Mu2 Octantis

Mu² Octantis
Observation data; Epoch J2000.0 Equinox J2000.0
Constellation	Octans
	μ2 Oct A
Right ascension	20h 41m 44.102s
Declination	−75° 21′ 02.88″
Apparent magnitude (V)	+6.481±0.007
	μ2 Oct B
Right ascension	20h 41m 45.5181s
Declination	−75° 20′ 47.047″
Apparent magnitude (V)	+7.153±0.011
Characteristics
μ2 Oct A
Spectral type	G1V
U−B color index	+0.26
B−V color index	+0.62
μ2 Oct B
Spectral type	G1V
Astrometry
μ2 Oct A
Radial velocity (Rv)	−10.90±0.2 km/s
Proper motion (μ)	RA: 156.404 mas/yr ; Dec.: −162.214 mas/yr
Parallax (π)	25.0327±0.0205 mas
Distance	130.3 ± 0.1 ly ; (39.95 ± 0.03 pc)
Absolute magnitude (MV)	3.28
μ2 Oct B
Radial velocity (Rv)	−10.94±0.15 km/s
Proper motion (μ)	RA: +163.531 mas/yr ; Dec.: −171.346 mas/yr
Parallax (π)	25.0379±0.0167 mas
Distance	130.27 ± 0.09 ly ; (39.94 ± 0.03 pc)
Orbit
Semi-major axis (a)	932 AU
Details
μ2 Oct A
Mass	1.330±0.013 M☉
Radius	1.730+0.044; −0.039 R☉
Luminosity	3.73 L☉
Surface gravity (log g)	4.24±0.03 cgs
Temperature	6,059±52 K
Metallicity [Fe/H]	+0.216±0.009 dex
Rotation	22.5±2.9 days
Rotational velocity (v sin i)	1.45 km/s
Age	3.50+0.65; −0.27 Gyr
μ2 Oct B
Mass	1.190+0.017; −0.018 M☉
Radius	1.190+0.034; −0.010 R☉
Temperature	6,020±52 K
Metallicity [Fe/H]	+0.267±0.009 dex
Age	2.10+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
A
SIMBAD	data
Exoplanet Archive	data
Database references
B
SIMBAD	data

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.^[1]^[3]

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.^[8]

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 M_J, placing it right on the traditionally adopted boundary between planets and brown dwarfs.^[10]

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.^[9]

The μ² Oct A planetary system^[9]
Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
c	≥10.4±1.4 $M$ _🜨	—	4.601088±0.000192	0.24±0.12	—	—
b	12.5+2.5 −1.8^[10] $M$ _J	5.10+0.22 −0.17^[10]	3,413.7±10.5	0.56292±0.00703	41.2+28 −9.1^[10]°	—

References

^ ^a ^b ^c ^d ^e 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.
^ ^a ^b ^c 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.
^ ^a ^b ^c ^d ^e ^f 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.
^ ^a ^b ^c ^d ^e ^f ^g ^h 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.
^ ^a ^b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
^ 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.
^ Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
^ ^a ^b 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.
^ ^a ^b ^c 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". arXiv:2509.26232 [astro-ph.EP].
^ ^a ^b ^c ^d 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.

[dr3a-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.

[Paunzen2015-2] 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.

[dr3b-3] ^ ^a ^b ^c ^d ^e ^f 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.

[Marmier2013-4] ^ ^a ^b ^c ^d ^e ^f ^g ^h 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.

[Mermilliod1986-5] Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.

[Gray2006-6] 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.

[Gontcharov2006-7] Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.

[Flores2023-8] 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.

[Delisle2025-9] 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". arXiv:2509.26232 [astro-ph.EP].

[Li2021-10] 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.

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Observation data Epoch J2000.0 Equinox J2000.0
Constellation	Octans
μ² Oct A
Right ascension	20^h 41^m 44.102^s^[1]
Declination	−75° 21′ 02.88″^[1]
Apparent magnitude (V)	+6.481±0.007^[2]
μ² Oct B
Right ascension	20^h 41^m 45.5181^s^[3]
Declination	−75° 20′ 47.047″^[3]
Apparent magnitude (V)	+7.153±0.011^[2]
Characteristics
μ² Oct A
Spectral type	G1V^[4]
U−B color index	+0.26^[5]
B−V color index	+0.62^[5]
μ² Oct B
Spectral type	G1V^[6]
Astrometry
μ² Oct A
Radial velocity (R_v)	−10.90±0.2^[7] km/s
Proper motion (μ)	RA: 156.404 mas/yr^[1] Dec.: −162.214 mas/yr^[1]
Parallax (π)	25.0327±0.0205 mas^[1]
Distance	130.3 ± 0.1 ly (39.95 ± 0.03 pc)
Absolute magnitude (M_V)	3.28^[4]
μ² Oct B
Radial velocity (R_v)	−10.94±0.15^[3] km/s
Proper motion (μ)	RA: +163.531 mas/yr^[3] Dec.: −171.346 mas/yr^[3]
Parallax (π)	25.0379±0.0167 mas^[3]
Distance	130.27 ± 0.09 ly (39.94 ± 0.03 pc)
Orbit^[4]
Semi-major axis (a)	932 AU
Details^[8]
μ² Oct A
Mass	1.330±0.013 `M`_☉
Radius	1.730+0.044 −0.039 `R`_☉
Luminosity	3.73^[4] `L`_☉
Surface gravity (log g)	4.24±0.03^[4] cgs
Temperature	6,059±52 K
Metallicity [Fe/H]	+0.216±0.009 dex
Rotation	22.5±2.9^[9] days
Rotational velocity (v sin i)	1.45^[4] km/s
Age	3.50+0.65 −0.27 Gyr
μ² Oct B
Mass	1.190+0.017 −0.018 `M`_☉
Radius	1.190+0.034 −0.010 `R`_☉
Temperature	6,020±52 K
Metallicity [Fe/H]	+0.267±0.009 dex
Age	2.10+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
A
SIMBAD	data
Exoplanet Archive	data
Database references
B
SIMBAD	data

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