Upsilon Carinae

Not to be confused with Y Carinae.

Upsilon Carinae, Latinized from υ Carinae, is a double star in the southern constellation of Carina. It is part of the Diamond Cross asterism in southern Carina. The Upsilon Carinae system has a combined apparent magnitude of +2.97^[2] and is approximately 1,400 light years (440 parsecs) from Earth.^[1]

υ Carinae

Location of υ Carinae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Carina
Right ascension	09h 47m 06.12170s[1]
Declination	−65° 04′ 19.2267″[1]
Apparent magnitude (V)	2.97[2] (+3.08/+6.25[3])
Characteristics
Spectral type	A8 Ib + B7 III[4]
U−B color index	+0.13[2]
B−V color index	+0.27[2]
Astrometry
Radial velocity (Rv)	+14[4] km/s
Proper motion (μ)	RA: −11.51[1] mas/yr Dec.: +4.71[1] mas/yr
Parallax (π)	2.27±0.28 mas[1]
Distance	approx. 1,400 ly (approx. 440 pc)
Absolute magnitude (MV)	−5.26[5]
Details
υ Car A
Mass	10.88[6] M☉
Radius	96.6 – 100[6] R☉
Surface gravity (log g)	1.4±0.1[6] cgs
Temperature	7,500±100[6] K
Age	23.4[6] Myr
υ Car B
Mass	8[4] M☉
Surface gravity (log g)	3.3±0.1[4] cgs
Temperature	23,000±1,600[4] K
Other designations
υ Car, CP−64°1084, HIP 48002[7]
A: HD 85124, HR 3890, SAO 250696
B: HD 85123, HR 3891, SAO 250695
Database references
SIMBAD	system
	A
	B

In Chinese, 海石 (Hǎi Dàn), meaning Sea Rock, refers to an asterism consisting of υ Carinae, ε Carinae, ι Carinae, HD 83183 and HD 84810.^[8] Consequently, υ Carinae itself is known as 海石五 (Hǎi Dàn wǔ, English: the Fifth Star of Sea Rock.)^[9]

The primary component, υ Carinae A, has a stellar classification of A8 Ib, making it a supergiant star that has exhausted the hydrogen at its core and evolved away from its brief main sequence lifetime as an B-type star.^[6] With an apparent magnitude of +3.08,^[3] it has an effective temperature of about 7,500 K,^[6] giving it a white hue. The companion, υ Carinae B, is a giant star with a classification of B7 III,^[3] although Mandrini and Niemela (1986) suggested it may be a subgiant star with a classification of B4–5 IV.^[4] The outer envelope of this star has an effective temperature of around 23,000 K, resulting in the blue-white hue of a B-type star.

The two stars have an angular separation of 5.030 arcseconds. As a binary star system, they would have an estimated orbital period of at least 19,500 years and a present-day separation of around 2,000 Astronomical Units.^[4] This system is roughly 12 million years old.^[10]

In the next 7500 years, the south Celestial pole will pass close to these stars and Iota Carinae (8100 CE).^[11]