Mu Canis Majoris
Star in the constellation Canis Major
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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.
 | |
| 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 |
| Name | 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]