Mu Canis Majoris

Mu Canis Majoris is a binary star^[2] system in the southern constellation of Canis Major. The pair can be located a little to the southwest of the point midway between Gamma and Theta Canis Majoris,^[13] and the components can be split with a small telescope.^[14] Their name is a Bayer designation that is Latinized from μ Canis Majoris, and abbreviated as Mu CMa or μ CMa. The system is faintly visible to the naked eye with a combined apparent visual magnitude of 5.12.^[2] Based upon an annual parallax shift of 3.42 mas as seen from Earth,^[1] this system is located roughly 950–960 light years from the Sun.

Mu Canis Majoris

Location of μ Canis Majoris (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Canis Major
μ CMa A
Right ascension	06h 56m 06.6459s[1]
Declination	−14° 02′ 36.351″[1]
Apparent magnitude (V)	5.27[2]
μ CMa B
Right ascension	06h 56m 06.5891s[3]
Declination	−14° 02′ 33.633″[3]
Apparent magnitude (V)	7.32[2]
Characteristics
Spectral type	K2/3 III + B9/A0 V[4]
Astrometry
μ CMa A
Radial velocity (Rv)	18.1±0.1[5] km/s
Proper motion (μ)	RA: −1.106 mas/yr[1] Dec.: +6.383 mas/yr[1]
Parallax (π)	3.4219±0.0937 mas[1]
Distance	950 ± 30 ly (292 ± 8 pc)
Absolute magnitude (MV)	−2.22[6]
μ CMa B
Proper motion (μ)	RA: +0.355 mas/yr[3] Dec.: +6.594 mas/yr[3]
Parallax (π)	3.4079±0.0551 mas[3]
Distance	960 ± 20 ly (293 ± 5 pc)
Orbit[7]
Primary	A
Companion	B
Semi-major axis (a)	829 AU
Eccentricity (e)	0.62+0.29 −0.23
Details
μ CMa A
Mass	5.4[1] M☉
Radius	80[1] R☉
Luminosity	1,660[1] L☉
Surface gravity (log g)	1.14[8] cgs
Temperature	4,123[8] K
Rotational velocity (v sin i)	≤ 5[9] km/s
Age	100[8] Myr
μ CMa B
Mass	1.6[10] M☉
Surface gravity (log g)	2.70[10] cgs
Temperature	5,034[10] K
Other designations
μ CMa, 18 Canis Majoris, BD−13°1741, HIP 33345, HR 2593, SAO 152123[11]
μ CMa A: HD 51250[11]
μ CMa B: HD 51251[12]
Database references
SIMBAD	A
	B

Grotius assigned the name Isis to this star, but the name, now obsolete, belonged rather to Gamma Canis Majoris.^[15]

As of 2011, the pair had an angular separation of 2.77 arc seconds along a position angle of 343.9°.^[16] The orange-hued primary member, component A, is an evolved K-type giant star with a stellar classification of K2/3 III^[4] and a visual magnitude of 5.27.^[2] It has 5.4 times the mass, 80 times the radius, and 1,660 times the luminosity of the Sun.^[1] The base magnitude 7.32^[2] companion, component B, is a hybrid B/A-type main-sequence star with a class of B9/A0 V.^[4] It has 1.6 times the mass of the Sun and is the hotter star, having an effective temperature of 5,034 K,^[10] compared to 4,123 K for the primary.^[8]

The system has two visual companions. As of 2008, magnitude 10.32 component C lies at an angular separation of 86.90″, while magnitude 10.64 component D is at a separation of 105.0″.^[17] Mu CMa should not be confused with the 9th magnitude variable star MU CMa located near NGC 2360.^[18]