Article · Wikipedia archive · Last revised Jul 7, 2026

Mu2 Octantis

Mu2 Octantis (μ2 Oct) is a binary star system in the constellation Octans, whose primary and secondary stars have apparent magnitudes of +6.481 and 7.153, respectively. Based on parallax measurements, it lies 130.3 light-years away.

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Mu2 Octantis
Location of μ2 Octantis (circled in red)
Observation data
Epoch J2000.0      Equinox ICRS
Constellation Octans
μ2 Oct A
Right ascension 20h 41m 44.1016s1
Declination −75° 21′ 02.883″1
Apparent magnitude (V) +6.481±0.0072
μ2 Oct B
Right ascension 20h 41m 45.5181s3
Declination −75° 20′ 47.047″3
Apparent magnitude (V) +7.153±0.0112
Characteristics
μ2 Oct A
Spectral type G1V4
U−B color index +0.265
B−V color index +0.625
μ2 Oct B
Spectral type G1V6
Astrometry
μ2 Oct A
Radial velocity (Rv)−11.00±0.121 km/s
Proper motion (μ) RA: 156.404 mas/yr1
Dec.: −162.214 mas/yr1
Parallax (π)25.0327±0.0205 mas1
Distance130.3 ± 0.1 ly
(39.95 ± 0.03 pc)
Absolute magnitude (MV)3.284
μ2 Oct B
Radial velocity (Rv)−10.94±0.153 km/s
Proper motion (μ) RA: +163.531 mas/yr3
Dec.: −171.346 mas/yr3
Parallax (π)25.0379±0.0167 mas3
Distance130.27 ± 0.09 ly
(39.94 ± 0.03 pc)
Orbit4
Semi-major axis (a)932 AU
Details7
μ2 Oct A
Mass1.330±0.013 M☉
Radius1.730+0.044
−0.039 R☉
Luminosity3.54+0.27
−0.208 L☉
Surface gravity (log g)4.09±0.028 cgs
Temperature6,059±52 K
Metallicity [Fe/H]+0.216±0.009 dex
Rotation22.5±2.98 days
Rotational velocity (v sin i)1.454 km/s
Age3.50+0.65
−0.27 Gyr
μ2 Oct B
Mass1.190+0.017
−0.018 M☉
Radius1.190+0.034
−0.010 R☉
Temperature6,020±52 K
Metallicity [Fe/H]+0.267±0.009 dex
Age2.10+1.03
−0.34 Gyr
Other designations
μ2 Oct, CCDM J20417-7521
μ2 Oct A: CD−75°1173, HD 196067, HIP 102125, HR 7864, SAO 257836, 2MASS J20414409-7521029
μ2 Oct B: CD−75°1174, HD 196068, HIP 102128, SAO 257837, 2MASS J20414550-7520471
Database references
SIMBADA
B
Exoplanet Archivedata

Mu2 Octantis (μ2 Oct) is a binary star system in the constellation Octans, whose primary and secondary stars have apparent magnitudes of +6.481 and 7.153, respectively.2 Based on parallax measurements, it lies 130.3 light-years away.13

The two stars, HD 196067 and HD 196068 (also named μ2 Oct A and μ2 Oct B), are separated at 17 arcseconds in the sky, corresponding to 740 astronomical units (AU). The semimajor axis of the stars' orbit is 932 AU.4

Component A is a G-dwarf star with 1.33 and 1.73 times of the Sun's mass and radius, respectively. Component B also a G-type main-sequence star with a radius 1.19 times larger than the Sun. Their effective temperatures are similar. HD 196068 has a higher metallicity than its companion, the reasons for this are uncertain.7

Planetary system

From 1998 to 2012, the system was observed using the CORALIE instrument, at the ESO's La Silla Observatory.4

In November 2012, a long-period, wide-orbiting planet was deduced by radial velocity around HD 196067. The planet has been pulled to an eccentric orbit by the B star HD 196068. The planet's true mass, as measured by astrometry, is 12.5 MJ, placing it right on the traditionally adopted boundary between planets and brown dwarfs.9

A second, innermost planet was detected using radial velocity observations with the CORALIE, HARPS, and ESPRESSO observatories. Despite its small orbit, it does not transit the host star.8

The μ2 Oct A planetary system8
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination
(°) 		Radius
c ≥10.4±1.39 M🜨 — 4.601088±0.000192 0.235±0.118 — —
b 11.4±1.6 MJ 4.71+0.11
−0.10 		3,413.7±10.5 0.56292±0.00703 29.7+5.0
−3.8 		—
References

References

  1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. Paunzen, E. (2015-08-01). "A new catalogue of Strömgren-Crawford uvbyβ photometry". Astronomy and Astrophysics. 580: A23. arXiv:1506.04568. Bibcode:2015A&A...580A..23P. doi:10.1051/0004-6361/201526413. ISSN 0004-6361.
  3. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  4. Marmier, M.; et al. (2013). "The CORALIE survey for southern extrasolar planets XVII. New and updated long period and massive planets". Astronomy and Astrophysics. 551. A90. arXiv:1211.6444. Bibcode:2013A&A...551A..90M. doi:10.1051/0004-6361/201219639. S2CID 59467665.
  5. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  6. Gray, R. O.; et al. (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.
  7. Flores, M; Yana Galarza, J; Miquelarena, P; Saffe, C; Jaque Arancibia, M; Ibañez Bustos, R V; Jofré, E; Alacoria, J; Gunella, F (2023-12-06). "Elemental abundance differences in the massive planet-hosting wide binary HD 196067−68". Monthly Notices of the Royal Astronomical Society. 527 (4): 10016–10024. arXiv:2311.17272. doi:10.1093/mnras/stad3714. ISSN 0035-8711.
  8. Delisle, J.-B.; Faria, J. P.; Ségransan, D.; Fontanet, E.; Ceva, W.; Barbato, D.; Sousa, S. G.; Unger, N.; Leleu, A. (2025-09-30). "Architecture of planetary systems with and without outer giant planets I. Inner planet detections around HD 23079, HD 196067, and HD 86226". Astronomy & Astrophysics. arXiv:2509.26232.
  9. Li, Yiting; Brandt, Timothy D.; Brandt, G. Mirek; Dupuy, Trent J.; Michalik, Daniel; Jensen-Clem, Rebecca; Zeng, Yunlin; Faherty, Jacqueline; Mitra, Elena L. (2021). "Precise Masses and Orbits for Nine Radial-velocity Exoplanets". The Astronomical Journal. 162 (6): 266. arXiv:2109.10422. Bibcode:2021AJ....162..266L. doi:10.3847/1538-3881/ac27ab. S2CID 237592581.