Omega Canis Majoris

Omega Canis Majoris is a solitary,^[13] blue-white-hued star in the equatorial constellation of Canis Major. Its name is a Bayer designation that is Latinized from ω Canis Majoris, and abbreviated Omega CMa or ω CMa. This star is visible to the naked eye with an apparent visual magnitude of about 4. Based upon an annual parallax shift of 3.56 mas as seen from Earth,^[2] this system is located roughly 920 light-years (280 pc) away from the Sun. It is drifting further away with a line of sight velocity of 23 km/s.^[6]

ω Canis Majoris

Location of ω Canis Majoris (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Canis Major[1]
Right ascension	07h 14m 48.654s[2]
Declination	−26° 46′ 21.60″[2]
Apparent magnitude (V)	3.60 to 4.18[3]
Characteristics
Spectral type	B2.5Ve[4]
U−B color index	−0.73[5]
B−V color index	−0.14[5]
Variable type	γ Cas[3]
Astrometry
Radial velocity (Rv)	23.2±2.4[6] km/s
Proper motion (μ)	RA: −11.617 mas/yr[2] Dec.: +8.109 mas/yr[2]
Parallax (π)	3.5610±0.1524 mas[2]
Distance	920 ± 40 ly (280 ± 10 pc)
Absolute magnitude (MV)	−3.21[1]
Details
Mass	10.1±0.7[7] M☉
Radius	6.2[8] R☉
Luminosity	13,081[9] L☉
Surface gravity (log g)	3.5[10] cgs
Temperature	21,878[10] K
Rotational velocity (v sin i)	80[11] km/s
Age	22.5±2.6[7] Myr
Other designations
ω CMa, 28 Canis Majoris, CD−26°4073, GC 9625, HD 56139, HIP 35037, HR 2749, SAO 173282[12]
Database references
SIMBAD	data

Properties

A visual band light curve for Omega Canis Majoris, adapted from Štefl et al. (2003)^[14]

This star has a stellar classification of B2.5Ve, indicating it is a main sequence Be star, although it has also been classified as a subgiant.^[15] One of the most observed Be stars of the Southern Hemisphere,^[16] Omega Canis Majoris is classified as a Gamma Cassiopeiae-type variable star.^[3] Both the luminosity and the radial velocity vary with a primary cyclical period of 1.372 days.^[17] The variation in brightness, ranging from magnitude +3.60 to +4.18,^[3] shows changes over time, which suggests there are two overlapping periods of 1.37 and 1.49 days. The star also undergoes transient periodicities following outbursts.^[18][11]

This is a massive star with ten^[7] times the mass of the Sun and 6.2^[8] times the Sun's radius. At an estimated age of 22.5 million years,^[7] it is radiating 13,081^[9] times the Sun's luminosity from its photosphere at an effective temperature of 21,878 K.^[10] The star is being viewed nearly pole on, so the measured projected rotational velocity of 80 km/s is only a fraction of the true equatorial velocity, estimated as 350 km/s. It is surrounded by a symmetric circumstellar decretion disk of material that is being heated by the star, which in turn is inserting emission lines into the combined spectrum.^[11]