Upsilon Carinae

Not to be confused with Y Carinae.

Upsilon Carinae is a double star in the southern constellation of Carina. Its name is a Bayer designation that is Latinized from υ Carinae, and abbreviated Upsilon Car or υ Car. This pair is part of the Diamond Cross asterism in southern Carina. The Upsilon Carinae system has a combined apparent magnitude of +2.97^[3] and is approximately 1,400 light years (440 parsecs) from Earth.^[2] It is drifting further away with a line of sight velocity of +14 km/s.^[6]

υ Carinae

Location of υ Carinae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Carina[1]
Right ascension	09h 47m 06.12170s[2]
Declination	−65° 04′ 19.2267″[2]
Apparent magnitude (V)	2.97[3] (+3.08/+6.25[4])
Characteristics
Spectral type	A8 Ib + B7 III[5]
U−B color index	+0.13[3]
B−V color index	+0.27[3]
Astrometry
Radial velocity (Rv)	+13.6±0.5[6] km/s
Proper motion (μ)	RA: −11.51[2] mas/yr Dec.: +4.71[2] mas/yr
Parallax (π)	2.27±0.28 mas[2]
Distance	approx. 1,400 ly (approx. 440 pc)
Absolute magnitude (MV)	−5.26[1]
Details
υ Car A
Mass	10.88[7] M☉
Radius	96.6 – 100[7] R☉
Surface gravity (log g)	1.4±0.1[7] cgs
Temperature	7,500±100[7] K
Age	23.4[7] Myr
υ Car B
Mass	8[5] M☉
Surface gravity (log g)	3.3±0.1[5] cgs
Temperature	23,000±1,600[5] K
Other designations
υ Car, CPD−64°1084, GC 13506, HIP 48002, WDS J09471-6504[8]
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.^[9] Consequently, υ Carinae itself is known as 海石五 (Hǎi Dàn wǔ, English: the Fifth Star of Sea Rock.)^[10]

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

Properties

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.^[7] With an apparent magnitude of +3.08,^[4] it has an effective temperature of about 7,500 K,^[7] giving it a white hue. The companion, υ Carinae B, is a giant star with a classification of B7 III,^[4] although Mandrini and Niemela (1986) suggested it may be a subgiant star with a classification of B4–5 IV.^[5] 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.^[5] This system is roughly 12 million years old.^[12]