Nu Octantis
  | |
| 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 | Subgiant[3] |
| Spectral type | K1IV[3] |
| U−B color index | +0.89[4] |
| B−V color index | +1.00[4] |
| B | |
| Evolutionary stage | white dwarf[3] |
| Astrometry | |
| Radial velocity (Rv) | +34.40[5] km/s |
| Proper motion (μ) | RA: +66.41 mas/yr[1] Dec.: −239.10 mas/yr[1] |
| Parallax (π) | 45.25±0.25 mas[6] |
| Distance | 73.5±0.68 ly (22.54±0.21 pc)[3] |
| Absolute magnitude (MV) | 2.3±0.16[7] |
| Orbit[3] | |
| Period (P) | 1050.74+0.20 −0.10 days |
| Semi-major axis (a) | 2.61±0.03 AU |
| Eccentricity (e) | 0.2366±0.0003 |
| Inclination (i) | 71.8+0.7 −0.6° |
| Longitude of the node (Ω) | 86.5±0.3° |
| Argument of periastron (ω) (secondary) | 74.88+0.06 −0.14° |
| Semi-amplitude (K2) (secondary) | 7.0648+0.0050 −0.0009 km/s |
| Details[3] | |
| Nu Octantis A | |
| Mass | 1.57±0.06 M☉ |
| Radius | 5.04±0.10 R☉ |
| Luminosity | 13.2±0.3 L☉ |
| Surface gravity (log g) | 3.23+0.02 −0.03 cgs |
| Temperature | 4,910+21 −30 K |
| Metallicity [Fe/H] | +0.18±0.04[8] dex |
| Rotational velocity (v sin i) | 2.0[8] km/s |
| Age | 2.70±0.35 Gyr |
| Nu Octantis B | |
| Mass | 0.57±0.01 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 as Nu Octantis, is a star in the constellation of Octans. Unusually for having such a late greek letter in its name, it is the brightest star in this faint constellation at apparent magnitude +3.7.[2] It is a spectroscopic binary[9] star with a period around 2.9 years. Parallax measurements place it at 22.1 parsecs (72 ly) from Earth.[6]
Characteristics
[edit]This is a spectroscopic binary system, meaning the binarity was inferred from periodic Doppler shifts in the spectral lines, which correspond to the motion of the stars.[10] Both stars take 1,050 days (2.9 years) to complete an orbit around each other, being separated by a semi-major axis of 2.61 astronomical units at a somewhat elliptical orbit.[3]
The primary has a spectral type of K1IV, with the luminosity class IV indicating that it is a subgiant star that has burned up the hydrogen at its core and has expanded. Nu Octantis A has 1.57 times the mass of the Sun, but has expanded to 5.04 times the radius of the Sun.[8] Its photosphere has cooled to an effective temperature of 4,910 K and now is radiating 13.2 times as much luminosity as the Sun.[3]
The secondary star is a white dwarf with 0.57 times the mass of the Sun. When it was on the main sequence, it had a mass of 2.36+0.13
−0.15 M☉ and was closer to its primary, at 1.31±0.07 AU. When it evolved to a red giant, and then to a white dwarf, it lost most of its mass, thus increasing the orbital separation. The primary star accreted about 0.2 M☉ from the secondary during this period.[3]
Planetary system
[edit]In 2009, the system was hypothesised to contain a superjovian exoplanet based on perturbations in the orbital period.[6] A prograde solution was quickly ruled out[11] but a retrograde solution remains a possibility, although a study posited that it may instead be due to the secondary star being itself a close binary,[12] since the formation of a planet in such a system would be difficult due to gravitational perturbations.[13] Further evidence ruling out a stellar variability and favouring the existence of the planet was gathered by 2021.[7] With new radial velocity measurements, a study in 2025 confirmed the planet's existence.[3]
The binary components in the Nu Octantis system were initially separated by 1.3 AU, which overlap with the current orbital separation of the planet. Therefore, the planet did not form in its current orbit, but either migrated from a longer, circumbinary orbit, or originated from a protoplanetary disc that formed after the death of the white dwarf's progenitor.[3]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 2.19±0.11 MJ | 1.24±0.02 | 402.4+7.7 −6.0 |
0.195+0.050 −0.037 |
108.2° | — |
See also
[edit]- Gamma Cephei and Nu2 Canis Majoris, another similar-sized giant stars hosting a jovian planet
- Beta Hydri
References
[edit]- ^ a b c Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Vizier catalog entry
- ^ a b Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644. Vizier catalog entry
- ^ a b c d e f g h i j k l Cheng, Ho Wan; Trifonov, Trifon; Lee, Man Hoi; Cantalloube, Faustine; Reffert, Sabine; Ramm, David; Quirrenbach, Andreas (May 2025). "A retrograde planet in a tight binary star system with a white dwarf". Nature. 641 (8064): 866–870. doi:10.1038/s41586-025-09006-x. ISSN 1476-4687. PMID 40399630.
