Nu Octantis

ν Octantis
Location of ν Octantis in Octans (circled)
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−B color index +0.89[4]
B−V color index +1.00[4]
B
Evolutionary stage Either a main sequence star or a white dwarf[5]
Spectral type K7–M0V or WD[5]
Astrometry
Radial velocity (Rv)+34.40[6] km/s
Proper motion (μ) RA: +66.41 mas/yr[1]
Dec.: −239.10 mas/yr[1]
Parallax (π)45.25 ± 0.25 mas[7]
Distance72.1 ± 0.4 ly
(22.1 ± 0.1 pc)
Absolute magnitude (MV)2.3±0.16[5]
Orbit[8]
Period (P)1050.69+0.05
−0.07 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
Mass1.61[8] M☉
Radius5.81±0.12[8] R☉
Luminosity17.53[2] L☉
Surface gravity (log g)3.12±0.10[8] cgs
Temperature4,860±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]
Mass0.585[8] 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
SIMBADdata

ν Octantis, Latinised as Nu Octantis, is a star in the constellation of Octans. Unusually, 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.[7]

The primary has a spectral type of K1III,[3] with the luminosity class III indicating that it is a giant star that has burned up the hydrogen at its core and has expanded. Nu Octantis A has 1.6 times the mass of the Sun, but has expanded to 5.8 times the radius of the Sun.[8] Its photosphere has cooler to an effective temperature of 4,860 K[7] and now is radiating 18 times as much luminosity as the Sun.[2] It possibly hosts an extrasolar planet, a jovian planet on a retograde orbit.[5]

The secondary star is likely either a red dwarf or a white dwarf, from its relatively low mass.[5] This star is estimated to have around 60% the mass of the Sun. It shares a center of mass with the primary, completing an orbit around it every 2 years and 11 months. The orbit has an eccentricity of 0.24 and a semi-major axis of 2.63 au.[8]

Planetary system

In 2009, the system was hypothesised to contain a superjovian exoplanet based on perturbations in the orbital period.[7] A prograde solution was quickly ruled out[10] but a retrograde 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]

The Nu Octantis A planetary system[8]
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° —

See also

References

  1. ^ 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
  2. ^ a b c d 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
  3. ^ a b 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. S2CID 119476992.
  4. ^ 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
  5. ^ a b c d e f g 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.
  6. ^ 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.
  7. ^ a b c d e 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.
  8. ^ a b c d e f g h i j k 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.
  9. ^ 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.
  10. ^ 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.
  11. ^ 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.
  12. ^ 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.

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