Omega Carinae

This article is about ω Carinae and is not to be confused with w Carinae.

Omega Carinae, Latinized from ω Carinae, is a star in the constellation Carina. With a declination greater than 70 degrees south of the celestial equator, it is the most southerly of the bright stars of Carina (third-magnitude or brighter), and it is part of a southern asterism known as the Diamond Cross. This star has an apparent visual magnitude of 3.3 and is located at a distance of about 342 light-years (105 parsecs) from Earth.

ω Carinae

Location of ω Carinae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Carina
Right ascension	10h 13m 44.21739s[1]
Declination	−70° 02′ 16.4563″[1]
Apparent magnitude (V)	3.29[2]
Characteristics
Spectral type	B8 IIIe[3]
U−B color index	−0.285[4]
B−V color index	−0.083[4]
Astrometry
Radial velocity (Rv)	+7.0[2] km/s
Proper motion (μ)	RA: -36.01[1] mas/yr Dec.: +7.09[1] mas/yr
Parallax (π)	9.54±0.09 mas[1]
Distance	342 ± 3 ly (104.8 ± 1.0 pc)
Absolute magnitude (MV)	−1.81[5]
Details
Mass	4.9[6] M☉
Radius	7.20±0.14[7] R☉
Luminosity	918[8] L☉
Surface gravity (log g)	3.51[8] cgs
Temperature	11,630[8] K
Rotational velocity (v sin i)	240[8] km/s
Other designations
ω Car, CD−69°1178, FK5 385, HD 89080, HIP 50099, HR 4037, SAO 250885[9]
Database references
SIMBAD	data

Properties

Omega Carinae has a stellar classification of B8 IIIe,^[3] which places it in the category of Be stars, that display emission lines of hydrogen their spectrum. Omega Carinae is a shell star,^[3] having a circumstellar disk of gas surrounding its equator. The luminosity class of III indicates it has evolved into a giant star, having exhausted the hydrogen at its core and left the main sequence. The effective temperature of 11,630 K^[8] in its outer envelope is what gives this star the blue-white hue that is characteristic of B-type stars.

This star is rotating rapidly with a projected rotational velocity of 240 km/s,^[8] which gives a lower limit to the star's azimuthal velocity along the equator. The critical equatorial velocity, at which the star would begin to break up, is 320 km s⁻¹. The star's axis of rotation is inclined by an estimated angle of 70.8° to the line of sight from the Earth.^[10]

In the next 7500 years, the south Celestial pole will pass close to this star (AD 5800) and then I Carinae.^[11]

In culture

In Chinese, 南船 (Nán Chuán), meaning Southern Boat, refers to an asterism consisting of ω Carinae, V337 Carinae, PP Carinae, θ Carinae and β Carinae .^[12] Consequently, ω Carinae itself is known as 南船四 (Nán Chuán sì, English: the Fourth Star of Southern Boat.)^[13]