| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cetus |
| Right ascension | 02h 37m 41.80208s[1] |
| Declination | −03° 23′ 46.2259″[1] |
| Apparent magnitude (V) | 5.65[2] |
| Characteristics | |
| Evolutionary stage | red clump[3] |
| Spectral type | K0III[4] or G5III[5] |
| B−Vcolor index | 1.021±0.001[2] |
| Astrometry | |
| Radial velocity (Rv) | +9.14±0.12[1] km/s |
| Proper motion (μ) | RA: 41.765mas/yr[1] Dec.: −43.379mas/yr[1] |
| Parallax (π) | 9.5199±0.0756 mas[1] |
| Distance | 343 ± 3 ly (105.0 ± 0.8 pc) |
| Absolute magnitude (MV) | 0.82[2] |
| Details[6] | |
| Mass | 1.6±0.2 M☉ |
| Radius | 11.1±0.3 R☉ |
| Luminosity | 60.0±0.8 L☉ |
| Surface gravity (log g) | 2.5±0.1 cgs |
| Temperature | 4,825±41 K |
| Metallicity[Fe/H] | 0.00±0.04[7] dex |
| Rotational velocity (v sin i) | 1.20±0.47[7] km/s |
| Age | 2.5±0.9 Gyr |
| Other designations | |
| 81 Cet,BD−04°436,GC 3158,HD 16400,HIP 12247,HR 771,SAO 130026 | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
81 Ceti is astar located approximately 343 light-years away from the Sun in theequatorialconstellation ofCetus.81 Ceti is theFlamsteed designation for this object. It is visible to the naked eye as a dim, yellow-hued point of light with anapparent visual magnitude of 5.65.[2] The star is drifting further away from the Earth with a heliocentricradial velocity of +9 km/s.[2]
This is an agingK-typegiant star with astellar classification of K0III,[4] having exhausted the supply of hydrogen at itscore and expanded to 11[6] times theSun's radius. It is ared clump giant,[3] which indicates it is on thehorizontal branch and is generating energy from corehelium fusion. The star is now 2.5 billion years old with 1.6 times themass of the Sun.[6] It is radiating 60 times theluminosity of the Sun from its enlargedphotosphere at aneffective temperature of 4,825 K.[6]
In July 2008, the planet81 Ceti b was announced by Sato and collaborators, along with14 Andromedae b and6 Lyncis b. The planet was found to be asuper-Jupiter, with 5.3 timesthe mass of Jupiter. It takes 953 days for it to complete its orbit around the star.[5] The planetary parameters were updated in 2023.[8]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥3.307+0.078 −0.067 MJ | 2.104±0.003 | 1005.57+1.84 −1.94 | 0.037+0.015 −0.025 | — | — |
