36 Tauri (abbreviated to 36 Tau) is a binary star in the constellation of Taurus. Parallax measurements made by the Hipparcos spacecraft put it at a distance of over 1,000 light years (350 parsecs) from Earth.[1] The combined apparent magnitude of the system is about 5.5,[2] meaning it can barely be seen with the naked eye, according to the Bortle scale.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Taurus |
| Right ascension | 04h 04m 21.67333s[1] |
| Declination | +24° 06′ 21.5720″[1] |
| Apparent magnitude (V) | 5.512[2] |
| Characteristics | |
| Spectral type | K0II + B7V[3] |
| Astrometry | |
| Radial velocity (Rv) | 10.38 ± 0.06[4] km/s |
| Proper motion (μ) | RA: -0.54[1] mas/yr Dec.: -14.08[1] mas/yr |
| Parallax (π) | 2.88 ± 0.43 mas[1] |
| Distance | approx. 1,100 ly (approx. 350 pc) |
| Absolute magnitude (MV) | -1.79 (-1.40 / -0.50)[3] |
| Orbit[3] | |
| Period (P) | 7.9412 ± 0.0093 yr |
| Semi-major axis (a) | 0.0289 ± 0.0024″ |
| Eccentricity (e) | 0.683 ± 0.006 |
| Inclination (i) | 149.4 ± 6.9° |
| Longitude of the node (Ω) | 260 ± 15° |
| Periastron epoch (T) | B 1985.092 ± 0.013 |
| Argument of periastron (ω) (secondary) | 287.7 ± 1.6° |
| Semi-amplitude (K1) (primary) | 8.69 ± 0.12 km/s |
| Other designations | |
| 36 Tauri A: HD 25555 | |
| 36 Tauri B: HD 25556 | |
| Database references | |
| SIMBAD | data |
36 Tauri is a spectroscopic binary. The two stars are close enough that periodic Doppler shifts in their spectra can be made out. In this case, light from both stars can be detected (and they overlap in the spectrum), so it is a double-lined system. The primary star, designated HD 25555, is a K-type bright giant, and the secondary star, designated HD 25556, is a B-type main-sequence star.[3] However, the spectrum has also been interpreted as a G-type star and an A-type main-sequence star.[5] The two stars have been resolved using speckle interferometry and are thought to have similar masses.[3]