Nu Ophiuchi (ν Oph, ν Ophiuchi) is a star in the equatorial constellation of Ophiuchus. The apparent visual magnitude is +3.3,^[2] making it one of the brighter members of this constellation. Based upon parallax measurements made during the Hipparcos mission, this star is located about 151 light-years (46 parsecs) from Earth.^[1]

Quick Facts Observation data Epoch J2000 Equinox J2000, Constellation ...

ν Ophiuchi

Location of ν Ophiuchi (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Ophiuchus
Right ascension	17h 59m 01.59191s[1]
Declination	−09° 46′ 25.0798″[1]
Apparent magnitude (V)	+3.332[2]
Characteristics
Spectral type	K0 IIIa CN –1[3]
U−B color index	+0.873[2]
B−V color index	+0.999[2]
Astrometry
Radial velocity (Rv)	12.95 ± 0.41[4] km/s
Proper motion (μ)	RA: –9.48[1] mas/yr Dec.: –116.69[1] mas/yr
Parallax (π)	21.64 ± 0.26 mas[1]
Distance	151 ± 2 ly (46.2 ± 0.6 pc)
Absolute magnitude (MV)	–0.19[5]
Details
Mass	3.04[6] M☉
Radius	14[4] R☉
Luminosity	123[6] L☉
Surface gravity (log g)	2.7[4] cgs
Temperature	4,928[6] K
Metallicity [Fe/H]	0.02[4] dex
Rotational velocity (v sin i)	2.1[4] km/s
Age	330[6] Myr
Other designations
Sinistra, 64 Ophiuchi, BD–09 4632, FK5 673, HD 163917, HIP 88048, HR 6698, SAO 142004, 2MASS J17590160-0946249[7]
Database references
SIMBAD	data

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Nu Ophiuchi has about three times the mass of the Sun and is roughly 330 million years old.^[6] The spectrum of the star matches a stellar classification of K0 IIIa,^[3] indicating it is a giant star that has exhausted the supply of hydrogen at its core and evolved away from the main sequence of stars. Unusually, it displays an anomalously low abundance of cyanogen for a star of its type.^[3] The star's outer envelope has expanded to around 14^[4] times the Sun's radius and now radiates with a luminosity 123^[6] times that of the Sun. This energy is emitted from its outer envelope at an effective temperature of 4,928 K,^[6] giving it the cool, orange hue of a K-type star.^[8]

This is not a binary star system in the sense of having a gravitationally-bound stellar companion.^[9] However, in November 2003, a brown dwarf companion Nu Ophiuchi b was discovered. This sub-stellar companion has at least 21.9 times the mass of Jupiter and takes 536 days (1.47 years) to complete an orbit.^[10] A second brown dwarf companion was discovered in 2010, orbiting further from the star with a period of 3,169 days (8.68 years). These have been confirmed in 2012.^[6] Two brown dwarfs are locked in 1:6 orbital resonance.^[11]

This star is following an orbit through the galaxy that carries it between 23.4–29.2 kly (7.2–9.0 kpc) from the Galactic Center. As a probable member of the Milky Way's thin disk population, it has a low orbital inclination that carries it no more than about 100 ly (31 pc) above the galactic plane.^[12]

This star is sometimes called by the name Sinistra, meaning left side in Latin,^[13] although authors like Jim Kaler recommend not using this name, and instead stick to the Bayer designation only (Nu Ophiuchi).^[14]

In China, the star is part of 天市左垣 (Tiān Shì Zuǒ Yuán), meaning Left Wall of Heavenly Market Enclosure. The stars in this group include ν Ophiuchi, δ Herculis, λ Herculis, μ Herculis, ο Herculis, 112 Herculis, ζ Aquilae, θ¹ Serpentis, η Serpentis, ξ Serpentis and η Ophiuchi.^[15] Consequently, ν Ophiuchi itself is known as 天市左垣九 (Tiān Shì Zuǒ Yuán jiǔ, English: the Ninth Star of Left Wall of Heavenly Market Enclosure), and together with ζ Capricorni represents the state Yan (燕)^[16][17] in the Twelve States constellation.^[18]

• Tau Geminorum