Chi Tauri
Chi Tauri, Latinised from χ Tauri, is a star system in the constellation of Taurus. Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 291 light-years (89 parsecs) from Earth. The primary component has an apparent magnitude of about 5.4, meaning it is visible with the naked eye.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Taurus |
| χ Tau A | |
| Right ascension | 04h 22m 34.944s |
| Declination | +25° 37′ 45.53″ |
| Apparent magnitude (V) | 5.378 |
| χ Tau B | |
| Right ascension | 04h 22m 35.550s |
| Declination | +25° 38′ 03.22″ |
| Apparent magnitude (V) | 8.423 |
| Characteristics | |
| χ Tau A | |
| Spectral type | B9V |
| U−B color index | -0.12 |
| B−V color index | -0.04 |
| χ Tau B | |
| Spectral type | F8 + G6 + K4 + K4 |
| U−B color index | +0.10 |
| B−V color index | +0.63 |
| Astrometry | |
| χ Tau A | |
| Radial velocity (Rv) | +15.3 ± 3.4 km/s |
| Proper motion (μ) | RA: 20.953 mas/yr Dec.: -16.495 mas/yr |
| Parallax (π) | 11.0472 ± 0.1599 mas |
| Distance | 295 ± 4 ly (91 ± 1 pc) |
| Absolute magnitude (MV) | 0.82 ± 0.18 |
| χ Tau B | |
| Radial velocity (Rv) | +14.694 ± 0.081 km/s |
| Proper motion (μ) | RA: 15.766 mas/yr Dec.: −20.396 mas/yr |
| Parallax (π) | 11.5348 ± 0.0857 mas |
| Distance | 283 ± 2 ly (86.7 ± 0.6 pc) |
| Absolute magnitude (MV) | 3.85 ± 0.18 (total) 4.20 ± 0.18 (Ba) 5.27 ± 0.18 (Bb) 7.87 / 7.87 (Bc) |
| Orbit | |
| Primary | χ Tau Ba |
| Companion | χ Tau Bb |
| Period (P) | 17.602309 ± 0.000036 d |
| Eccentricity (e) | 0.2938 ± 0.0013 |
| Inclination (i) | 53.3 ± 0.5° |
| Periastron epoch (T) | 2,448,891.649 ± 0.014 |
| Argument of periastron (ω) (secondary) | 249.43 ± 0.33° |
| Semi-amplitude (K1) (primary) | 41.287 ± 0.080 km/s |
| Semi-amplitude (K2) (secondary) | 48.133 ± 0.080 km/s |
| Orbit | |
| Primary | χ Tau Bab |
| Companion | χ Tau Bc |
| Period (P) | 3,450.6 ± 6.1 d |
| Eccentricity (e) | 0.3560 ± 0.0068 |
| Inclination (i) | 73 ± 6° |
| Periastron epoch (T) | 2,447,546.5 ± 9.7 |
| Argument of periastron (ω) (secondary) | 250.3 ± 1.5° |
| Semi-amplitude (K1) (primary) | 8.625 ± 0.067 km/s |
| Details | |
| Age | 200 ± 50 Myr |
| χ Tau A | |
| Mass | 2.60 ± 0.05 M☉ |
| Radius | 2.15 R☉ |
| Surface gravity (log g) | 4.15 ± 0.14 cgs |
| Temperature | 10,300 ± 300 K |
| Rotational velocity (v sin i) | 263 km/s |
| χ Tau Ba | |
| Mass | 1.19 M☉ |
| Surface gravity (log g) | 4.5 cgs |
| Temperature | 6,180 ± 150 K |
| Rotational velocity (v sin i) | 1 ± 3 km/s |
| χ Tau Bb | |
| Mass | 1.02 M☉ |
| Surface gravity (log g) | 4.5 cgs |
| Temperature | 5,620 ± 150 K |
| Rotational velocity (v sin i) | 1 ± 3 km/s |
| χ Tau Bc | |
| Mass | ~0.70 / 0.70 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | χ Tau A |
| χ Tau B | |
The main component of the system is Chi Tauri A. It is a B-type main-sequence star. Its mass is 2.6 times that of the Sun and its surface glows with an effective temperature of 10,300 K. It may be a binary star itself, as suggested from astrometric data from Hipparcos, although no orbit could be derived.
The secondary component of the system is Chi Tauri B, separated about 19″ from Chi Tauri A. It was thought to be a post-T Tauri star from its unusual spectrum, but later studies ruled this out. It is a double-lined spectroscopic binary—the two stars are not resolved but their spectra have periodic Doppler shifts indicating orbital motion. The two stars are an F-type star and a G-type star, respectively, and are designated Ba and Bb.
The radial velocity of Chi Tauri B has a slow drift indicating the presence of another star in the system. Designated Chi Tauri Bc, this massive object is too dim to be detected, but it appears in Chi Tauri B's spectrum as an infrared excess. Because of this infrared excess, this unseen component is thought to be a pair of K-type main-sequence stars both with masses 70% of the Sun's. The stars within the system appear to be dynamically interacting.