Nu2 Canis Majoris
Star in the constellation Canis Major
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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]
 | |
| 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 MJ 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]
| 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]