Mu Orionis

μ Orionis
	Location of μ Ori (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Orion
	μ Ori A
Right ascension	06h 02m 22.997s
Declination	+09° 38′ 50.24″
Apparent magnitude (V)	4.30
	μ Ori B
Right ascension	06h 02m 23.009s
Declination	+09° 38′ 50.52″
Apparent magnitude (V)	6.27
Characteristics
μ Ori A
Spectral type	A1 Vm
U−B color index	+0.11
B−V color index	+0.14
μ Ori B
Spectral type	F2 V
U−B color index	+0.00
B−V color index	+0.43
Astrometry
Radial velocity (Rv)	0.00 km/s
Proper motion (μ)	RA: 10.43 mas/yr ; Dec.: −39.09 mas/yr
Parallax (π)	21.69 ± 0.13 mas
Distance	150.4 ± 0.9 ly ; (46.1 ± 0.3 pc)
Absolute magnitude (MV)	Aa: 0.93; Ba: 3.53; Bb: 3.53
Orbit
Primary	μ Ori A
Companion	μ Ori B
Period (P)	6,813.8±1.2 d
Semi-major axis (a)	0.2737±0.0021"; (12.620±0.057 AU)
Eccentricity (e)	0.7410±0.0011
Inclination (i)	96.028±0.028°
Orbit
Primary	μ Ori Aa
Companion	μ Ori Ab
Period (P)	4.4475849 days
Semi-major axis (a)	0.001661±0.000013"; (0.07659±0.00058 AU)
Eccentricity (e)	0.0037±0.0014
Inclination (i)	47.1±9.0°
Semi-amplitude (K1); (primary)	1.03±0.26 km/s
Semi-amplitude (K2); (secondary)	> 4.58 km/s
Orbit
Primary	μ Ori Ba
Companion	μ Ori Bb
Period (P)	4.7835349 days
Semi-major axis (a)	0.001688±0.000013"; (0.07659±0.00036 AU)
Eccentricity (e)	0.0016±0.0014
Inclination (i)	110.71±0.73°
Semi-amplitude (K1); (primary)	1.72±0.26 km/s
Semi-amplitude (K2); (secondary)	2.02±0.26 km/s
Details
μ Ori Aa
Mass	2.38 M☉
Radius	2.85 R☉
Luminosity	32.2 L☉
Temperature	8,300 K
Rotational velocity (v sin i)	10 km/s
Age	282 Myr
μ Ori Ab
Mass	0.652 M☉
μ Ori Ba
Mass	1.389 M☉
Radius	1.33 R☉
Luminosity	3.0 L☉
Temperature	6,600 K
μ Ori Bb
Mass	1.356 M☉
Radius	1.33 R☉
Luminosity	3.0 L☉
Temperature	6,600 K
Other designations
	Mu Orionis, Mu Ori, μ Orionis, μ Ori, 61 Orionis, 61 Ori, HR 2124, HD 40932, HIP 28614, BD+09°1064, ADS 4617, WDS J06024+0939, 2MASS J05351889-0516140
Database references
SIMBAD	data
	data2
	data3

μ Orionis (Latinised to Mu Orionis, abbreviated to μ Ori or Mu Ori) is a quadruple star system^[6] in the constellation Orion, similar to Mizar and Epsilon Lyrae with combined visual magnitude of 4.13. The four stars are known as Mu Orionis Aa, Mu Orionis Ab, Mu Orionis Ba, and Mu Orionis Bb. The A and B systems are several tenths of an arcsecond apart. The entire system is located approximately 150 light years from the Sun.

Mu Orionis Aa is an A5V dwarf and metallic line star, of effective temperature 8,350 Kelvin, and apparent magnitude of +4.31. Mu Orionis Aa has 2.1 solar masses, and a radius of 2.9 R_☉ and a luminosity 32 times that of the Sun.

Mu Orionis Ab is a G5V dwarf orbiting Aa at a distance of 0.077 AU, 0.2x the orbit of Mercury.

Mu Orionis Ba and Bb are F5V dwarfs with 1.4 solar masses and apparent magnitudes of 6.91. They are separated from each other by 0.078 AU.

μ Orionis falls just outside an unrelated planetary nebula Abell 12. The bright star makes detecting the faint nebula difficult and it has been nicknamed The Hidden.^{[citation needed]}

References

^ ^a ^b ^c ^d Fabricius, C.; Høg, E.; Makarov, V. V.; Mason, B. D.; Wycoff, G. L.; Urban, S. E. (2002). "The Tycho double star catalogue". Astronomy and Astrophysics. 384: 180–189. Bibcode:2002A&A...384..180F. doi:10.1051/0004-6361:20011822.
^ ^a ^b Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
^ ^a ^b ^c ^d ^e ^f Fekel, Francis C.; Scarfe, C. D.; Barlow, D. J.; Hartkopf, William I.; Mason, Brian D.; McAlister, Harold A. (2002). "The Quadruple System μ Orionis: Three-dimensional Orbit and Physical Parameters". The Astronomical Journal. 123 (3): 1723. Bibcode:2002AJ....123.1723F. doi:10.1086/339184.
^ Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; Levato, H.; Morrell, N. I.; Torres, G.; Udry, S. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. S2CID 119387088.
^ ^a ^b 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.
^ ^a ^b ^c ^d ^e ^f Muterspaugh, Matthew W.; et al. (2008). "Masses, Luminosities, and Orbital Coplanarities of the μ Orionis Quadruple-Star System from Phases Differential Astrometry". The Astronomical Journal. 135 (3): 766–776. arXiv:0710.2126. Bibcode:2008AJ....135..766M. doi:10.1088/0004-6256/135/3/766. S2CID 6531922.
^ Fekel, Francis C. (2003). "Rotational Velocities of B, A, and Early-F Narrow-lined Stars". The Publications of the Astronomical Society of the Pacific. 115 (809): 807–810. Bibcode:2003PASP..115..807F. doi:10.1086/376393.
^ Piccotti, Luca; Docobo, José Ángel; Carini, Roberta; Tamazian, Vakhtang S.; Brocato, Enzo; Andrade, Manuel; Campo, Pedro P. (2020). "A study of the physical properties of SB2s with both the visual and spectroscopic orbits". Monthly Notices of the Royal Astronomical Society. 492 (2): 2709. Bibcode:2020MNRAS.492.2709P. doi:10.1093/mnras/stz3616.