Nu Geminorum

Nu Geminorum, Latinized from ν Geminorum, is a triple^[5] star system in the constellation Gemini. It has an apparent visual magnitude of 4.16,^[2] which is bright enough to be visible to the naked eye on a dark night. Based upon an annual parallax shift of 5.99 mas,^[1] it is located at a distance of roughly 540 light years from the Sun. The position of this system near the ecliptic means it is subject to lunar occultations.^[9][10]

ν Geminorum

ν Geminorum in optical light
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Gemini
Right ascension	06h 28m 57.78613s[1]
Declination	+20° 12′ 43.6856″[1]
Apparent magnitude (V)	4.16[2]
Characteristics
Spectral type	B6 III + B8 III[3]
U−B color index	−0.47[2]
B−V color index	−0.13[2]
Astrometry
Radial velocity (Rv)	+39.4[4] km/s
Proper motion (μ)	RA: −6.82[1] mas/yr Dec.: −13.10[1] mas/yr
Parallax (π)	5.99±0.28 mas[1]
Distance	540 ± 30 ly (167 ± 8 pc)
Absolute magnitude (MV)	−2.2 + −1.2[3]
Orbit[5]
Primary	ν Gem Aa
Companion	ν Gem Ab
Period (P)	53.7722 ± 0.0008 d
Semi-major axis (a)	2.82 ± 0.02 mas
Eccentricity (e)	0.056 ± 0.003
Inclination (i)	0.98 ± 0.03°
Longitude of the node (Ω)	78.9 ± 0.2°
Periastron epoch (T)	MJD 51011.8 ± 0.1
Argument of periastron (ω) (secondary)	6.7 ± 2.0°
Semi-amplitude (K1) (primary)	51.6 ± 0.6 km/s
Semi-amplitude (K2) (secondary)	52.5 ± 1.1 km/s
Orbit[5]
Primary	ν Gem A
Companion	ν Gem B
Period (P)	6977.3 ± 6.1
Semi-major axis (a)	82.8 ± 1.3 mas
Eccentricity (e)	0.241 ± 0.002
Inclination (i)	75.9 ± 0.2°
Longitude of the node (Ω)	121.0 ± 0.1°
Periastron epoch (T)	MJD 48810.3 ± 13.0
Argument of periastron (ω) (secondary)	226.9 ± 0.4°
Semi-amplitude (K1) (primary)	8.0 ± 0.1 km/s
Semi-amplitude (K2) (secondary)	15.9 ± 0.1 km/s
Details
ν Gem Aa
Mass	3.34[5] M☉
Luminosity	1,380[6] L☉
Temperature	14,100[6] K
Rotational velocity (v sin i)	160[7] km/s
ν Gem Ab
Mass	3.28[5] M☉
ν Gem B
Mass	3.33[5] M☉
Other designations
ν Gem, 18 Geminorum, BD+20°1441, FK5 1173, HD 45542, HIP 30883, HR 2343, SAO 78423, WDS 06290+2013[8]
Database references
SIMBAD	data

The inner components of this multiple star system have an orbital period of about 54 days and a nearly circular orbit with an eccentricity of 0.056.^[5] There is some uncertainty in the spectral type, with classifications ranging from a main sequence star to a giant. Orbiting the inner pair is a classical Be star, with an orbital period of 19.1 years and an eccentricity of 0.24.^[5] The two orbits are co-directional and roughly coplanar. The system is overall dynamically stable, and shows no signs of Kozai-Lidov cycles. The outer Be star appears to be single.^[5]

According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, this star was titled as Nucatai.^[11]

On 15 August 2028, it will be occulted by Venus over Southern Africa and Madagascar.^[12]: 165