12 Canis Majoris
Variable star in the constellation Canis Major
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12 Canis Majoris is a variable star located about 707 light years away from the Sun in the southern constellation of Canis Major.[12] It has the variable star designation HK Canis Majoris; 12 Canis Majoris is the Flamsteed designation. This body is just barely visible to the naked eye as a dim, blue-white hued star with a baseline apparent visual magnitude of +6.07.[3] It is moving away from the Earth with a heliocentric radial velocity of +16 km/s.[3] This is the brightest star in the vicinity of the open cluster NGC 2287,[13] although it is probably not a member based on its proper motion.[14]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Canis Major |
| Right ascension | 06h 47m 01.48353s[2] |
| Declination | â21° 00â² 55.4517â³[2] |
| Apparent magnitude (V) | +6.07[3] |
| Characteristics | |
| Spectral type | B7 II/III[4] or B5 V[5] |
| BâV color index | â0.159±0.004[3] |
| Variable type | SX Ari[6] |
| Astrometry | |
| Radial velocity (Rv) | +16.4±2.5[3] km/s |
| Proper motion (μ) | RA: â14.568[2] mas/yr Dec.: +5.778[2] mas/yr |
| Parallax (Ï) | 4.6155±0.0543 mas |
| Distance | 707 ± 8 ly (217 ± 3 pc) |
| Absolute magnitude (MV) | â0.81[3] |
| Details | |
| Mass | 4.8[7] Mâ |
| Radius | 2.73[8] Râ |
| Luminosity | 537[9] Lâ |
| Surface gravity (log g) | 4.23[5] cgs |
| Temperature | 15,830±60[9] K |
| Metallicity [Fe/H] | â0.37[10] dex |
| Rotation | 2.18045 d[7] |
| Rotational velocity (v sin i) | 65[7] km/s |
| Age | 134[11] Myr |
| Other designations | |
| 12 CMa, HK CMa, BDâ20°1576, FK5 817, GC 8884, HD 49333, HIP 32504, HR 2509, SAO 172318[12] | |
| Database references | |
| SIMBAD | data |
The Bayer designation Ï Canis Majoris/Rho Canis Majoris has been applied to this star in the past, but this is now rarely seen.[15] Perhaps the best-known use was by Charles Messier when describing the cluster Messier 41: "cluster of stars below Sirius, near Rho Canis Majoris".[16]
This star has a stellar classification of B7 II/III,[4] matching the spectrum of a B-type star intermediate between a giant and bright giant.[4] (Cidale et al. (2007) show a class of B5 V,[5] which would indicate it is instead a B-type main-sequence star.) It is a magnetic Bp star[17] of the heliumâweak variety (CP4), with the spectrum displaying evidence for vertical stratification of helium in the atmosphere.[18]
Holger Pedersen and Bjarne Thomsen discovered that 12 Canis Majoris is a variable star, in 1977.[19] It was given its variable star designation in 1981.[20] Samus et al. (2017) classify it as an SX Arietis variable that varies in brightness by about 0.05 magnitudes over a period of 2.18045 days.[6] It has 4.8 times the mass of the Sun and 2.73[8] times the Sun's radius. The star is radiating 537 times the Sun's luminosity from its photosphere at an effective temperature of 15,830 K.