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.^[2] Based on parallax measurements, it lies 130.3 light-years away.^[1][3]

For other stars with this Bayer designation, see μ Octantis.

Mu² Octantis

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Octans
μ2 Oct A
Right ascension	20h 41m 44.102s[1]
Declination	−75° 21′ 02.88″[1]
Apparent magnitude (V)	+6.481±0.007[2]
μ2 Oct B
Right ascension	20h 41m 45.5181s[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 (Rv)	−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 (MV)	3.28[4]
μ2 Oct B
Radial velocity (Rv)	−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	26±3[4] 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☉
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

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 boundary between planets and brown dwarfs.^[9]

The μ² Oct A planetary system^[9]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (years)	Eccentricity	Inclination	Radius
b	12.5+2.5 −1.8 MJ	5.10+0.22 −0.17	9.88+0.63 −0.43	0.70+0.14 −0.12	41.2+28 −9.1°	—