Nu2 Canis Majoris

Nu² Canis Majoris is a star in the southern constellation of Canis Major. Its name is a Bayer designation that is Latinized from ν² Canis Majoris, and abbreviated Nu² CMa or ν² CMa. With an apparent visual magnitude of 3.96,^[2] it is bright enough to be seen with the naked eye, close to Sirius. An annual parallax shift of around 50.63 mas, as measured by the Gaia spacecraft,^[1] implies a distance of 66.8 light-years (20.5 pc). It is drifting further away with a line of sight velocity of +2.6 km/s.^[4] The star has two confirmed exoplanets^[3] and no known stellar companion.^[8]

For other stars with this Bayer designation, see ν Canis Majoris.

ν² Canis Majoris

Location of ν2 Canis Majoris (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Canis Major
Right ascension	06h 36m 41.038s[1]
Declination	−19° 15′ 21.17″[1]
Apparent magnitude (V)	3.96[2]
Characteristics
Evolutionary stage	Red-giant branch[3]
Spectral type	K1 III[2]
Astrometry
Radial velocity (Rv)	+2.57±0.14[4] km/s
Proper motion (μ)	RA: +62.660 mas/yr[1] Dec.: −69.816 mas/yr[1]
Parallax (π)	48.8490±0.1323 mas[1]
Distance	66.8 ± 0.2 ly (20.47 ± 0.06 pc)
Absolute magnitude (MV)	2.47[2]
Details
Mass	1.439±0.047[5] M☉
Radius	5.198±0.060[5] R☉
Luminosity	13.2±0.7[5] L☉
Surface gravity (log g)	3.165±0.005[5] cgs
Temperature	4,790±27[6] K
Metallicity [Fe/H]	0.21±0.10[6] dex
Rotational velocity (v sin i)	1.97±0.23[4] km/s
Age	4.6±0.7[6] Gyr
Other designations
ν2 CMa, 7 CMa, BD−19°1502, FK5 2510, GC 8624, GJ 239.1, HD 47205, HIP 31592, HR 2429, SAO 151702[7]
Database references
SIMBAD	data

This is an aging giant star with a stellar classification of K1 III,^[2] having exhausted the hydrogen at its core then expanded. It is believed to be on the early ascent of the red giant branch and has not yet undergone helium flash.^[3] This star is around 4.6 billion years old^[6] and is spinning slowly with a projected rotational velocity of 2 km/s.^[4] It has 1.4 times the mass of the Sun and has grown to 5.2 times the Sun's radius. The star is radiating 13 the luminosity of the Sun^[5] from its photosphere at an effective temperature of 4,790 K.^[6]

Planetary system

By measuring periodic variations in the radial velocity of the host star between 2009 and 2010, the Pan-Pacific Planet Search program was able to identify a planet orbiting Nu² Canis Majoris. An orbital fit produced a minimum mass estimate of 2.6±0.6 M_J with an orbital period of 2.1 years and an eccentricity of 0.23. Star spots were ruled out as a source for the signal with a false-alarm probability of 98.7%.^[9] Further observations through 2019 detected the planet, as well as a secondary planet c in a 4:3 orbital resonance with planet b.^[3]

The Nu² Canis Majoris planetary system^[a]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	≥1.940±0.064 MJ	1.800±0.033	736.9	0.055	—	—
c	≥0.912±0.067 MJ	2.205±0.046	988.9	0.046	—	—

Chinese name

In Chinese astronomy, ν² Canis Majoris is called 野雞, Pinyin: Yějī, meaning Wild Cockerel, because this star is marking itself and stand alone in Wild Cockerel asterism, Well mansion (see : Chinese constellation).^[10] 野雞 (Yějī), westernized into Ya Ke. According to R. H. Allen, the name Ya Ke is an asterism consisting ο¹ Canis Majoris and π Canis Majoris, with other small stars in the body of the Dog.^[11]

Notes

1. Masses: Lin et al. (2024)^[5]
   Orbital periods: Luque et al. (2019)^[3]
   Semi-major axes: Lin et al. (2024)^[5]
   Eccentricities: Luque et al. (2019)^[3]