- ^ a b Mallama, A. (2014). "Sloan Magnitudes for the Brightest Stars". The Journal of the American Association of Variable Star Observers. 42 (2): 443. Bibcode:2014JAVSO..42..443M.Vizier catalog entry
- ^ Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities". Carnegie Institute Washington D.C. Publication. Carnegie Institution for Science. Bibcode:1953GCRV..C......0W. LCCN 54001336.
- ^ a b c Ramm, D. J.; Pourbaix, D.; Hearnshaw, J. B.; Komonjinda, S. (April 2009). "Spectroscopic orbits for K giants β Reticuli and ν Octantis: what is causing a low-amplitude radial velocity resonant perturbation in ν Oct?". Monthly Notices of the Royal Astronomical Society. 394 (3): 1695–1710. Bibcode:2009MNRAS.394.1695R. doi:10.1111/j.1365-2966.2009.14459.x.
- ^ a b Ramm, D J; Robertson, P; et al. (2021). "A photospheric and chromospheric activity analysis of the quiescent retrograde-planet host ν Octantis A". Monthly Notices of the Royal Astronomical Society. 502 (2): 2793–2806. arXiv:2101.06844. doi:10.1093/mnras/stab078.
- ^ a b c Ramm, D. J.; et al. (2016). "The conjectured S-type retrograde planet in ν Octantis: more evidence including four years of iodine-cell radial velocities". Monthly Notices of the Royal Astronomical Society. 460 (4): 3706–3719. arXiv:1605.06720. Bibcode:2016MNRAS.460.3706R. doi:10.1093/mnras/stw1106.
- ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
- ^ Struve, Otto; Huang, Su Shu (1958). Flügge, S. (ed.). Spectroscopic Binaries. Berlin, Heidelberg: Springer. pp. 243–273. doi:10.1007/978-3-642-45906-1_8. ISBN 978-3-642-45906-1. Retrieved 2025-05-26.
{{cite book}}: ISBN / Date incompatibility (help);|work=ignored (help) - ^ Eberle, J.; Cuntz, M. (October 2010). "On the reality of the suggested planet in the ν Octantis system". The Astrophysical Journal. 721 (2): L168 – L171. Bibcode:2010ApJ...721L.168E. doi:10.1088/2041-8205/721/2/L168.
- ^ Morais, M. H. M.; Correia, A. C. M. (February 2012). "Precession due to a close binary system: an alternative explanation for ν-Octantis?". Monthly Notices of the Royal Astronomical Society. 419 (4): 3447–3456. arXiv:1110.3176. Bibcode:2012MNRAS.419.3447M. doi:10.1111/j.1365-2966.2011.19986.x. S2CID 119152109.
- ^ Gozdziewski, K.; Slonina, M.; Migaszewski, C.; Rozenkiewicz, A. (March 2013). "Testing a hypothesis of the ν Octantis planetary system". Monthly Notices of the Royal Astronomical Society. 430 (1): 533–545. arXiv:1205.1341. Bibcode:2013MNRAS.430..533G. doi:10.1093/mnras/sts652.
