aa | |
| Mass | 6.4[9] M☉ |
| Luminosity | 1,472[10] L☉ |
| Surface gravity (log g) | 2.60[11] cgs |
| Temperature | 18,700[10] K |
| Metallicity [Fe/H] | -0.51[11] dex |
| Rotational velocity (v sin i) | 115[12] km/s |
| Other designations | |
| Gaja, τ Tau, 94 Tauri, BD+22°739, FK5 174, GC 5716, HD 29763, HIP 21881, HR 1497, SAO 76721, CCDM J04422+2257AB, WDS J04422+2257A, GSC 01830-02129[13] | |
| Database references | |
| SIMBAD | data |
The blue-white hued primary, component Aa, is a B-type main-sequence star with a stellar classification of B3V.[3] It was found to be a close spectroscopic binary in 1903 by American astronomers Edwin B. Frost and Walter S. Adams. The pair have an orbital period of 2.96 days and eccentricity of 0.05.[8] A second companion, white-hued component Ab, has magnitude 6.97 and angular separation 0.2" from the primary in a 58-year orbit.[17][5] This is a probably A-type main-sequence star with a class of A0V–A2V.[4] The more distant component B is a type A1V star with magnitude 7.2 and separation 62.8".[5]
Nomenclature
Tau Tauri, Latinized from τ Tauri, is the star's Bayer designation. The term gaja(h) (Sanskrit: गज) means elephant, and is the name of a constellation from Bali (Indonesia) corresponding to Taurus, attested in the cultural calendar called Palelintangan.[18] The IAU Working Group on Star Names approved the name Gaja for Tau Tauri Aa (in the elephant's tusk) on 22 February 2026.[14]