  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Octans |
| Right ascension | 21h 41m 28.64977s[1] |
| Declination | −77° 23′ 24.1563″[1] |
| Apparent magnitude (V) | 3.73[2] |
| Characteristics | |
| A | |
| Evolutionary stage | Giant star |
| Spectral type | K1III[3] |
| U−Bcolor index | +0.89[4] |
| B−Vcolor index | +1.00[4] |
| B | |
| Evolutionary stage | Either a main sequence star or awhite dwarf[5] |
| Spectral type | K7–M0V or WD[5] |
| Astrometry | |
| Radial velocity (Rv) | +34.40[6] km/s |
| Proper motion (μ) | RA: +66.41mas/yr[1] Dec.: −239.10mas/yr[1] |
| Parallax (π) | 45.25±0.25 mas[7] |
| Distance | 72.1 ± 0.4 ly (22.1 ± 0.1 pc) |
| Absolute magnitude (MV) | 2.3±0.16[5] |
| Orbit[8] | |
| Period (P) | 1050.69+0.05 −0.07d |
| Semi-major axis (a) | 2.62959+0.00009 −0.00011AU |
| Eccentricity (e) | 0.23680±0.00007 |
| Inclination (i) | 70.8±0.9° |
| Longitude of the node (Ω) | 87±1.2° |
| Argument of periastron (ω) (secondary) | 74.970±0.016° |
| Semi-amplitude (K1) (primary) | 7.032±0.003 km/s |
| Details | |
| Nu Octantis A | |
| Mass | 1.61[8] M☉ |
| Radius | 5.81±0.12[8] R☉ |
| Luminosity | 17.53[2] L☉ |
| Surface gravity (log g) | 3.12±0.10[8] cgs |
| Temperature | 4,860±40[7] K |
| Metallicity [Fe/H] | +0.18±0.04[8] dex |
| Rotational velocity (v sin i) | 2.0[8] km/s |
| Age | ~2.5-3[8] Gyr |
| Nu Octantis B[5] | |
| Mass | 0.585[8] M☉ |
| Other designations | |
| nu Oct,CD−77 1079,CCDM J21415-7723,FK5 810,GC 30289,GJ 835.1, GJ 9744,HIP 107089,HR 8254,HD 205478,SAO 257948,WDS J21415-7723 | |
| Database references | |
| SIMBAD | data |
ν Octantis,Latinised asNu Octantis, is a star in theconstellation ofOctans. Unusually for having such a late greek letter in its name, it is the brightest star in this faint constellation atapparent magnitude +3.7.[2] It is aspectroscopic binary[9]star with a period around 2.9 years.Parallax measurements place it at 22.1 parsecs (72 ly) from Earth.[7]
The primary has aspectral type of K1III,[3] with theluminosity class III indicating that it is agiant star that has burned up thehydrogen at its core and has expanded. Nu Octantis A has 1.6 times themass of the Sun, but has expanded to 5.8 times theradius of the Sun.[8] Itsphotosphere has cooler to aneffective temperature of 4,860 K[7] and now is radiating 18 times as much luminosity as the Sun.[2] It possibly hosts anextrasolar planet, ajovian planet on a retograde orbit.[5]
The secondary star is likely either ared dwarf or awhite dwarf, from its relatively low mass.[5] This star is estimated to have around 60% the mass of the Sun. It shares acenter of mass with the primary, completing an orbit around it every 2 years and 11 months. The orbit has aneccentricity of 0.24 and asemi-major axis of 2.63 au.[8]
In 2009, the system was hypothesised to contain asuperjovianexoplanet based on perturbations in the orbital period.[7] Aprograde solution was quickly ruled out[10] but aretrograde solution remains a possibility, although the variations may instead be due to the secondary star being itself a close binary,[11] since the formation of a planet in such a system would be difficult due to dynamic perturbations.[12] Further evidence ruling out a stellar variability and favouring the existence of the planet was gathered by 2021.[5]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 2.1059 MJ | 1.276 | 414.8 | 0.086 | 112.5° | — |
