Nu Octantis

ν Octantis, Latinised as Nu Octantis, is a spectroscopic binary[11] star in the constellation Octans with a period around 2.9 years.[9] Its apparent magnitude is 3.73.[2] Located around 21.20 parsecs (69.1 ly) distant,[1] the primary is an orange giant of spectral type K1III,[3] a star that has used up its core hydrogen and has expanded. The secondary star is likely either a red dwarf or a white dwarf, from its relatively low mass.[10]

ν Octantis

Location of ν Octantis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Octans
Right ascension	21^h 41^m 28.64977^s[1]
Declination	−77° 23′ 24.1563″[1]
Apparent magnitude (V)	3.73[2]
Characteristics
Spectral type	K1III[3]
U−B color index	+0.89[4]
B−V color index	+1.00[4]
Astrometry
Radial velocity (Rv)	+34.40[5] km/s
Proper motion (μ)	RA: +66.41[1] mas/yr Dec.: −239.10[1] mas/yr
Parallax (π)	51.5172 ± 0.6525[6] mas
Distance	63.3 ± 0.8 ly (19.4 ± 0.2 pc)
Absolute magnitude (MV)	+2.10[2] +2.02[7]
Orbit[7]
Period (P)	1050.69+0.05 −0.07 d
Semi-major axis (a)	2.62959+0.00009 −0.00011 AU
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	1.04[8] 1.61[7] M☉
Radius	5.9[8] 5.81±0.12[7] R☉
Luminosity	17.53[2] L☉
Surface gravity (log g)	3.12±0.10[7] cgs
Temperature	4,860±40[9] K
Metallicity [Fe/H]	+0.18±0.04[7] dex
Rotational velocity (v sin i)	2.0[7] km/s
Age	~2.5-3[7] Gyr
Nu Octantis B[10]
Mass	0.585[7] M☉
Other designations
nu Oct, CD−77 1079, CCDM J21415-7723, FK5 810, GC 30289, GJ 9744, HIP 107089, HR 8254, HD 205478, SAO 257948, WDS J21415-7723
Database references
SIMBAD	data

Planetary system

In 2009, the system was hypothesised to contain a superjovian exoplanet based on perturbations in the orbital period.[9] A prograde solution was quickly ruled out[12] but a retrograde solution remains a possibility, although the variations may instead be due to the secondary star being itself a close binary,[13] since the formation of a planet in such a system would difficult due to dynamic perturbations.[14] Further evidence ruling out a stellar variability and favouring the existence of the planet was gathered by 2021.[10]

The Nu Octantis A planetary system[7]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b (unconfirmed)	2.1059 MJ	1.276	414.8	0.086	112.5°	—

References

1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Vizier catalog entry
2. 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. Vizier catalog entry
3. Gray, R. O.; et al. (July 2006). "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637.
4. Mallama, A. (2014). "Sloan Magnitudes for the Brightest Stars". The Journal of the American Association of Variable Star Observers. 42: 443. Bibcode:2014JAVSO..42..443M.Vizier catalog entry
5. Wilson, R. E. (1953). General Catalogue of Stellar Radial Velocities. Carnegie Institution for Science. Bibcode:1953GCRV..C......0W. LCCN 54001336.
6. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
7. 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.
8. Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: Masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555. arXiv:astro-ph/9911002. Bibcode:1999A&A...352..555A. Vizier catalog entry
9. 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.
10. 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. arXiv:2101.06844. doi:10.1093/mnras/stab078.
11. 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.
12. 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.
13. 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.
14. 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.