  | |
| Observation data EpochJ2000.0 EquinoxJ2000.0 | |
|---|---|
| Constellation | Cetus |
| Right ascension | 01h 08m 35.39133s[1] |
| Declination | −10° 10′ 56.1519″[1] |
| Apparent magnitude (V) | +3.446[2] |
| Characteristics | |
| Evolutionary stage | Red-giant branch[3] |
| Spectral type | K2−IIIb[4] |
| U−Bcolor index | +1.194[2] |
| B−Vcolor index | +1.161[2] |
| Astrometry | |
| Radial velocity (Rv) | +11.74±0.30[5] km/s |
| Proper motion (μ) | RA: +215.922mas/yr[1] Dec.: −139.029mas/yr[1] |
| Parallax (π) | 27.0603±0.1799 mas[1] |
| Distance | 120.5 ± 0.8 ly (37.0 ± 0.2 pc) |
| Absolute magnitude (MV) | +0.68[6] |
| Details | |
| Mass | 1.7±0.1[3] M☉ |
| Radius | 13.2±0.1[7] R☉ |
| Luminosity | 74.0±3.7[8] L☉ |
| Surface gravity (log g) | 2.5[5] cgs |
| Temperature | 4,543±24[9] K |
| Metallicity[Fe/H] | −0.03[5] dex |
| Rotational velocity (v sin i) | 4.8[5] km/s |
| Age | 1.80[9] Gyr |
| Other designations | |
| Deneb Algenubi, Algenudi,31 Ceti,BD−10 240,FK5 40,HD 6805,HIP 5364,HR 334,SAO 147632,2MASS J01083539-1010560[10] | |
| Database references | |
| SIMBAD | data |
Eta Ceti (η Cet, η Ceti) is astar in theequatorialconstellation ofCetus. It has the traditional nameDeneb Algenubi orAlgenudi. Theapparent visual magnitude of this star is +3.4,[2] making it thefourth-brightest star in this otherwise relatively faint constellation. The distance to this star can be measured directly using theparallax technique, yielding a value of 120.5light-years (36.9parsecs).[1]
This is agiant star that has been chosen a standard for thestellar classification of K2−IIIb. It has exhausted the hydrogen at its core andevolved away from themain sequence of stars like the Sun. (The classification is sometimes listed as K1.5 IIICN1Fe0.5, indicating a strongCN star[11] with higher-than-normal abundance ofcyanogen and iron relative to other stars of its class.)[12] It is probably on thered giant branch fusing hydrogen in a shell, although there is a possibility that it is ared clump star that is generating energy through thenuclear fusion of helium at its core.[3]
Eta Ceti has 1.7 times more mass than the Sun[3] and its surface has expanded to 13 times the Sun's radius.[7] It is radiating 74[8] times as much luminosity as the Sun from its photosphere at aneffective temperature of 4,356 K.[8] This heat gives the star the orange-hued glow of aK-type star.[13]
The nameDeneb Algenubi was from Arabic ذنب القيطس الجنوبي – al-dhanab al-qayṭas al-janūbī, meaningthe southern tail of the sea monster. In the catalogue of stars in theCalendarium ofAl Achsasi al Mouakket, this star was designated Aoul al Naamat (أول النعامات –awwil al naʽāmāt), which was translated intoLatin as Prima Struthionum, meaningthe first ostrich.[14] This star, along withθ Cet (Thanih al Naamat),τ Cet (Thalath Al Naamat),ζ Cet (Baten Kaitos) andυ Cet, were Al Naʽāmāt (النعامات), the Hen Ostriches.[15]
InChinese,天倉 (Tiān Cāng), meaningSquare Celestial Granary, refers to anasterism consisting of η Ceti,ι Ceti,θ Ceti,ζ Ceti,τ Ceti and57 Ceti.[16] Consequently, theChinese name for η Ceti itself is天倉二 (Tiān Cāng èr, English:the Second Star of Square Celestial Granary).[17]
In 2014, twoexoplanets around the star were discovered using theradial velocity method. Planets discovered by radial velocity have poorly known masses because if the orbit of the planets were inclined away from the line of sight, a much larger mass would have to compensate for the angle in order to generate the measured signal.[18]
Eta Ceti b has a minimum mass of2.55 MJ and anorbital period of 403.5 days (about 1.1 years), while Eta Ceti c has a minimum mass of3.32 MJ and an orbital period of 751.9 days (2.06 years). Assuming the orbits of the two arecoplanar, then the two planets must be locked in a 2:1orbital resonance, otherwise the system would become dynamically unstable. Although the inclinations from the line of sight are unknown, the value is constrained to be 70° or less: if any higher, the higher masses would render the system dynamically unstable, with no stable solutions.[3]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥2.55 ± 0.13 MJ | 1.27 | 403.5 ± 1.5 | 0.13 ± 0.05 | — | — |
| c | ≥3.32 ± 0.18 MJ | 1.93 | 751.9 ± 3.8 | 0.1 ± 0.06 | — | — |
{{citation}}:ISBN / Date incompatibility (help)