Sigma Ceti
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Cetus |
| σ Cet A | |
| Right ascension | 02h 32m 05.22884s |
| Declination | −15° 14′ 40.8278″ |
| Apparent magnitude (V) | 4.75 |
| σ Cet B | |
| Right ascension | 02h 31m 42.47292s |
| Declination | −15° 16′ 24.4275″ |
| Apparent magnitude (V) | 8.74 |
| Characteristics | |
| σ Cet A | |
| Spectral type | F5 V or F4 IV |
| U−B color index | −0.03 |
| B−V color index | +0.45 |
| σ Cet B | |
| Spectral type | K2.5V |
| Astrometry | |
| σ Cet A | |
| Radial velocity (Rv) | −28.85±0.12 km/s |
| Proper motion (μ) | RA: −80.21 mas/yr Dec.: −146.29 mas/yr |
| Parallax (π) | 37.46±0.25 mas |
| Distance | 87.1 ± 0.6 ly (26.7 ± 0.2 pc) |
| Absolute magnitude (MV) | +2.68 |
| σ Cet B | |
| Proper motion (μ) | RA: −73.371 mas/yr Dec.: −117.842 mas/yr |
| Parallax (π) | 37.1885 ± 0.0188 mas |
| Distance | 87.70 ± 0.04 ly (26.89 ± 0.01 pc) |
| Absolute magnitude (MV) | +6.48 |
| Orbit | |
| Primary | σ Cet Aa |
| Companion | σ Cet Ab |
| Period (P) | 20.68±0.67 years |
| Semi-major axis (a) | 0.3616″±0.0049″ (9.65 AU) |
| Eccentricity (e) | 0.854±0.009 |
| Inclination (i) | 120.3±1.3° |
| Longitude of the node (Ω) | 23.1±1.3° |
| Argument of periastron (ω) (primary) | 23.4±2.6° |
| Semi-amplitude (K1) (primary) | 7.56±0.25 km/s |
| Position (relative to σ Cet A) | |
| Component | σ Cet B |
| Angular distance | 345″ |
| Projected separation | 9,800 AU |
| Details | |
| σ Cet Aa | |
| Mass | 1.45 M☉ |
| Radius | 2.108 R☉ |
| Luminosity | 6.95 L☉ |
| Surface gravity (log g) | 4.07±0.07 cgs |
| Temperature | 6,527±59 K |
| Metallicity [Fe/H] | −0.12±0.04 dex |
| Rotational velocity (v sin i) | 20 km/s |
| Age | 2.135 Gyr |
| σ Cet Ab | |
| Mass | 0.70 M☉ |
| σ Cet B | |
| Mass | 0.77 M☉ |
| Radius | 0.698±0.048 R☉ |
| Luminosity | 0.262±0.008 L☉ |
| Temperature | 4,935±145 K |
| Other designations | |
| A: σ Cet, 76 Cet, BD−15°449, FK5 1071, HD 15798, HIP 11783, HR 740, SAO 148445 | |
| B: HIP 11759, HD 15767, BD−15°447, TIC 66574369, SAO 148443 | |
| Database references | |
| SIMBAD | σ Cet A |
| σ Cet B | |
Sigma Ceti (σ Ceti) is a triple star system in the equatorial constellation of Cetus. With an apparent visual magnitude of 4.78, it can be seen with the naked eye on a dark night. Based upon an annual parallax shift of 37.46 mas, it lies at an estimated distance of 87.1 light years from the Sun.